30 (2022) 200168
Contents lists available at ScienceDirect
Human Nutrition & Metabolism
journal homepage: www.sciencedirect.com/journal/human-nutrition-and-metabolism
Effect of branched-chain amino acids on food intake and indicators of
hunger and satiety- a narrative summary
Brianna Lueders a, Bradley C. Kanney a, Martina J. Krone a, Nicholas P. Gannon b,
Roger A. Vaughan a, *
a
b
Department of Exercise Science, High Point University, High Point, NC, USA
Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, MN, USA
A R T I C L E I N F O
A B S T R A C T
Keywords:
Ghrelin
Isoleucine
Leptin
Leucine
Peptide-YY (PYY)
Valine
Branched-chain amino acids (BCAA) found in protein are most notably known for their ability to increase protein
synthesis, explaining their appeal to athletes seeking muscle hypertrophy, expedited recovery, and preservation
of lean body mass. In addition to anabolic benefits, protein consumption has been implicated in the regulation of
food intake, which represents an important variable in treating and preventing obesity. Protein-rich foods (such
as dairy) have previously been linked to improved satiety and reduced food intake, however, there appear to be
discrepancies in the effects of different protein types (for example whey versus casein) on appetite. One potential
explanation for these differences is the varied amino acid composition of each protein type. Thus, one theory is
that high levels of BCAA may be responsible in-part for the satiating properties of protein. Therefore, the purpose
of this narrative review is to describe the effects of BCAA (both individually and in combination) on hormonal
regulators of satiety including ghrelin, leptin, peptide tyrosine tyrosine (PYY), cholecystokinin (CCK), and
glucagon-like peptide-1 (GLP-1). This report also summarizes the effect of BCAA on food intake and subjective
measures of hunger. Several reports suggest BCAA stimulate leptin activity (secretion or sensitivity) and GLP-1
levels and suppress ghrelin levels. Similarly, intake is reduced, and subjective measures of hunger are often lower
following consumption of BCAA. However, inconsistencies in experimental protocols and related findings make
the true effect of BCAA on satiety and food intake difficult to discern, and therefor worthy of further
investigation.
1. Introduction
Obesity is a disease classified by body mass index (BMI) > 30 kg/m2
and is potentially associated with increased risk of other obesity-related
comorbidities [1]. Energy intake is of undeniable importance in the
maintenance of healthy body weight, and thus, in the prevention and/or
reduction of obesity. While the regulation of food intake is a complex
process influenced by numerous factors such as meal size, composition,
as well as palatability, manipulation of satiety still represents a poten­
tially viable target in the management of obesity [2]. Interestingly, ev­
idence has shown protein is the most satiating of the macronutrients [2].
Several studies have shown a satiating effect of protein [3], which is
possibly mediated through changes in satiety hormones. It has been
hypothesized that a protein-specific hunger regulation phenomenon,
known as the protein leverage hypothesis, may exist to ensure adequate
protein intake without over-intake [4]. In fact, some studies have
demonstrated a dose-dependent relationship between meal protein
content and post-prandial fullness [5], which may also be influenced by
the method of protein ingestion (beverage or food, whey or casein) [5].
Whey protein has been shown to induce more satiating effects than
casein and other forms of protein, but it is still uncertain as to what
aspects of whey protein produce these stronger satiating effects [6]. One
potential explanation is the differences in amino acid composition be­
tween the two protein types (whey protein contains more
branched-chain amino acids (BCAA)) [6]. BCAA are metabolized by
enzymes branched-chain aminotransferase (BCAT) and branched-chain
alpha-keto acid dehydrogenase (BCKDH), with multiple organs
responsible for their metabolism (however skeletal muscle is the greatest
site) [7]. BCAA are commonly found in a variety of food sources, with
complete proteins such as dairy and meat containing among the greatest
amounts per serving. It has been proposed that proteins (specifically
those with BCAA) could potentially enhance satiety compared to foods
with lower BCAA content. Conversely, others have shown an orexic
* Corresponding author. One University Parkway, High Point, NC, 27268, USA.
E-mail address: rvaughan@highpoint.edu (R.A. Vaughan).
https://doi.org/10.1016/j.hnm.2022.200168
Received 28 August 2021; Received in revised form 17 September 2022; Accepted 27 October 2022
Available online 31 October 2022
2666-1497/© 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
Abbreviations
LCRF
LepR
LHA
MCH
MCR4
MEF2
αMSH
mTOR
NPY
NTS
PMPD
POMC
PPH
PPY
PRO
PVN
PYY
RER
SD
SID
SP
SOCS3
STAT3
VMN
WAT
WP
AgRP
agouti-related peptide
Alpha-MSH alpha-melanocyte-stimulating hormone
AMPK
activated protein kinase
AP
area postrema
ARC
arcuate nucleus
BAT
brown adipose tissue
BCAA
branched-chain amino acid
BMI
body mass index
CART
cocaine- and amphetamine-response transcript
CCK
cholecystokinin
CHO
carbohydrate
CNS
central nervous system
CRH
corticotropin-releasing hormone
DMN
dorsomedial
EAA
essential amino acid
FR
food-restricted
GI
gastrointestinal
GLP-1
glucagon like peptide-1
GLP-1R g-protein coupled GLP-1 receptor
GSHR
growth hormone secretagogue receptor
HFD
high fat diet
IP
intraperitoneal
IR
insulin receptor
KO
SLC6A15 knockout
effect of BCAA due to disrupted ratios of BCAA to other AA, suggesting
BCAA may promote excess energy consumption under certain circum­
stances [8]. Thus, it is unclear what protein components are responsible
for its effects on appetite. Such information may provide foundational
insights on the satiating mechanisms and effects of varied types of
protein and may have benefits for dietary modifications in the preven­
tion of select diseases. Therefore, the primary aims of this review are to
(1) provide a general overview of the regulation of hunger and related
hormones, and (2) summarize the effects of BCAA including leucine,
isoleucine, and valine, as well as mixtures of BCAA on indicators of
satiety including individual hormones, feelings of hunger/satiety, and
food intake (organized first by treatment condition then by experimental
model (cell culture, mouse, rat, etc.) for each outcome). Thus, primary
literature was identified by authors first by searching PubMed using
individual BCAA names and/or “BCAA” with the various satiety hor­
mones or descriptions of outcomes related to satiety (i.e. hunger, full­
ness, buffet intake, etc.). Articles were also identified from reference lists
of primary and review articles identified during the initial search based
on relevance. Articles were summarized if a relevant individual or
combination BCAA treatment and at least one of the commonly used
outcomes as an indicator of satiety were studied, using a representative
model of either basic (cell/tissue culture) or applied (mammalian)
hunger-related physiology. Admittedly, the articles highlighted within
this review are likely not exhaustive given the vast nature of the field
and the broad spectrum of the outcomes that could be measured in
relation to satiety. We also describe the effect of each treatment when
significant differences were reported within the primary manuscript or
estimates when numerical data were not provided within the original
manuscript (expressed as estimated approximation of mean difference
from reference group expressed as a percent increase or decrease from
reference group ± either standard deviation (StDe) or standard error
(SE)). Importantly, estimates of mean differences (denoted by ≈) should
be interpreted as such and readers should consult the cited manuscript
for the first-hand presentation of data.
luminal CCK-releasing factor
leptin receptor
lateral hypothalamic area
melanin-concentrating hormone
melacortin receptor
myocyte enhancer factor 2
alpha-melanocyte-stimulating hormone
mammalian target of rapamycin
neuropeptide Y
nucleus tractus solitarius PBS- phosphate-buffered saline
pre-meal protein drinks
prohormone pro-opiomelanocortin
pea protein hydrolysate
polypeptide Y
protein
paraventricular
peptide tyrosine tyrosine
respiratory exchange ratio
Sprague-Dawley
standardized ileal digestible
soy protein
suppressor of cytokine signaling 3
signal transducer and activator of transcription 3
ventromedial
white adipose tissue
whey protein/whey protein isolate
2. Overview of hormone regulation of hunger
2.1. Ghrelin
Ghrelin is a satiety hormone produced by cells lining the stomach
and pancreas and is released into circulation prior to eating and when
fasting [9]. Ghrelin increases hunger and energy intake, as well as
initiate eating [4], and levels are regulated by food intake and diurnal
eating patterns [9]. Negative energy balance, stimulates an increase in
plasma ghrelin concentrations and increases hypothalamic
AMP-activated protein kinase (AMPK) phosphorylation, thus increasing
food intake [10]. AMPK serves as an intracellular regulator of energy
homeostasis and becomes activated during times of low ATP levels.
Interestingly, ghrelin levels appear to be lower in individuals with
obesity versus lean [11], and the consumption of carbohydrates and
protein decreases circulating ghrelin to a greater extent than fats [12].
One study found Sprague-Dawley (SD) rats perfused with amino acids
via the gastric artery exhibited suppressed ghrelin release versus infu­
sion without amino acids [13].
Mechanistically, after secretion from the stomach, ghrelin travels to
the arcuate nucleus (ARC) in the hypothalamus and binds to the growth
hormone secretagogue receptor (GHSR) in the neuropeptide Y/agoutirelated peptide (NPY/AgRP) neuron [14]. Once bound, NPY neuron
inhibits the anorexigenic pro-opiomelanocortin (POMC) neuron by
releasing the neurotransmitter GABA, which inhibits release of the
α-melanocyte-stimulating hormone (α-MSH) [9]. The activation of the
GHSR also stimulates the activation of AMPK, which promotes tran­
scription of agouti-related peptide, releasing AgRP hormone [10]. AgRP
is antagonistic to α-MSH receptors and blocks MS3/4 receptors in the
hypothalamic nuclei, preventing α-MSH from activating those receptors,
thus inhibiting α-MSH-inhibition of appetite (stimulating hunger) [14].
In addition, the increase in AMPK activity in AgRP neurons drives a
mechanism enhancing mitochondrial fatty acid oxidation and mito­
chondrial biogenesis, enhancing the bioenergetic capacity of AgRP
neurons, and thus ensuring increased cell firing during periods of
negative energy balance (stimulates food intake) [10].
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Human Nutrition & Metabolism 30 (2022) 200168
2.2. Leptin
Intravenous infusion of CCK-8 and CCK-33 (amounts infused were equal
to those typically observed following a mixed-nutrient meal) led to a
20% reduction in energy intake compared with a control [23]. In rats,
exogenously administered CCK had inhibitory effects on energy intake
through the activation of the CCK1 receptor low-affinity sites [24]. When
administered via intraperitoneal administration, another study found
CCK also suppressed energy intake in rats [21]. Moreover, although
mutations in the promoter region for the CCK1 receptor gene are rare,
they have been associated with higher body fat and weight gain [25].
Although exogenous administration of CCK at a single meal may inhibit
energy intake, evidence also suggests that chronic exogenous adminis­
tration may reduce sensitivity to CCK, leading to a weakened anorexic
response [21].
Not surprisingly, interactions between CCK and other gastrointes­
tinal peptides may also enhance or prolong its anorexic effect. Postprandial release of peptide tyrosine tyrosine (PYY) is stimulated as the
small intestine is exposed to nutrients, as well as the signaling from
glucagon-like peptide-1 (GLP-1) and amylin [21]. In rats, the stimula­
tion of PYY release or co-administration of insulin and amylin enhanced
the appetite-suppressing effects of CCK [21]. However, intraperitoneal
administration of CCK-8 and intracerebroventricular leptin caused
greater weight loss in rats than leptin alone, without a change in food
intake, suggesting co-administration of the two promoted weight loss
through means other than energy intake restriction [26]. Thus, further
research on the regulation of appetite is still necessary, however these
findings highlight the importance of considering all regulatory factors in
the regulation of satiety (which is difficult given the experimental
complexities of satiety research).
Peptide tyrosine tyrosine- PYY is a member of the pancreatic poly­
peptide (PP) family, consisting of PP, PYY and NPY [27]. All peptides
within the PP family contain a hair-pin-fold motif structure and bind to
G-protein coupled receptors (GPCR) [27]. PYY is a 36 amino acid pep­
tide produced by L cells and is found in highest concentrations in the
rectum and large intestine [28]. Following energy intake, two forms of
PYY are released into circulation: PYY1-36 and PYY3-36. The predominant
circulating form of PYY in the fasted state is PYY1-36, while
post-prandially, the major circulating form is PYY3-36 [27]. PYY3-36 is
the primary PYY isoform that regulates appetite, and the magnitude of
post-prandial rise in PYY3-36 is proportional to energy consumed.
Moreover, the initial release of PYY3-36 is presumed to be under neural
control, while additional PYY3-36 release occurs as nutrients arrive in the
distal gut [29]. PYY3-36 acts to directly influence appetite through the
Y2-GPCR in the ARC, and indirectly via its action in the ileum (altering
gut motility promoting the feeling of fullness) [27].
Numerous studies in both humans and rodents have shown the
appetite-suppressing effects of PYY3-36. In humans, a 90-min infusion of
PYY3-36 reduced subject food intake by 36% at a buffet meal consumed 2
h after the infusion and reduced 24-h energy intake by 33% compared
with subjects infused with saline [30]. Interestingly, the same group
later examined PYY3-36 and energy intake between subjects with either
obese and lean phenotypes and found no significant difference between
subject types (2-h post-infusion buffet consumption was reduced 30% in
subjects with obesity versus 31% in lean subjects) [31]. A comparable
reduction in energy intake in the subsequent 24 h following infusion
between obese and lean subjects was also observed [31]. Similarly, in
rodents it was found that a single injection of PYY3-36 directly into the
ARC, as well as intra-arcuate administration of a Y2 receptor agonist
caused an inhibition of food intake [30]. In general, PYY3-36 acts to
inhibit appetite through the Y2 receptor in the arcuate nucleus, sup­
pressing the orexigenic NPY neurons while stimulating the activity of
appetite-suppressing POMC/α-MSH neurons [27].
Glucagon-like peptide-1- GLP-1 is produced via the post-translation
proteolysis of proglucagon, a 160-amino acid prohormone. Progluca­
gon is produced in L cells of the distal gut, α-cells of the pancreatic islets,
and within the CNS. GLP-1 is released into circulation in proportion to
energy consumed [32]. Initial release of GLP-1 occurs prior to the food
Leptin is a satiety hormone derived from adipose that suppresses
appetite. During and post-feeding, leptin is secreted into circulation and
binds to systemic receptors (LepR) found in high concentration in the
hypothalamus, particularly in the ARC [14]. Leptin was previously
proposed as an anti-obesity therapeutic agent that may reduce body fat
mass [15]. Although effective at resolving weight gain in those with
genetically inherited leptin deficiency, individuals with diet-induced
obesity often develop leptin resistance [15]. In fact, leptin levels are
positively associated with BMI/fat mass [14], and chronically elevated
leptin levels appear to downregulate LepR, decreasing sensitivity [15].
When leptin is secreted from adipose, it travels to the ARC in the
hypothalamus and binds to LepR on POMC neurons, and the orexigenic
NPY neuron [14]. Once LepR is activated, α-MSH is released from POMC
neurons, and binds to MC3 and MC4 receptors in the paraventricular
(PVN), dorsomedial (DMN), and ventromedial (VMN) hypothalamic
nuclei, as well as in the lateral hypothalamic area (LHA) [14]. The
neuropeptide melanin-concentrating hormone (MCH) regulates appetite
and energy homeostasis, and when the MC3/4 receptors are activated
with α-MSH, MCH is released, suppressing appetite [16]. Activated NPY
neuron LepR also inhibits the release of GABA (a neurotransmitter
responsible for the inhibition of the POMC neurons), further promoting
satiation [16]. In addition to leptin’s direct effect on satiety, it also
indirectly affects hunger stimulation through inhibition/suppression of
AMPK activity in the hypothalamic nuclei which restricts food intake
and stimulates increased energy expenditure [10].
Recent research has focused on the potential clinical utilization of
leptin as a treatment of obesity. Some studies have evaluated the use of
leptin analogs to enhance weight loss in diet-induced obese mice, which
was found to be successful [17]. Conversely, another study demon­
strated that when leptin analogs were administered to humans with
obesity, their body weight and appetite were not significantly affected
[18]. In other cases, researchers have looked at developing agents to
restore leptin sensitivity [19]. In one study, amylin administered
together with leptin was shown to induce weight loss in humans and
rodents, although the potential adverse effects of amylin-leptin admin­
istration warrant further research [15].
2.3. Intestinal regulators of food intake
Cholecystokinin- Cholecystokinin (CCK) is a peptide hormone that is
post-prandially released from the gastrointestinal (GI) tract and func­
tions throughout the central nervous system (CNS) and GI tract. CCK acts
as a neurotransmitter with its highest concentrations found in the ce­
rebral cortex, thalamus, hypothalamus, basal ganglia, and dorsal hind­
brain [20]. CCK is released from I cells of the jejunal and duodenal
mucosa, as well as in vagal afferent neurons, which [18–20] is mediated
by a luminal CCK-releasing factor (LCRF) released from the pancreatic
cells and the duodenal mucosa. CCK slows gastric emptying regulating
GI motility and suppressing energy intake [21]. Various forms of CCK
can be found within the body and are identified by peptide length. Of the
isoforms, CCK-33 and CCK-22 are the most abundant in circulation,
while CCK-8 is the most abundant form in the human brain [21].
Following a meal, macronutrients trigger the release of CCK, thus
increasing plasma concentrations [20].
CCK has 2 types of receptors, CCK1 and CCK2. CCK1 is of greater
importance in terms of appetite regulation, as it has been shown to
reduce energy intake following exogenous CCK administration [21].
While both receptors are located in a variety of tissue, CCK1 receptors
are found in regions of the CNS associated with the regulation of energy
intake, including the nucleus tractus solitarius (NTS), the area postrema
(AP), and the hypothalamic DMN [21]. Several studies have demon­
strated the anorexigenic effects of CCK. In humans, it was found that
exogenous administration of CCK slowed gastric emptying, which could
stimulate the jejunum, while suppressing colonic motility [22].
3
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Human Nutrition & Metabolism 30 (2022) 200168
Fig. 1. Central regulation of hunger and satiety:
Peripheral satiety hormones and gut peptide hor­
mones, such as leptin from adipocytes, neuropeptide
peptide tyrosine tyrosine (PYY) from the intestines
and ghrelin from the stomach, bind and activate their
cognate receptors in the arcuate nucleus (ARC) of the
hypothalamus. Within the ARC, there are anorexi­
genic neurons that express pro-opiomelanocortin
(POMC) and cocaine- and amphetamine-regulated
transcript (CART), as well as orexigenic neurons
that express the neuropeptide Y (NPY) and agoutirelated peptide (AgRP). Various hormones induce
those hunger-regulating effects through activation or
inhibition of those first-order neurons, which in-turn
signal second-order neurons in the hypothalamic
nuclei, including the paraventricular nucleus (PVN),
the dorsomedial nucleus (DMN), the ventromedial
nucleus (VMN), and the lateral hypothalamic area
(LHA). The integration of these signaling mechanisms
contributes to appetite and energy homeostasis.
reaching the distal gut, and is promoted by a meal high in carbohy­
drates, while its second secretion ‘peak’ is stimulated by free fatty acids
in the intestinal lumen following the activation of GPCR [32]. There are
2 forms of GLP-1 that are synthesized, GLP-11-37 and GLP-11-36 amide,
which are cleaved into smaller fragments, GLP-17-37 and GLP-17-36 amide.
GLP-17-36 amide is one of the major circulating bioactive species that
regulates appetite. GLP-1 binds to the GPCR GLP-1 receptor (GLP-1R),
which is expressed in pancreatic islets as well as in various areas of the
CNS, including the ARC and PVN in the hypothalamus and the AP in the
brainstem. When acting on the GLP-1R in pancreatic islets, GLP-1 serves
as an incretin hormone (decreases blood glucose levels), enhancing
glucose-dependent insulin release following energy consumption [27].
GLP-1 also delays gastric emptying and inhibits glucagon secretion,
further contributing to its anorexigenic effect.
Various studies have demonstrated the appetite-suppressing effects
of GLP-1, in both rodents and humans. In rodents, a study demonstrated
that peripheral or central administration of GLP-17-36 amide decreases
food intake, and administration of a GLP-1 antagonist (exendin9-39)
abolishes that anorexigenic effect. In humans, GLP-17-36 amide dosedependently decreased appetite and energy intake in both lean and in­
dividuals that were overweight (lean subjects showed a 13.2% reduction
in energy intake at a buffet meal in comparison to a saline infusion,
while subjects presenting as either overweight or obesity showed a
10.5% reduction in energy intake) [33]. It was also found that admin­
istering injections of GLP-17-36 amide to humans with obesity at meal­
times (4 times per day) over a 5-day period reduced energy intake at
each meal by 15% in comparison to a placebo [34]. Other studies have
further demonstrated that GLP-1R agonists, such as Exenatide, and
long-acting analogs such as liraglutide, decrease food intake, promoting
weight loss through the reduction of gastric emptying and central effects
of the CNS [35].
The action of PYY3-36 and GLP-17-36 amide together remains a topic of
current investigation, however the two gut hormones may act syner­
gistically to enhance anorexigenic effects. In a study involving lean
humans, intravenous infusion with both PYY3-36 and GLP-17-36 amide led
to a reduction in food intake by 27% during a buffet meal that was
served 90 min into the infusion (infusion continued during the meal)
[36]. However, single infusions of either hormone failed to decrease
energy intake compared with saline infusions. In rodents, the peripheral
co-administration of PYY3-36 and GLP-17-36 amide showed a reduction in
food intake greater than either hormone individually, and at twice the
dosage [36]. Although further research is still needed for the use of
exogenous hormones and their anorexigenic effects (both individually
and concomitantly), which may represent new methods of ‘treating’
obesity. Fig. 1 summarizes many of the aforementioned mechanisms of
satiety regulation.
3. Effect of BCAA on indicators of satiety and food intake
3.1. Effect of BCAA on ghrelin
We initiated our summary on the effect of BCAA on the various
4
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Human Nutrition & Metabolism 30 (2022) 200168
Table 1
Summary of the effect of BCAA on ghrelin. Abbreviations: AA, amino acid mixture; CPE, cocoa polyphenolic extract; EAA, essential amino acids; F, female; FR, food
restriction; HFD, high-fat diet; HP, high protein; IDI, intraduodenal infusion; I, isoleucine; L, leucine; M, male; ND, no difference; OB, obese; PPH, pea protein hy­
drolysate; SD, Sprague-Dawley; StDe, standard deviation; SE, standard estimate of the mean; SP, soy protein; SPF, specific pathogen-free; SPI, soy protein isolate; WP,
Whey protein/Whey protein isolate; WT, weight; V, valine; V:LYS, valine:lysine ratio. Notes: effects noted within “Ghrelin” column are reported as raw values (if
available) or as estimates (indicated by ≈) of percent change from control mean ±the variability for the treated group. “?” next to StDe indicates the type of variability
presented was unclear.
Treatment
Experimental Model
Dosing Notes
Comparison
Ghrelin
Reference
AA
SD rats, (n = 12)
isolated stomachs
Healthy M (n = 12)
Healthy M (n = 11)
AA- infusion (5X), 15 min
Base media (control)
[13]
L- IDI, 0.15 or 0.45 kcal/min (3.3/9.9 g)
L- 90-min IDI 3.3 g or 9.9 g
Saline (control)
Isotonic control solution (glycine)
V-standardized ileal digestible V:Lys 0.65
V- standardized ileal digestible V:Lys
0.45
V- standardized ileal digestible V:Lys
0.46
↔ mRNA (ND)
[39]
AA
Healthy piglets/gastric
tissue (n = 12)
Healthy piglets/
duodenal tissue (n =
12)
Older F (n = 10)
↓ secretion (-≈30% ±≈20%
(StDe?)
↔ plasma (ND)
↓ plasma (− 38 (AUC) ±1282
(StDe)
↔ mRNA (ND)
[40]
AA
Older F (n = 10)
AA
L
L
V
V
WP
WP
WP
WP
WP
WP
V- standardized ileal digestible V:Lys 0.66
[37]
[38]
[39]
AA Mixture- Oral, (bar)(565 kJ); EAA (7.5 g, 40%
L-L)
AA Mixture- (gel)(477 kJ); EAA (7.5 g, 40% L-L)
Control (nothing)
Adolescence w/obesity
(n = 14)
SPF Wistar rats M (n =
12)
AA Mixture- 306 kJ in orange juice
Maltodextrin 306 kJ in orange juice
↓ plasma (trend) (− 33 pg/ml
(±83 pg/ml (StDe))
↓ plasma (trend) (− 35 pg/ml
(±104 pg/ml (StDe))
↔plasma (ND)
WP- (1.1 kcal/g; 35% whey, 35% sucrose, 30%
corn oil)
WP- Oral (beverage)
↓ plasma (− 4 ng/ml (±0.2
ng/ml (StDe)), ↔ plasma
(AUC) (ND)
↔ plasma (ND)
[42]
Healthy subjects (n =
14)
Healthy subjects (n =
25)
Healthy subjects (n =
25)
Subjects w/overweight
or obesity (n = 73)
Subjects w/overweight
(n = 39)
NUTRALYS pea protein (1.1 kcal/g;
35% pea protein, 35% sucrose, 30%
corn oil)
SPI- Oral, pre-meal (beverage/water)
WP- Breakfast custard of WP w/normal protein
(pro/carb/fat = 10/55/35 En%)
WP- Breakfast custard of WP w/high protein (25/
55/20 En%)
WP- Oral (beverage), 52 g/packet, 1670 kJ/d:
Breakfast custard of soy or casein
protein
Breakfast custard of soy or casein
protein
SP- 52 g/packet, 1670 kJ/d:
↔ plasma (ND)
[44]
↔ plasma (ND)
[44]
[45]
WP- Oral (beverage/shake), 300 mL, 1024 kJ, %
energy from pro/carbs/fat = 25/42/33 w/150 mL
water: WP (15 g WP)
PPH (300 mL, 1024 kJ, 15 g PPH)
↓ plasma (− 85 ng/ml (±36
ng/ml (StDe))
↔ plasma (ND)
satiety hormones beginning with ghrelin, an orexigenic hormone.
Infusion of media supplemented with amino acids into SD rats reduced
ghrelin release (by ~30%) when compared to basal media [13]. Inter­
estingly, ghrelin concentrations in response to BCAA have been either
unaltered or decreased, demonstrated across several studies with vary­
ing subjects. For example, on three separate occasions, leucine was
intraduodenally infused to 12 healthy-weight males for 90 min, at either
0.15 kcal/min, 0.45 kcal/min or saline control. Blood samples were
taken at 10 min prior to consumption, at baseline, and every 15 min
during the infusion. Leucine administration had no effect on plasma
ghrelin levels in comparison to the control saline solution [37]. Steinert
et al. retrospectively analyzed the effect of individual amino acids
(including leucine) from four previous trials on ghrelin following 90-min
intraduodenal amino acid infusions and observed reduced ghrelin levels
following leucine infusion versus glycine [38]. Although relatively
underexplored, valine has also been examined for its effect on ghrelin.
For example, piglets given varied levels of valine (indicated by the
standardized ileal digestible (SID) valine to lysine ratio) were assessed
for ghrelin mRNA expression in both gastric and duodenal tissue, both of
which were unaltered by valine content [39].
Mixtures of amino acids have also been investigated for their effects
on ghrelin. One study consisting of older females (68.4 ± 4.5 years)
given either a bar (565 kJ) or gel (477 kJ), both rich in essential amino
acids (EAA) (7.5 g, 40% L-leucine), demonstrated a decrease in the
amount of acylated ghrelin levels over 1 h compared to the control
(consumed nothing) [40]. This study may indicate higher levels of EAA
could potentially result in a reduction in activated ghrelin levels [40].
Conversely, findings have from a trial examining the effects of a mixture
of EAA including leucine showed adolescents with obesity had a similar
ghrelin response following amino acid supplementation as the control
group [41]. Interestingly, in a study assessing changes in plasma ghrelin
Control (nothing)
[40]
[41]
[43]
[46]
following the consumption of whey or pea protein in 10 male SPF Wistar
rats, the rats received either a non-protein (70% sucrose, 30% corn oil),
whey protein (35% whey, 35% sucrose, 30% corn oil), or pea-protein
(35% pea-protein, 35% sucrose, 30% corn oil) test meal, with blood
samples collected at 20, 40, 60, 120, and 180 min following consump­
tion. Whey protein resulted in significantly lower plasma ghrelin when
compared to pea protein [42], and at 40 and 60 min following con­
sumption, whey protein decreased ghrelin levels to a greater extent than
pea protein and carbohydrates [42]. However, a study performed with
14 healthy-weight subjects (5 M/9 F, age: 20–28 years) given either
water or one of six different pre-meal protein drinks (PMPD) immedi­
ately prior to a standard reference meal, found no significant difference
in the plasma ghrelin levels or appetite between the PMPD meals and the
control [43]. Similar findings were also demonstrated using 25
healthy-weight subjects (11 M/14 F, age: 22 ± 1 years) that completed 6
different trials, each a week apart [44]. Subjects were given a stan­
dardized custard breakfast containing either whey, casein, or soy as the
single source of protein, and either normal protein (pro/carb/fat =
10/55/35% energy) or high protein (25/55/20% energy) content [44].
Blood hormone and subjective hunger ratings were collected prior to,
and for several hours following breakfast consumption, followed by an
ad libitum lunch [44]. No differences in ghrelin concentrations were
observed between any of the treatments, however energy intake in the
whey protein group was consistently lower compared to the soy and
casein groups (albeit not significantly), in both the normal and high
protein content breakfasts [44].
Although findings are mixed, there is evidence supporting the
decrease in ghrelin concentrations that occurs following BCAA con­
sumption. In a 23-week study using 73 subjects with either overweight
or obesity (34 M/39 F, age: 40–62 years), a beverage packet of 52 g
(1670 kJ/d) containing one of three treatments (whey protein (WP)
5
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
administered either leptin or vehicle control (phosphate-buffered saline
(PBS)) for the remaining 6 weeks, and food intake was assessed [52].
While administration of leptin alone had no significant effect on food
intake in the chow-water group, the Chow-Leu group exhibited signifi­
cantly decreased food intake. This finding suggests chronic leucine
administration can increase leptin sensitivity [52]. Furthermore, male
C57BL/6J mice fed either a regular rodent chow (20% protein energy)
or a HFD (20% protein energy, 60% fat energy) ad libitum, were given
water either with or without leucine (1.5% wt/vol) [53]. Blood samples
were analyzed after 14 weeks and plasma leptin levels were decreased in
the HFD-Leu group compared with the HFD-Water group (although the
effect was lost after controlling for adiposity as leucine-treated mice
experienced significantly less weight gain versus HFD-Water), perhaps
suggestive of increased leptin sensitivity [53]. Energy intake for the
Chow-Leu group increased 8.4% compared to the Chow-W group,
whereas no significant difference in caloric intake was seen between the
HFD-leu and HFD-W groups [53].
Similarly, leucine has been shown to alter leptin signaling in rats. For
example, meal-trained SD rats gavaged with leucine (2.5 ml/100 g of
bodyweight of 5.4% leucine in water) displayed significantly elevated
circulating plasma leptin levels 3 h post-ingestion versus the saline
control [54]. The study also demonstrated that the removal of either
leucine or BCAA from the diet reduced post-prandial leptin response to
feeding [54]. Additionally, this study investigated the influence of
mTOR on plasma leptin secretion using rapamycin-treated rats via
intraperitoneal injection, and showed rapamycin reduced plasma leptin
concentrations [54]. These findings support a role of mTOR in leptin
production [54], and are similar to other findings demonstrating leucine
induces leptin secretion in an mTOR-dependent fashion [49].
Conversely, a report by Yuan et al. using male SD rats divided into four
groups (HFD, HFD +1.5% Leu, HFD +3.0% Leu, or HFD +4.5% Leu)
with food dispensed daily, showed suppressed serum leptin levels in the
leucine-supplemented groups [55]. Specifically, serum leptin levels
were significantly lower in the three leucine groups when compared to
HFD only, while no significant difference in leptin levels was observed
between the three leucine groups [55]. Importantly, however, each of
the leucine-supplemented groups also displayed significantly greater
hypothalamic and adipose LepR content versus HFD-only, again sug­
gesting improved leptin sensitivity [55]. Additionally, no significant
difference in food or energy intake was observed between the four
groups [55]. In another study using 30 male SD rats with obesity given a
chronic HFD for 15 weeks, rats received one of four treatments (control
diet, control diet +5% leucine, control diet with endurance training, and
control diet with endurance training and leucine) [56]. Food intake and
body weight of rats within each treatment group were recorded daily for
6 weeks, after which serum leptin was measured [56]. No significant
difference in energy intake or serum leptin concentrations was observed
among the four groups, and serum leptin levels appeared to be unaf­
fected by leucine supplementation [56].
Similar studies have been conducted using Wistar rats. For example,
older Wistar rats (18-months-old) were given ad libitum access to a
control diet (fortified with lysine as control) or leucine diet (4.5%) for 6
months [57]. After 6 months, rats received either a bolus of water
(post-absorption state; PA), or a bolus including 1 g glucose, 1.2 g su­
crose and 1 g AA mixture (post-prandial state; PP) [57]. Rats were then
sacrificed, and blood was collected [57]. Leptin levels in adipose tissue
were quantified using an ELISA, and it was found that leptin levels
within the white adipose tissue of the leucine group was significantly
higher than that of the control group (as were plasma leptin levels) [57].
In another study, male Wistar rats received 50% food-restriction (FR) via
AIN-93 M diet (14% egg albumin pro) for 3 weeks and were then
randomly assigned to receive a control or leucine (~0.6% leucine) diet
[58]. Although not statistically significant, serum leptin levels were
lower in the leucine group versus the control group (− 47%), however
LepR expression was not assessed [58].
In addition to individual BCAA, a by Solon-Biet et al. investigated the
concentrate-80, isoflavone-free soy protein isolate (SP), and maltodex­
trin (CHO)), was consumed either immediately prior to, during, or
immediately after breakfast and dinner twice per day. Plasma samples
were taken following a 12-h fast at baseline and after 12, 16, 20 and 23
weeks. Plasma ghrelin concentrations were significantly lower in the WP
group compared to both SP and CHO groups [45]. Conversely, in the
first part of a two-part, randomized, single-blind crossover study con­
sisting of 39 subjects considered overweight (19 M/20 F, 18-60
years-old), subjects consumed one of four shakes (pro/carb/fat =
25/42/33%, 1024 kJ) in a randomized order including WP (15 g WP),
pea protein hydrolysate (PPH) (15 g PPH), WP + PPH (7.5 g WP, 7.5 g
PPH), or mixed protein (MP) (15 g MP, 80% casein and 20% WP). Blood
samples were collected at 30, 60, 90, and 120 min after consumption
while an appetite questionnaire was completed at 30, 60, 90, 120, 180,
and 240 min post-consumption. Ghrelin levels and other biological in­
dicators of satiety/hunger did not differ significantly between the WP or
PPH [46]. Thus, although the effect of BCAA on ghrelin levels (and
activation) is unclear, some evidence suggests BCAA may exert a sati­
ating effect in-part by depressing ghrelin signaling with 4 out of 9 studies
identified showing significantly reduced circulating ghrelin concentra­
tions and the remaining 5 reporting no effect (Table 1). Importantly, 3
studies demonstrating a significant reduction in ghrelin used WP treat­
ments suggesting combinations of amino acids rather than individual
BCAA (namely leucine) may be required to alter ghrelin secretion.
3.2. Effect of BCAA on leptin secretion and sensitivity
BCAA have also been linked with modified leptin production,
secretion, and sensitivity. For example, in vitro experiments performed
using 3T3-L1 adipocytes treated with leucine from 1 to 15 mM for 48 h
showed a significant increase in leptin secretion by 26–37% [47].
Similarly, white adipocytes isolated from epididymal fat pads of male
Wistar rats were incubated for 4 h with either leucine or valine (both at
5 mM concentrations), in either the presence or absence of glucose
and/or the presence or absence of insulin showed significantly increased
leptin in the leucine groups with glucose when compared to the control
(an effect not observed without glucose) [48]. Interestingly, when
incubated with valine, significantly increased leptin levels were
observed both with and without glucose or insulin when compared to
the control [48]. Additionally, using mTOR-inhibitory experiments with
rapamycin, leucine’s effects were shown to be mTOR-dependent in
primary adipocytes from SD rats given leucine at 5 mM for up to 4 h,
suggesting leucine activates the mTOR pathway, which in-turn increases
protein synthesis and leptin production at the post-transcriptional level
[49]. Moreover, myotubes supplemented with leucine at 5 mM exhibited
significantly elevated LepR mRNA abundance versus the control, indi­
cating that leucine may increase leptin sensitivity [50]. In the same
report, 5 mM leucine for various durations significantly increased LepR
protein expression at 1 h and reached its peak at 2 h [50].
In vivo, leucine has also been shown to alter leptin signaling and
sensitivity. For example, male C57BL/6 mice were individually housed
with food and water ad libitum during a 3-day acclimation period [51].
Following acclimation, mice were fed a non-purified rodent diet (13.42
MJ/kg) with either 3% (wt/wt) leucine or 2.04% (wt/wt) alanine
(control) [51]. After 14 days, plasma leptin concentrations were quan­
tified, and the gastrocnemius and soleus muscles were assessed for
changes in LepR mRNA and protein expression [51]. Leucine supple­
mentation increased plasma leptin concentration in the C57BL/6 mice
by 20%, as well as induced mRNA and protein expression of the LepR in
the gastrocnemius and soleus muscles [51]. Conversely, six-week old
male C57BL/6J mice were individually housed and given a high fat diet
(HFD) (pro/carb/fat = 20/20/60%) for 8-weeks following a 1-week
acclimation period [52]. Mice were then given standard chow pellets
(30/20/50%) and evenly distributed into two groups (water with or
without 1.5% leucine (wt/vol)) for 21 weeks [52]. After 15 weeks, leptin
levels remained unchanged [52]. Interestingly, mice were then
6
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
Table 2
Summary of the effect of BCAA on leptin. Abbreviations: AA, amino acid mixture; CAS, Casein; CPE, cocoa polyphenolic extract; HFD, high-fat diet; HP, high protein;
L, leucine; M, male; ND, no difference; SD, Sprague-Dawley; StDe, standard deviation; SE, standard estimate of the mean; SP, soy protein; SPI, soy protein isolate; WP,
whey protein/Whey protein isolate; WT, weight; V, valine. Notes: effects noted within “Leptin” column are reported as raw values (if available) or as estimates
(indicated by ≈) of percent change from control mean ±the variability for the treated group. “?” next to StDe indicates the type of variability presented was unclear.
Treatment
Experimental Model
Dosing Notes
Comparison
Leptin
Reference
L
3T3-L1 adipocytes
L- 1–15 mM (48 h)
Wistar rats M − isolated
adipocytes
Wistar rats M − isolated
adipocytes
C2C12 myotubes (n = 6)
L- with glucose
L- with glucose and insulin
No AA
↑ secretion (media) (27–36% or ≈100 pg/
ml)
↑ secretion (media) (≈100% ± <20%
(SE)), ↔ without insulin (ND)
↑ secretion (media) (≈20% ± <20% (SE))
[47]
L
0.5 ug/mL of CPE and 1–15
mM L, or just CPE
No AA
L- 5 mM supplemented starvation
media (0–6 h)
No L media
[50]
C57BL/6J mice M (n = 20)
and ob/ob mice M (n = 24)
C57BL/6J mice M (n = 6)
gastrocnemius
L- 3% (wt/wt) supplemented diet
(13.42 MJ/kg)
L- 3% (wt/wt) supplemented diet
(13.42 MJ/kg)
Rodent diet with 2.04% Lalanine
Rodent diet with 2.04% Lalanine
↑ sensitivity/leptin receptor mRNA
(≈200% ± ≈60% (SE)) and ↑protein
(≈100% ± ≈10% (SE))
↑ plasma (≈20% ± <10%(SE))
[51]
L
C57BL/6J mice M (n = 6)
soleus
L- 3% (wt/wt) supplemented diet
(13.42 MJ/kg)
Rodent diet with 2.04% Lalanine
L
L
C57BL/6J mice (n = 9–11)
C57BL/6J mice M (n = 5)
Water (control)
Chow
L
C57BL/6J mice M (n = 5)
HFD
↓ plasma (− 18.1 ng/ml ±5.4 (SE))
[53]
L
C57BL/6J mice M, HFD (n
= 37–39)
SD rats M − adipocytes from
epididymal fat pads
L- 1.5% (wt/vol) supplemented H2O
L- 1.5% (wt/vol) supplemented H2O,
regular rodent chow (20% pro cal)
L- 1.5% (wt/vol) supplemented H2O,
HFD (20% pro cal 60% fat)
L- (6% wt/wt fat)
↑ (sensitivity/leptin receptor) (≈150%
fold ± ≈20% (SE)) and ↑protein (≈100%
± ≈10% (SE))
↑ (sensitivity/leptin receptor) (≈200% ±
≈20% (SE)) and protein (≈100% ± ≈10%
(SE))
↔ secretion (ND)
↔ plasma (ND)
HFD (10% wt/wt WP content)
↔mRNA (ND)
[61]
L- 5 mM (0–4 h)
No L
[49]
L- Oral (gavage-fed), 54 g/L, 2.5 mL/
100 g
L- 1.5–4.5% L supplementation C11
Saline (control)
↑ secretion (media) at 4 h (≈200–300% ±
<20% (SE)) (varied experiments), ↔
mRNA (ND)
↑ plasma (≈1 ng/ml (±0.5 (SE))
[55]
L- 5% supplementation to diet
Control diet
↓ serum (20–30% ± ≈10% (SD)), ↑ leptin
receptor (20–50% ± ≈10–20% (SD)),
↔ serum (ND)
L- 50% FR AIN-93 M diet with ~0.6% L
supplementation (1.773% L)
L- 4.5% added to diet
50% FR AIN-93 M diet (1.182%
L)
Control diet
↔ serum (ND)
[58]
[57]
L or BCAA- (AIN-93 M, pro/carb/fat =
20/20/60%) or normal diet (20/63/
17%)
V- with and without glucose and
insulin
V- with and without glucose and
insulin
BCAA- Varied (50%)
CAS (control)
↑ plasma (16.5 ng/ml ±3.9 (SE)) and
adipose tissue (13 ng/ug ±0.06 (SE))
↔ plasma in BCAA or L vs control for
normal or HFD (ND)
↑ secretion (media) both with and without
insulin
↑ secretion (media) both with and without
insulin
↑ plasma (≈200% ± <10% (SE))
[48]
↑ plasma (≈200% ± <10% (SE))
[8]
↑ plasma (≈400% ± <10% (SE))
[8]
↓ serum (≈3.98 ng/ml ±4.8 ng.ml) and
↔mRNA (ND)
↓ serum (2.82 ng/ml ±4.8 ng.ml) and
↓mRNA (≈50% ± <20% (SE))
↓ serum (3–4 ng/ml ±4.8 ng.ml) and
↓mRNA (≈30% ± <20% (SE))
↓ mRNA (53% ± 5% (SE))
[59]
Control (HFD pro/carb/fat =
16/44/40%), soy, milk and redmeat pro
Control (low protein (14%))
↔ serum (ND)
[62]
↔ plasma (ND)
[60]
Collagen 38 g
Flavored water (<1 kcal)
↔ plasma (ND)
↔ plasma (ND)
[65]
[64]
L
L
L
L
L
L
SD rats M, (n = 12)
L
SD rats M, HFD (n = 12)
L
L
SD rats M, HFD w/obesity
(n = 7–8)
Wistar rats M (n = 28)
L
Wistar rats (n = 89)
L
SD rats overweight M, HFD
(n = 8)
V
BCAA
Wistar rats M − isolated
adipocytes
Wistar rats M − isolated
adipocytes
C57BL/6J mice (n = 16–18)
BCAA
C57BL/6J mice (n = 16–18)
BCAA
C57BL/6J mice (n = 16–18)
BCAA
Finishing pigs (n = 8)
BCAA
Finishing pigs (n = 8)
BCAA
Finishing pigs (n = 8)
WP
C57BL/6J mice M, HFD (n
= 37–39)
C57BI/6J mice M (n =
9–10)
V
WP
WP
SD rats M (n = 30)
WP
WP
F w/obesity (n = 37)
M w/diabetes (n = 11)
BCAA- Varied (200%, 100%, 50%, and
20%)
BCAA- Varied (200%, 100%, 50%, and
20%)
BCAA- 2:1:1 (L:I:V) with low-protein
diet for 43 days
BCAA- 2:2:1 (L:I:V) with low-protein
diet for 43 days
BCAA- 2:1:2 (L:I:V) with low-protein
diet for 43 days
WP- (20% wt/wt fat) and 50% wt/wt
WP content
HP- chow (pro/carb/fat = 30/30/
40%) of WP~15%
HP- 24% (wt/wt) of WP (HP-W) or
isoflavone-free SP (HP-S)
WP – 40 g
WP/WPH- 15 g (68 kcal)
HFD
No AA
No AA
Normal diet with 20% normal
BCAA
Normal diet with 20% normal
BCAA
Normal diet with 20% normal
BCAA
Low-protein diet
Low-protein diet
Low-protein diet
HFD (10% wt/wt WP content)
effect of varied BCAA content on food intake and leptin levels in C57BL/
6J mice [8]. Mice were given either a reference diet (100% BCAA con­
tent), twice (200%) the BCAA content of the reference diet, 50% the
BCAA content of the reference diet, or 20% the BCAA content of the
[48]
[48]
[51]
[51]
[52]
[53]
[54]
[56]
[63]
[48]
[8]
[59]
[59]
[61]
reference diet [8]. Monthly energy intake was significantly higher in the
200% BCAA group versus all other groups, while leptin levels were
lower in the 20% group versus all other groups, and 50% was lower than
200%, suggesting BCAA increased leptin concentrations [8]. However,
7
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
Table 3
Summary of the effect of BCAA on gut-secreted hormones. Abbreviations: AA, amino acid mixture; EAA, essential amino acids; F, female; HFD, high-fat diet; HP,
high protein; ID, intraduodenal infusion; I, isoleucine; L, leucine; M, male; ND, no difference; PPH, pea protein hydrolysate; SD, Sprague-Dawley; StDe, standard
deviation; SE, standard estimate of the mean; SP, soy protein; SPF, specific pathogen-free; WP, Whey protein/Whey protein isolate; WT, weight; V, valine; V:LYS,
valine:lysine ratio. Notes: effects noted within “Response” column for each hormone are reported as raw values (if available) or as estimates (indicated by ≈) of percent
change from control mean ±the variability for the treated group. “?” next to StDe indicates the type of variability presented was unclear.
Treatment
Experimental Model
Dosing
Comparison
Response (CCK)
Reference
L
Proximal porcine jejunal
tissue
L- 2.5, 5, 10, 20 mM for 1–3 h or 10 mM for 2 h
Alanine (isonitrogenous control)
[66]
L
Healthy M (n = 12)
L - IDI, 0.15 kcal/min
Saline
L
Healthy M (n = 12)
L - IDI, 0.45 kcal/min
Saline
L
L - gastric infusion, 1.56 g L
Tap water
L
Healthy subjects and
subjects w/overweight (n
= 20)
Healthy M (n = 12)
↑mRNA and protein
secretion (varied time and
dose effects)
↑ plasma (<1 pMol/L ±
≈0.1 (SE))
↑ plasma (≈1 pMol/L ±0.5
(SE))
↔ plasma (ND)
L - gastric infusion, 5 g or 10 g L
Suspension Control
[68]
L
Healthy M (n = 9–11)
L - 90-min IDI 3.3 g or 9.9 g L
I tonic Control solution (glycine)
L
Healthy M (n = 16)
Isotonic saline
I
Proximal porcine jejunal
tissue
L – intraduodenal infusion, 0.45 kcal/min (41
kcal)
I- 2.5, 5, 10, 20 mM for 1–3 h or 10 mM for 2 h
V
Healthy piglets/gastric
tissue (n = 12)
Healthy piglets/duodenal
tissue (n = 12)
Healthy M (n = 12)
Proximal porcine jejunal
tissue
Proximal porcine jejunal
tissue
V- standardized ileal digestible V: Lys 0.65
V standardized ileal digestible V: Lys
0.45
V standardized ileal digestible V: Lys
0.46
Saline Control
Alanine (isonitrogenous control)
↑plasma versus baseline
(5g only) (effect magnitude
unclear)
↑ plasma (82 (AUC) ±9
(SD)
↑ plasma (effect magnitude
unclear)
↑mRNA and protein
secretion (varied time and
dose effects)
↓ mRNA (≈45% ± <20%
(SE))
↔ mRNA (ND)
[70]
[66]
L:I:V (1:0.51:0.63)- 2.5, 5, 10, 20 mM for 1–3 h or
10 mM for 2 h
Alanine (isonitrogenous control)
WP
SPF Wistar rats M (n = 12)
WP- (1.1 kcal/g; 35% WP, 35% sucrose, 30% corn
oil)
WP
WP
SD rats M (n = 30)
Subjects w/overweight (n
= 39)
↔ plasma (ND)
↑ plasma (11.6 pMol ±69.3
pMol)
[60]
[46]
WP
Healthy M (n = 20)
WP- High protein 24% (wt/wt) of WP
WP- Oral (beverage/shake), 300 mL, 1024 kJ, %
energy from pro/carbs/fat = 25/42/33 w/150
mL water: WP (15 g WP)
Protein- 3 kcal/min, ID infusion, 90-min
NUTRALYS pea protein (1.1 kcal/g;
35% pea protein, 35% sucrose, 30%
corn oil)
Low protein Control (14%)
PPH (300 mL, 1024 kJ, 15 g PPH)
↔ plasma (ND)
↔mRNA and protein
secretion (ND)
↑mRNA and protein
secretion (varied time and
dose effects)
↔ plasma (ND)
[71]
WP
Healthy M (n = 12)
WP- 3 kcal/min ID infusion, 60-min
Saline Control
WP
Healthy M w/obesity (n =
12)
Healthy M w/obesity (n =
12)
Healthy subjects (n = 5)
WP- 1.5 kcal/min ID infusion, 60-min
Saline Control
WP- 3 kcal/min ID infusion, 60-min
Saline Control
WP- Oral, load of WP (8 g) plus glucomannan (1
g) (0–3 h)
Oral, load of CAS (8 g) plus
glucomannan (1 g)
↑ plasma (164 (AUC) ±38
(SE)
↑ plasma (130 (AUC) ±33
(SE)
↑ plasma (47 (AUC) ±12
(SE)
↑ plasma (83 (AUC) ±16
(SE)
↔ plasma (ND)
V
V
V
BCAA
WP
WP
V- standardized ileal digestible V: Lys 0.66
V- 90-min IDI 3.3 g or 9.9 g L
V- 2.5, 5, 10, 20 mM for 1–3 h or 10 mM for 2 h
Alanine (isonitrogenous control)
Saline Control
[37]
[37]
[67]
[38]
[69]
[66]
[39]
[39]
[66]
[42]
[72]
[72]
[72]
[73]
Treatment
Experimental Model
Dosing
Comparison
Response (GLP-1)
Reference
L
STC-1 cells
L- 37.5 mM - 150 mM for 12–36 h
Control
[74]
L
L
NCI-H716 cells
C57BL/6J mice M (chow)
L- approximately 114 mM-150 mM for 18 h
L- gastric infusion, 3.5 mmol/kg L for 6 days
Control
Saline
L
C57BL/6J mice M (high-fat
diet)
SD rats M (n = 4)
Healthy M (n = 12)
Healthy M (n = 12)
Healthy M (n = 12)
L- intragastric L (3.5 mmol/kg for 6 days) HFD
Saline + HFD
L- 50 mM intestinal infusions
L- ID infusion, 0.15 kcal/min
L- ID infusion, 0.45 kcal/min
L- gastric infusion, 5 g or 10 g L
Baseline
Saline
Saline
Suspension Control
Healthy subject and subjects
w/obesity (n = 20)
Healthy M (n = 11)
Healthy subjects (n = 12)
Healthy subjects (n = 12)
Healthy M (n = 12)
NCI-H716 cells
SD rats M (n = 4)
L- gastric infusion, 1.56 g L
tap water
↑ secretion (media) (varied
time and dose effects)
↑ media (474% ± <20%)
↑ plasma (≈55% ± <20%
(SE))
↑ plasma (≈55% ± <20%
(SE))
↔plasma (ND)
↔ plasma (ND)
↔ plasma (ND)
↑plasma versus baseline (5g
only) (effect magnitude
unclear)
↔ plasma (ND)
90-min intraduodenal infusions 3.3 g or 9.9 g L
L- 0.3 g/kg (LBM) oral
L and I- 0.3 g/kg (LBM) oral
I- gastric infusion, 5 g or 10 g I
I- approximately 150 mM-230 mM I for 18 h
I- 50 mM intestinal infusions
Isotonic Control solution (glycine)
Water with Stevia
Water with Stevia
Suspension Control
Control
Baseline
↔ plasma (ND)
↔ plasma (active) (ND)
↔ plasma (active) (ND)
↔ plasma (ND)
↑ media (264% ± <20%)
↔ plasma (ND)
[38]
[77]
[77]
[68]
[75]
[76]
L
L
L
L
L
L
L
L/I
I
I
I
[75]
[74]
[74]
[76]
[37]
[37]
[68]
[67]
(continued on next page)
8
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
in opposition to past reports [55], hypothalamic LepR mRNA expression
was unchanged suggesting reduced leptin sensitivity (which also
appeared to correspond with adiposity) [8]. Differences between this
report and others may be explained by discrepancies in diet
composition. Interestingly, pigs given a low-protein diet exhibited
increased serum leptin which was reduced by the addition of BCAA at
various ratios, and similar trends in mRNA expression in adipose tissue
were also observed [59].
Table 3 (continued )
Treatment
Experimental Model
Dosing
Comparison
Response (GLP-1)
Reference
I
V
V
AA
AA
Healthy subjects (n = 12)
NCI-H716 cells
SD rats M (n = 4)
Healthy M (n = 16)
Healthy M (n = 16)
I- 0.3 g/kg (LBM) oral
V- approximately 44 mM-265 mM for 18 h
V- 50 mM intestinal infusions
AA Mixture- ID infusion, 2.1 kJ/min
AA Mixture- ID infusion, 6.3 kJ/min
Water with Stevia
Control
Baseline
Saline Control
Saline Control
[77]
[75]
[76]
[78]
[78]
AA
Healthy M (n = 16)
AA Mixture- ID infusion, 12.5 kJ/min
Saline Control
AA
AA Mixture- 306 kJ in orange juice
Maltodextrin 306 kJ in orange
juice
25 g glucose
WP
Adolescence w/obesity (n =
14)
Normal weight subjects (n =
12)
SD rats M (n = 30)
↔ plasma (active) (ND)
↔ media (ND)
↑ plasma (2.9 fold)
↔ plasma (ND)
↑ plasma (564 mmol ± 159
mmol)
↑ plasma (659 mmol ± 171
mmol)
↑ plasma (varied time
effects)
↔ plasma AUC (ND)
[60]
WP
SPF M Wistar rats (n = 12)
↑ plasma (≈20 pM ±≈5 pM
(SE))
↔ plasma (ND)
Protein
Protein- nutrient pre-load (50g)
↑ plasma (1.1 (AUC) ±1.6
(StDe))
[81]
[80]
↔ plasma (ND)
[80]
WP
Healthy subjects (n = 25)
↔ plasma (ND)
[44]
WP
Healthy subjects (n = 25)
WP- Breakfast custard w/either normal protein
(pro/carb/fat = 10/55/35 En%)
WP- Breakfast custard w/high protein (25/55/
20 En%)
50 g maltodextrin with or without
CAS
50 g maltodextrin with or without
CAS
Breakfast custard of soy or CAS
protein
Breakfast custard of soy or CAS
protein
↔ plasma (ND)
WP
Subjects w/overweight and/
or obesity and/or diabetes (n
= 16)
Healthy subjects w/
prediabetes (n = 15)
Healthy M (n = 15)
[44]
WP
WP- 18 g WP + 25 g glucose
25 g glucose
WP
Normal weight subjects (n =
12)
Healthy M (n = 20)
↔ plasma (ND) vs Soy, ↑ Δ
plasma (264 (AUC) ±135
(SE)) vs CAS
↔ plasma AUC (ND)
Protein- 3 kcal/min, ID infusion, 90-min
Saline Control
±112
[71]
WP
Healthy M (n = 12)
WP- 3 kcal/min ID infusion, 60-min
Saline Control
±106
[72]
WP
Healthy M w/obesity (n = 12)
WP- 1.5 kcal/min ID infusion, 60-min
Saline Control
±138
[72]
WP
Healthy M w/obesity (n = 12)
WP- 3 kcal/min ID infusion, 60-min
Saline Control
±136
[72]
WP
Subjects w/overweight (n =
39)
PPH (300 mL, 1024 kJ, 15 g PPH)
WP
Healthy subjects (n = 5)
WP
WP
M w/diabetes (n = 11)
F w/obesity (n = 8)
WP- Oral (beverage/shake), 300 mL, 1024 kJ,
% energy from pro/carbs/fat = 25/42/33 w/
150 mL water: WP (15 g WP)
WP- Oral, load of WP (8 g) plus glucomannan
(1 g) (0–3 h)
WP/WPH- 15 g (68 kcal)
WP- 45 g
↑ plasma (752 (AUC)
(SE)
↑ plasma (402 (AUC)
(SE)
↑ plasma (416 (AUC)
(SE)
↑ plasma (609 (AUC)
(SE)
↑ plasma (31.2pMol
±150.2 pMol)
Treatment
Experimental Model
Dosing
Comparison
Response (PYY)
Reference
L
L
L
Healthy M (n = 12)
Healthy M (n = 12)
Older F (n = 10)
Saline
Saline
Control (nothing)
↔ plasma (ND)
↔ plasma (ND)
↔ plasma (ND)
[37]
[37]
[40]
L
L
AA
Healthy F (n = 40)
Healthy M (n = 9–11)
Aged F (n = 10)
L- IDI, 0.15 kcal/min
L- IDI, 0.45 kcal/min
L- Oral (bar) (565 kJ) or gel (477 kJ); EAA (7.5 g, 40%
L-L)
L- Oral (bar), 2 g or 3 g L
L- 90-min IDI 3.3 g or 9.9 g L
EAA Gel- 478 kJ
I caloric bar (0 g)
I tonic Control solution (glycine)
Control (nothing)
[83]
[38]
[84]
WP
WP
SD rats M (n = 30)
SPF Wistar rats M (n
= 12)
WP- High protein 24% (wt/wt) of WP
WP- (1.1 kcal/g; 35% WP, 35% sucrose, 30% corn oil)
WP
Healthy subjects (n =
5)
Subjects w/
overweight (n = 39)
Low protein Control (14%)
NUTRALYS pea protein (1.1 kcal/g;
35% pea protein, 35% sucrose, 30%
corn oil)
Oral, load of CAS (8 g) plus
glucomannan (1 g)
PPH (300 mL, 1024 kJ, 15 g PPH)
↔ plasma (ND)
↔ plasma (ND)
↑plasma (≈10 pg/ml
± ≈22 pg/ml (SD))
↔ plasma (ND)
↔ plasma (ND)
↔ plasma (ND)
[73]
↔ plasma (ND)
[46]
↑plasma (≈25%
(AUC) ± ≈65% (SD))
↑plasma (≈22 pg/ml
±≈27 pg/ml (SD))
[82]
BCAA
WP
BCAA- (4.4 g) + 25 g glucose
WP- High protein 24% (wt/wt) of WP (HP-W)
or I flavone-free SP (HP-S)
WP- (1.1 kcal/g; 35% WP, 35% sucrose, 30%
corn oil)
WP- with 50 g maltodextrin
WP- with 50 g maltodextrin
WP
F w/obesity (n = 8)
WP- Oral, load of WP (8 g) plus glucomannan (1 g) (0–3
h)
WP- Oral (beverage/shake), 300 mL, 1024 kJ, % energy
from pro/carbs/fat = 25/42/33 w/150 mL water: WP
(15 g WP)
WP- 45 g
WP
Aged F (n = 10)
WP- 275 kJ
WP
Control (low protein (14%))
NUTRALYS pea protein (1.1 kcal/
g; 35% pea protein, 35% sucrose,
30% corn oil)
Water
Oral, load of CAS (8 g) plus
glucomannan (1 g)
Flavored water (<1 kcal)
43 g maltodextrin
43 g maltodextrin
Control (nothing)
9
↑ plasma at 90 min (0.95
pMol ±1.08 (StDe?))
↔ plasma (ND)
↑ plasma (≈20% (AUC) ±
≈55% (StDe))
[78]
[41]
[79]
[42]
[79]
[46]
[73]
[64]
[82]
[60]
[42]
[84]
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
Additionally, the effects of whey protein have also been investigated.
Zhou et al. performed a study comparing whey versus soy protein on
food intake and hormonal levels in 30 male SD rats [60]. Rats were given
either control diet (consisting of the AIN-93 M diet), or two different
protein diets: high protein with whey (HP-W) comprised of the control
diet with half of the starch replaced with whey protein (14% egg albu­
min, 24% WP), or the high-protein content control diet (HP-S),
protein-matched to the HP-W diet, but whey protein was replaced with
isoflavone-free soy protein [60]. Food intake was measured throughout
the experiment for 10 weeks, and trunk blood samples were obtained
[60]. Although food intake was significantly decreased in the HP-W
group when compared to both HP-S and the control, there was no sig­
nificant difference in plasma leptin concentrations [60]. In a different
study focusing on the effects of whey protein versus leucine adminis­
tration, 20-week-old male C57BL/6 mice were individually housed and
split into three groups, each given a HFD (20% wt/wt fat) with either
adequate protein (control; 10% wt/wt), high protein (HP; 50% wt/wt),
or leucine (control +6% L-leucine wt/wt) [61]. Mice were provided ad
libitum access to feed for 20 weeks, with food intake recorded daily [61].
Total RNA from liver was assessed to determine leptin mRNA expres­
sion, as well as the expression of various genes involved in liver and
white adipose signaling [61]. Leptin mRNA expression decreased in the
HP group only when compared to control and leucine groups, whereas
food intake decreased in both the HP and leucine groups when compared
to the control, supporting the potentially satiating effects of both whey
protein and leucine possibly through increased leptin sensitivity [61].
In another study, 12-week-old male C57BI/6 mice were fed a high-fat
diet of specially formulated chow (pro/carb/fat = 16/44/40%; 3.86
kcal/g) for 20 weeks [62]. Mice with the highest weight gain were
considered to have diet-induced obesity and were randomized into 5
varied diets for 8 weeks: control (HFD), and 4 high-protein diet treat­
ment groups (pro/carb/fat = 30/30/40%) containing ~15% of either
whey, soy, milk, or red-meat protein [62]. Food intake was measured,
and energy intake was calculated daily for 8 weeks [62]. Blood samples
were analyzed for plasma leptin, and no significant difference between
the five groups was observed [62]. Additionally, total energy intake over
the 8-week study was significantly lower for the whey (− 9%) and
red-meat (− 8%) protein groups when compared to the control, soy, and
milk protein groups [62].
In a similar study, male SD rats given ad libitum access to the HFD
(pro/carb/fat = 20/20/60%) for 13 weeks were then divided into 8
treatment groups, four of which remained on the HFD, while the
remaining four groups were switched to a normal fat diet (NFD, pro/
carb/fat = 20/63/17%) for eight weeks [63]. During the eight weeks,
groups were given one of four diets matched for protein content (20%)
including casein (control), corn gluten peptide, leucine, or BCAA
(valine:isoleucine:leucine = 1.25:1:4.04) [63]. The body weight and
food intake of the rats were measured weekly, and no significant dif­
ference was found in the BCAA or leucine group for either NFD or HFD
when compared to the respective controls [63]. Following the 8-week
experiment, rats were sacrificed, and their plasma was analyzed for
leptin content, however no significant effect was observed for either
leucine, or BCAA regardless of base diet [63]. Furthermore, male sub­
jects with diabetes were assessed for their acute response to either a
whey protein, hydrolyzed whey protein, or control nutrient pre-load
prior to mixed-nutrient meal challenges displayed similar responses in
leptin levels [64]. Comparable findings were obtained in a longer study
examining whey versus collagen supplements in females with obesity,
during which after 8 weeks of supplementation, no statistical difference
was observed in leptin concentrations [65]. Taken together, the effect of
leucine, BCAA, and/or protein type on leptin levels is unclear, although
from these data it appears as though leucine, in particular, may activate
the secretion of and/or promote the sensitivity to leptin, however this
too is unclear given not every report assessed leptin receptor content
(Table 2). Additionally, it should be noted that of the studies identified
in this report, only cell culture or animal models treated with leucine
were identified as influencing leptin levels. Of the animal studies sum­
marized herein, 4 of 10 studies showed improved leptin sensitivity or
circulating levels following leucine treatment. Moreover, 1 study in mice
showed increased leptin levels following BCAA treatment of mice, while
treatment of protein-deficient piglets with BCAA showed reduced leptin
levels. Lastly, WP offered no apparent benefit on circulating leptin in
either mice or rats. Thus, additional research in humans is required to
render a conclusion about individual and mixtures of BCAA on circu­
lating leptin levels in various populations.
3.3. Effect of BCAA on other select regulators of satiety
CCK- Mechanistically, the effect of amino acids on CCK has been
investigated. For example, leucine, isoleucine, and combination BCAA
(but not valine) significantly increased mRNA expression of Cck in
porcine proximal jejunum following treatment in a time- and dosedependent manner [66]. Yet, in a human trial, 12 healthy-weight
males given leucine for 90 min at either 0.15 kcal/min, 0.45 kcal/min
or saline control, leucine administration had no effect on plasma CCK
levels in comparison to the control saline solution [37]. Similarly,
another randomized, double-blind, crossover trial comprised of 10
normal weight and 10 subjects with obesity assessed the effects of
intragastric infusions of either leucine, or varied levels of tryptophan on
CCK, and found leucine had no effect on CCK versus the tap water
control, however tryptophan significantly increased CCK versus both tap
water and leucine [67]. In another randomized double-blind control
study, 12 healthy male subjects received either 5 g or 10 g leucine, or a
control via intragastric infusion, followed by a mixed nutrient meal
[68]. The study also showed no change in CCK levels [68]. Conversely,
some studies have shown an effect of BCAA on CCK. For example,
Steinert et al. retrospectively analyzed the effect of individual amino
acids (including leucine) from four previous trials on CCK following
90-min intraduodenal amino acid infusions, which was increased
following leucine infusion versus glycine (but statistically unchanged
versus tryptophan or phenylalanine) [38]. Like the findings from Stei­
nert et al. [38], healthy male subjects given leucine via 90-min intra­
duodenal infusion displayed increased CCK concentrations at 90-min
versus isotonic saline controls [69]. And although not as extensively
studied as leucine, spares data is available for other BCAA. Like leucine,
isoleucine and combination BCAA (but not valine) significantly
increased mRNA expression of Cck in porcine proximal jejunum [66].
Additionally, the effect of varied levels of valine (indicated by stan­
dardized ileal digestible (SID) valine to lysine ratios) on mRNA expres­
sion of CCK in both gastric and duodenal tissue of piglets was assessed,
and valine was associated with reduced gastric CCK expression while
duodenal expression was unchanged [39]. Moreover, intraduodenal
infusion of valine did not alter either CCK levels or food intake in healthy
lean males [70].
Similarly, protein has been assessed for effects on CCK. For example,
SD rats given either a high protein (whey or soy) diet versus a lower
protein (control) diet exhibited no change in CCK levels [60]. Similar
results were obtained by Overduin et al. in a study assessing changes in
plasma CCK following the consumption of whey or pea protein in 10
male SPF Wistar rats (treatment details described in Table 3 or above
within the Ghrelin response section), however whey protein resulted in
no change in CCK compared to pea protein [42].
Additionally, a study comparing pure protein to a saline control via
intraduodenal nutrient infusions in healthy male volunteers showed that
protein significantly increased levels of CCK over the course of 90 min
post-infusion [71]. A similar study by the same group also showed
elevated CCK in males with obesity following intraduodenal hydrolyzed
whey protein infusions, occurring in a dose-dependent fashion [72]. And
lastly, in healthy subjects, 8 g of WP had no effect on CCK levels [73]. Of
the available human trials, leucine and BCAA may increase CCK levels,
with 4 of 5 trials showing leucine may offer some effect and 3 out of 6
trials suggesting whey protein may increase CCK.
10
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
GLP-1- Dietary protein has also been shown to increase plasma levels
of GLP-1 [71]. Mechanistically, a study in STC-1 intestinal cells showed
that leucine treatment upregulated GLP-1 secretion in a time and
dose-dependent fashion with changes in GLP-1 production seen as early
as 12 h and persisted until 36 h post-treatment [74]. Another study
investigating the effect of individual BCAA on NCI-H716 cell mRNA
expression of GLP-1 found both leucine at 1.5–2% (approximately 114
mM-150 mM) significantly increased mRNA expression of GLP-1
following 18 h of treatment, while valine at similar concentrations
failed to invoke any significant response [75]. In addition to their
mechanistic studies, Xu et al. also showed male C57BL/6J mice fed
either chow or high-fat diets followed by intragastric administration of
leucine (3.5 mmol/kg for 6 days) had significantly increased plasma
GLP-1 in both diet conditions, compared with saline control (which was
also reproduced upon leucine IP injection) [74]. In SD rats perfused with
leucine did not alter GLP-1 levels [76]. In 12 healthy-weight males given
leucine for 90 min at either 0.15 kcal/min, 0.45 kcal/min or saline
control, leucine administration had no effect on plasma GLP-1 levels in
comparison to the control saline solution [37]. In a different randomized
double-blind control study, 12 healthy male subjects received either 5 g
or 10 g leucine, or a control via intragastric infusion, followed by a
mixed nutrient meal [68]. The study showed groups were not different
in GLP-1, however leucine at 5 g displayed a significant increase in
GLP-1 over time [68]. Another randomized, double-blind, crossover trial
with 10 normal weight and 10 subjects with obesity found no effect of
intragastric infusions of leucine on active GLP-1 [67]. And like CCK,
Steinert et al. retrospectively analyzed the effect of individual amino
acids on GLP-1 following 90-min intraduodenal amino acid infusions
and found no change in GLP-1 following leucine treatment [38]. Simi­
larly, healthy male and female subjects given either leucine, isoleucine,
or a combination thereof, none of the treatment conditions altered
active GLP-1 [77].
Mechanistically, other amino acids have been studied for effects on
GLP-1. A study investigating the effect of individual BCAA on NCI-H716
cell mRNA expression of GLP-1 found isoleucine at 2–3% wt/vol
(approximately 150 mM- 230 mM) significantly increased mRNA
expression of GLP-1 following 18 h of treatment [75]. Despite these
findings, in vivo findings show less of an effect of isoleucine. For
example, SD rats perfused with individual isoleucine caused only
insignificant increases in GLP-1 levels [76]. Similarly, human subjects
given isoleucine either alone or in combination with leucine did not alter
active GLP-1 [77]. In line with these observations, a randomized
double-blind control study with 12 healthy male subjects received either
5 g or 10 g isoleucine or a control via intragastric infusion and found that
isoleucine also had no effect on GLP-1 [68]. Interestingly, while valine
failed to invoke an in vitro response in GLP-1 mRNA expression in
NCI-H716 cells (like leucine or isoleucine) [75], valine was shown to
increase GLP-1 levels in SD rats [76].
Like amino acids, combinations of amino acids and protein have also
been studied for effects on GLP-1. For example, SPF Wistar rats given
whey protein showed no change in GLP-1 compared to pea protein [42].
Conversely, higher rates of intraduodenal protein infusion in healthy
males was shown to increase GLP-1 levels [78]. Similarly, a mixture of
EAA including leucine was examined in adolescents with obesity. The
study found increased GLP-1 response following supplementation versus
the control (maltodextrin) [41]. However, in a randomized cross-over
study in which normal-weight subjects received either whey protein or
various amino acid mixtures with 25 g glucose, neither whey protein nor
the varied BCAA mixtures significantly altered the percent change in
GLP-1 [79]. However, it is important to note that baseline, GLP-1 levels
were significantly greater in the BCAA group versus the reference group
prior to beverage consumption, which may have altered the relative
change for each group [79]. Conversely, in male SD rats given whey
protein rather than an amino acid mixture, GLP-1 increased versus the
lower protein chow control, but not when compared to an equal protein
soy group [60]. However, in a study with either healthy or subjects with
diabetes, subjects received drinks containing 50 g of maltodextrin alone,
or with 50 g of either whey protein isolate, or sodium caseinate in a
randomized, double-blind, cross-over fashion [80]. There was no effect
of either protein source on plasma GLP-1 versus solely maltodextrin
[80]. Trico et al. examined the effect of a high-protein nutrient preload
on GLP-1 response following an oral glucose tolerance test in subjects
with type 2 diabetes, and found protein pre-load increased GLP-1 and
that plasma leucine showed the greatest relationship with GLP-1
response [81], although it should be noted that water served as the
respective control. Moreover, the Veldhorst study described earlier in
the ghrelin section, subjects received a standardized custard breakfast
containing either whey, casein, or soy as the single source of protein. It
was found that subjects that consumed whey protein exhibited signifi­
cantly greater active GLP-1 versus both soy and casein [44]. Moreover,
in 39 subjects considered overweight (19 M/20 F, 18-60 years-old) that
consumed 4 varied shakes (1024 kJ, pro/carb/fat = 25/42/33%) in a
randomized order, subjects displayed elevated GLP-1 levels in the WP
versus PPH group [46]. Additionally, 8 g of WP elevated GLP-1 levels of
healthy subjects [73]. Conversely, in another study, male subjects with
type 2 diabetes were assessed for acute response to a whey protein or
hydrolyzed whey protein, both of which displayed similar response in
GLP-1 levels as control [64]. However, WP increased GLP-1 in females
with obesity [82]. Together, only 1 out of 5 human trials showed leucine
influenced GLP-1, however 8 out of 13 human trials using blends of
amino acids or protein increase GLP-1 levels.
PYY- Lastly, dietary protein has also been shown to increase plasma
PYY [71]. For example, Steinert et al. retrospectively analyzed the effect
of individual amino acids various hormones including PYY following
90-min intraduodenal amino acid infusion and found PYY levels
remained unchanged in leucine versus glycine, and were lower in
leucine versus tryptophan and phenylalanine [38]. Furthermore, in a
randomized, double-blind placebo-controlled study, Bolster and col­
leagues assessed the effect of a low-protein nutrition bar fortified with 2
g of leucine, versus an isocaloric control, on plasma PYY, which
remained unaltered [83]. Another study consisting of older females
(68.4 ± 4.5 years) given either a bar (565 kJ) or gel (477 kJ), rich in
essential amino acids (EAA) (7.5 g, 40% L-leucine), demonstrated un­
changed PYY levels versus control (consumed nothing) [40]. SPF Wistar
rats given whey protein showed no change in PYY compared to pea
protein [42]. Conversely, 45g of WP increased PYY in females with
obesity [82]. Similarly, aged females given either WP, an EAA gel, or
nothing (as control), levels of PYY were significantly higher in both
treated versus control groups [84]. Likewise, 39 subjects considered
overweight (19 M/20 F, 18-60 years-old) that consumed 4 varied shakes
(1024 kJ, pro/carb/fat = 25/42/33%) in a randomized order displayed
elevated PYY levels in the WP versus PPH group [46]. Conversely, in
healthy subjects, 8 g of either WP or casein induced no change in PYY
[73]. Of the 4 human trials identified by this report, leucine had no
effect on PYY. However, amino acid mixtures or protein increased PYY
levels in 3 out of 5 human trials. Thus, taken together, it appears that
leucine alone may increase CCK levels but does not appear to have the
same effect on GLP-1 or PYY. Conversely, amino acid mixtures or protein
appear to increase the levels of CCK, GLP-1, and PYY more reliably,
suggesting individual amino acids may be insufficient in eliciting some
of the satiating response of protein.
3.4. Effect of BCAA on energy intake
The effect of protein on food intake has been previously investigated,
and it is generally noted that higher protein diets may reduce hunger
and total energy intake. However, type of protein appears to impact the
satiating effect of the protein, with whey protein among the most sati­
ating [85]. Because whey protein is higher in BCAA than other similar
protein sources, BCAA represent one possible set of constituents
responsible for varied satiating effects of whey versus other protein.
Heeley et al. previously summarized the effects of centrally
11
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
administered individual BCAA on food intake, and noted leucine
consistently resulted in reduced food intake, while valine and isoleucine
did not (although isoleucine and valine are far less studied than leucine)
[86]. In fact, the effects of leucine on food intake and satiety have been
examined using several experimental models. For example, a study
consisting of male C57BL/6J mice given leucine in drinking water
(1.5%) showed an increase in food intake on chow diets, which was not
observed when mice received a HFD [53]. In a similar study, C57BL/6J
mice also given leucine in drinking water displayed increased acute food
intake, while chronic leucine administration did not alter intake
regardless of HFD or LFD [87]. Interestingly, in male C57BL/6J mice
given leucine with and without leptin, only the combination of leucine
and leptin reduced acute refeeding [52]. Mao et al. also examined the
effect of leucine on food intake in both C57BL/6 and ob/ob mice,
demonstrating that supplementing with dietary leucine (3%) had no
effect on food intake in either mouse type [51].
Conversely, some findings suggest leucine may suppress appetite and
food intake. For example, Noasch et al. sought to determine the effects of
whey protein or supplemental leucine in combination with low fat diets
on mice [88]. C57BL/6 mice were divided into three treatment groups;
normal protein diet (AP, 20% protein), a high protein diet (HP, 50%
whey protein), or a leucine supplemented diet that used the AP diet but
matched the leucine concentration found in the high protein diet. The
experiment lasted for a total of 14 weeks and food intake was calculated
weekly. Results show leucine supplementation was the most effective in
reducing food intake followed closely by the HP diet [88]. These find­
ings have also been shown using a similar experimental model (C57BL/6
mice) and treatment conditions [61]. Drgonova et al. also sought to
determine the effects of leucine on food intake, metabolism, and
vulnerability to obesity using a SLC6A15 knockout (KO) mouse model.
Mice were given ad libitum access to water and chow for 9 weeks after
which water was supplemented with 1.5% leucine for four days. Leucine
significantly decreased consumption of chow in WT males but not in KO
males [89]. Leucine (and increased dietary protein) has also been shown
to reduce food intake in mice in part via the nucleus of the solitary tract
(NTS) signaling [90]. The effects of leucine have also been investigated
in mice using medio-basal hypothalamus infusion [91]. Interestingly,
leucine reduced food intake, as well as the size and number of meals
(effects that were not observed in valine-treated mice) [91]. These ob­
servations were also made using SD rats [91]. Similarly, intra­
cerebroventricular infusion with leucine reduced food intake in SD rats
given normal [92], or low-protein diets [92], and appears to function in
a time- [93] and dose-dependent fashion [94]. However, in opposition
to intracerebroventricular infusion, a leucine-supplemented diet (4.5%)
increased food intake in Wistar rats [57]. Other studies using rat models
have largely shown no effect of leucine supplementation on acute [95]
or weekly food intake [56,63,96] which was not influenced by a HFD
[55,63].
Leucine has also been investigated for its effect on hunger and food
intake in humans. In healthy males given an intraduodenal infusion of
leucine, decreased energy intake for the highest infusion rate (0.45 kcal/
min) but not lower rates were observed [37]. Similar studies using
intraduodenal infusions of leucine also showed no change in prospective
food consumption or buffet meal intake [38], and comparable results
have been obtained using a gastric infusion [68]. Similarly, using a
crossover design with healthy subjects classified as overweight, Traylor
et al. demonstrated that a leucine-enriched bar could suppress appetite
(indicated by VAS scores) following a low-protein breakfast to a similar
extent as a high-protein breakfast [97]. Additionally, leucine given to
healthy subjects via 90-min intraduodenal infusion did not alter VAS
scores related to hunger or buffet meal consumption [69]. Interestingly,
some observations have shown reductions in indicators of appetite
following the consumption of food fortified with essential amino acids
[40] but not leucine [83].
Unlike leucine, valine and isoleucine are far less investigated for
their effects on satiety and food intake. From the available literature, it
appears that neither isoleucine [68,98] nor valine [70,98] have any
substantial effect on food intake. Mixtures of amino acids which include
BCAA have been explored using various models. In rats, Bong et al. used
a 5.6% BCAA-supplemented feed and found unaltered weekly food
intake in comparison to a casein control [63]. Similar results were ob­
tained using an identical experimental protocol with a HFD [63].
Additionally, Solon-Biet et al. recently thoroughly investigated the effect
of varied BCAA content of feed on food intake, and reported that mice
consuming the 200% BCAA diet exhibited significantly higher food
intake, fat mass, and body weight versus other diets (100% BCAA con­
tent (reference food), 50%, or 20% BCAA content) [8]. This report is of
special significance as it identified that the disparate energy intakes and
related comorbidities between groups were attributable to elevated ra­
tios of BCAA:non-BCAA (or a set of lacking amino acids), and that weight
gain could be resolved through the addition of lacking amino acids
(specifically, tryptophan) or through concurrent energy restriction [8].
This finding is meaningful as it highlights several additional complex­
ities in the study of BCAA on satiety and food intake, as disparities in
diet-type, protein source, amino acid/protein composition and type,
feeding/intervention duration, and other factors are likely influencing
outcomes, and may be responsible for varied outcomes between studies.
And in humans, a mixture of essential amino acids including leucine was
assessed for its effect on satiety in adolescents with obesity, which
showed increased satiety and reduced hunger following supplementa­
tion versus control, though total energy consumed at ad lib dinner was
not different between the two groups [41].
Unlike valine and isoleucine, the effect of the type of protein has
been more extensively studied. Whey protein has also been studied in
animal models, and has been shown to reduce energy intake in mice [62]
and reduce food intake in rats [60]. However, mice that consumed food
with protein from either whey protein or whey protein hydrolysate had
similar energy intakes to mice fed a diet with casein as the protein source
[99]. This observation was true of both low- and high-fat fed animals
[99]. In humans, whey protein has also been shown to reduce food
intake and reduce feelings of hunger. For example, Hall et al. sought to
determine the effects of whey and casein (48 g) on food intake and
hunger. Subjects received liquid whey or casein preloads after con­
sumption of a normal breakfast. Subjects were then offered a buffet meal
and macronutrient intake was calculated. The results show whey had a
greater effect on lowering energy intake when compared to casein
[100]. Pal et al. examined the effects of protein-containing meals on
variables including appetite and energy intake in lean men [101]. The
subjects completed a randomized, single-blind, crossover study in which
they were treated with 4 different protein meals, with a one-week
washout period between each treatment. Treatments were liquid
meals containing either tuna, turkey, whey protein, or egg albumin each
weighing 600 g. Four hours post-consumption, subjects were offered a
buffet meal which was consumed ad libitum. Results showed whey had
the greatest effect on reducing food intake [101]. Giuseppe et al.
examined the appetite-controlling effects of whey protein using a cross
over design with a 1-week wash out period. The treatment was 8 g of
either whey protein or casein, which was administered orally. The study
found no differences in ratings of appetite between the two groups [73].
Furthermore, in a two-part, randomized, single-blind, crossover study
consisting of 39 subjects considered overweight (19 M/20 F, 18-60
years-old), Diepvens et al. provided subjects with one of four shakes in
a randomized order, and appetite questionnaires were completed at 30,
60, 90, 120, and 180 min post-consumption. At 180 min, subjects were
provided with ad libitum access to 300 mL of water and a lunch con­
sisting of Turkish bread with egg salad. Subjects were instructed to eat
until comfortably satiated. There was no difference in food intake at
lunch, or in hunger between the 4 groups, nor was there a significant
difference found in satiety, feeling of fullness, or appetite between the
WP and PPH groups [46]. Similarly, healthy subjects given 10g of WP
displayed no change in VAS hunger scores [47]. Conversely, aged fe­
males given WP exhibited significantly reduced levels of appetite versus
12
Human Nutrition & Metabolism 30 (2022) 200168
B. Lueders et al.
Table 4
Summary of the effect of BCAA on appetite and food intake. Abbreviations: AA, amino acid mixture; CPE, cocoa polyphenolic extract; EAA, essential amino acids;
F, female; FR, food restriction; HFD, high-fat diet; HP, high protein; ID, intraduodenal infusion; I, isoleucine; L, leucine; M, male; LFD, low-fat diet; ND, no difference;
OB, obese; PPH, pea protein hydrolysate; SD, Sprague-Dawley; StDe, standard deviation; SE, standard estimate of the mean; SP, soy protein; SPF, specific pathogenfree; SPI, soy protein isolate; WP, Whey protein/Whey protein isolate; WT, weight; V, valine; V:LYS, valine:lysine ratio. Notes: effects noted within “Food Intake/
Appetite” column are reported as raw values (if available) or as estimates (indicated by ≈) of percent change from control mean ±the variability for the treated group.
“?” next to StDe indicates the type of variability presented was unclear.
Treatment
Experimental Model
Dosing
Comparison
Food Intake/Appetite
Reference
L
L
C57BL/6J mice (n = 9–11)
C57BL/6J mice (n = 9–11)
L- Drinking water 1.5% (wt/vol)
L- Drinking water 1.5% (wt/vol)
↔ Acute refeeding (ND)
↔ Acute refeeding (1, 2, 4, and 8 h)
[52]
[52]
L + Leptin
C57BL/6J mice (n = 9–11)
C57BL/6J M mice (13–15 g;
n = 20), leptin-deficient ob/
ob M mice (30–42 g; n = 24)
C57BL/6J Mice M (n = 5)
C57BL/6J Mice M HFD (n =
5)
C57BL/6J mice (n = 20)
↓ Acute refeeding (1, 2, 4, and 8 h) (≈18% at
8hr ± <10% (SE))
↔ Food intake (ND)
[52]
L
L- Drinking water 1.5% (wt/vol) + IP
injection (5 mg/kg)
L- Non-purified rodent diet (13.42 MJ/kg)
with 3% L-L added diet
L- Drinking water 1.5% (wt/vol)
L- Drinking water 1.5% (wt/vol)
Chow/water
Chow/water and
vehicle
Chow/water and
vehicle
Non-purified rodent diet
(13.42 MJ/kg) with
2.04% L-alanine
Chow (regular water)
HFD (regular water)
↑ Daily food intake (8.4% ± <10% (SE))
↔ Daily food intake (ND)
[53]
[53]
L- oral (gavage) 0.5 M L in water 2 for days
Water (oral gavage)
[87]
C57BL/6 Ob/Ob mice (n =
7)
C57BL/6J mice LFD (n =
9–10)
C57BL/6J mice HFD (n =
9–10)
C57BI/6 mice M (n =
10–11/group)
C57BL/6 mice M (n = 9–11)
Congenic SLC6A15, wild
type mice (n = 13–14)
Congenic SLC6A15 knockout mice (n = 13–14)
C57BL/6 mice M (n =
10–12)
L - Drinking water 0.15 M for 10 days
Water
↑ Acute daily energy intake (kcal) (≈22% ±
118 ± <10% (SE))
↔ Daily energy intake (kcal) (ND)
L - Drinking water 0.15 M for 6 weeks
Water LFD
↔ Daily energy intake (kcal) (ND)
[87]
L - Drinking water 0.15 M for 6 weeks
Water HFD
↔ Daily energy intake (kcal) (ND)
[87]
Adequate protein + L - (20% WP + L)
Adequate protein only
[88]
Adequate protein + L - (10% WP + L)
L - Drinking water 1.5% (wt/vol) for 9
weeks
L - Drinking water 1.5% (wt/vol) for 9
weeks
L/KIC- mediobasal hypothalamus infusion
Adequate protein only
Chow (regular water)
↓ Food (24 g ± 6 (SE)) and energy (31 MJ ±
0.09 (SE)) intake
↓ Food (0.58 MJ ± 0.22 (SE)) intake
↓ Daily energy intake (≈10% ± <10% (SE))
M/↔ Daily energy intake F (ND)
↔ Daily energy intake (kcal) M/F (ND)
[91]
L
SD rats M (n = 10–12)
L/KIC- mediobasal hypothalamus infusion
Artificial cerebrospinal
fluid
L
SD rats M (n = 7–9)
PBS Vehicle
L
SD rats M (n = 15–20)
L - Intracerebroventricular infusion 1, 3, or
10 μg
L - Intracerebroventricular infusion 10 μg
L
SD rats M LP (n = 10)
L - Intracerebroventricular infusion 10 μg
Saline control
L
L - Intracerebroventricular infusion 1.1 μg
Vehicle
L
Djungarian hamsters M (n
= 13–16)
Wistar rats aged (n = 89)
L -supplemented diet (4.5%) for 6 months
L
L
L
L
SD rats M HFD (n = 7–8)
SD rats M (n = 8)
SD rats M HFD (n = 8)
Wistar Rats M (n-12)
L
SD rats M HFD (n = 48)
L
Wistar rats (n = 5–6)
Djungarian hamsters M (n
= 5)
Leghorn chicks (n = 15–17)
↔ Weekly food(g) or energy (kcal) intake
(ND)
↔ Daily food intake (g) (ND)
↓ Food intake (g)
[55]
L
L
L - Diet supplemented with 5%
L - Diet supplemented with 3.6%
L - Diet supplemented with 3.6%
L - Intragastrically administered 6.7 mmol/
kg
L - Diet supplemented with 1.5%, 3.0%, or
4.5%
L - Diet supplemented with 1.11%
L - standard diet + 15%
Control diet (accounts
for AA and caloric
content of L with lysine)
Control diet
CAS (control) diet
CAS (control) diet
Water
↓ Food intake (varied time effects), meal size
(varied time effects), and meal number
(varied time effects),
↓ Food intake (varied time effects), meal size
(varied time effects), and meal number
(varied time effects)
↓ Acute food intake (≈64% ± <10%) in 10 μg
but ↔ in 1 or 3 μg (ND)
↓ Acute food intake (≈30% ± <20% (?)) in
20%
↓ Acute food intake (≈25% ±<20% (?)) in
10%
↔ Food intake (g) at 4 h (ND) and ↓ food
intake 24hr (≈30% ± <20% (SE)
↑ Weekly food intake (≈20% ± <10% (SE))
at week 2 with ↔ weekly food intake (g)
weeks 4–22 (ND)
↔ Weekly food intake (ND)
↔ Weekly food intake (g) (ND)
↔ Weekly food intake (g) (ND)
↔ Acute refeeding (1hr) (ND)
↑ Acute food intake (g)
[98]
L
Broiler chicks
Healthy M (n = 12)
L
Older F (n = 11)
Oral, bar (565 kJ); EAA (7.5 g, 40% L-L)
Control (nothing)
L
Older F (n = 11)
Oral, gel (477 kJ); EAA (7.5 g, 40% L-L)
Control (nothing)
L
Healthy M (n = 11)
L
Healthy M (n = 11)
L
Healthy F (n = 40)
L - 90-min intraduodenal infusions 3.3 g or
9.9 g L
L - 90-min intraduodenal infusions 3.3 g or
9.9 g L
L - 2 g or 3 g, oral, bar
Isotonic control solution
(glycine)
Isotonic control solution
(glycine)
Isocaloric bar (0g)
↑ Acute food intake (g) 0.15 μmol and ↔ or
1.5 μmol
↓ energy intake (kcal) for 0.45 kcal/min L and
↔ for 0.15 kcal/min ↔ Food amount (g)
consumed for either group
↓ Appetite (23 mm ± 19 (StDe)), ↔ energy
intake (ND)
↓ Appetite (13 mm ± 17 (StDe)), ↔ energy
intake (ND)
↔ VAS prospective food consumption (mm)
(ND)
↔ Buffet intake (kcal) (ND)
[102]
L
L - Intracerebroventricular infusion
50–200 μg
L - Intracerebroventricular infusion 0.15
μmol or 1.5 μmol
L - 0.15–0.45 kcal/min, ID infusion
L
L
L
L
L
L
L
L
L
L
L
Chow (regular water)
Artificial cerebrospinal
fluid
Saline control
HFD-only
Control diet
Standard diet switch to I
L -rich diet
Saline control
Saline Control
Saline Control
[51]
[87]
[61]
[89]
[89]
[91]
[94]
[92]
[92]
[93]
[57]
[56]
[63]
[63]
[95]
[96]
[93]
[37]
[40]
[40]
[38]
[38]
[83]
(continued on next page)
13
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
Table 4 (continued )
Treatment
Experimental Model
Dosing
Comparison
Food Intake/Appetite
Reference
L
L
Healthy M (n = 12)
Healthy M (n = 16)
L - gastric infusion, 5 g or 10 g
L – intraduodenal infusion, 0.45 kcal/min
(41 kcal)
Suspension Control
Isotonic saline
L
Healthy subjects (n = 8)
Low-protein breakfast
IL
IL
Healthy M (n = 12)
Leghorn chicks (n = 12–16)
Suspension Control
Saline control
↔ Acute energy intake (kcal) (ND)
↔Acute food intake (g) (ND)
[68]
[98]
V
Leghorn chicks (n = 10–14)
Saline control
↔Acute food intake (g) (ND)
[98]
V
Healthy M (n = 12)
L – enriched bar, 1.5g with low-protein
breakfast
I/L - gastric infusion, 5g or 10g I L
I/L- Intracerebroventricular infusion
50–200 μg
V - Intracerebroventricular infusion
50–200 μg
V - 90-min intraduodenal infusions 9.9 g
↔ VAS Hunger/fullness/desire to eat/
prospective food consumption (mm) (ND)
↔ Acute energy intake (kcal) (ND)
↔ Buffet intake (kcal) (ND), ↔ VAS hunger/
fullness/desire to eat/prospective food
consumption (mm) (ND)
↓ VAS hunger/desire to eat, ↑ VAS fullness
Saline control
[70]
BCAA
C57BL/6J mice (n = 16–18)
BCAA- Varied (50%)
BCAA
C57BL/6J mice (n = 16–18)
BCAA- Varied (100%)
BCAA
C57BL/6J mice (n = 16–18)
BCAA- Varied (200%)
BCAA
BCAA
AA
BCAA- Diet supplemented with 5.6%
BCAA- Diet supplemented with 5.6%
AA Mixture- 306 kJ in orange juice
AA
SD rats M (n = 8)
SD rats M HFD (n = 8)
Adolescence w/obesity (n
= 14)
Healthy M (n = 16)
AA Mixture- ID infusion, 2.1 kJ/min
Normal diet with 20%
normal BCAA
Normal diet with 20%
normal BCAA
Normal diet with 20%
normal BCAA
CAS (control) diet
CAS (control) diet
Maltodextrin 306 kJ in
orange juice
Saline control
AA
Healthy M (n = 16)
AA Mixture- ID infusion, 6.3 kJ/min
Saline Control
AA
Healthy M (n = 16)
AA Mixture- ID infusion, 12.5 kJ/min
Saline Control
AA
Protein
Aged F (n = 10)
SD rats M (n = 7–9)
EAA Gel- 478 kJ
Protein- 20% of diet
Control (nothing)
Protein- 10% of diet
Protein
SD rats M (n = 7–9)
Protein- 20% of diet
Protein- 10% of diet
Protein
Protein
WP
SD rats M (n = 12)
SD rats M (n = 12)
C57BL/6 Mice M HFD (n =
9–10)
Low protein (10%) ±L
Protein (20%) of diet ± L
WP- with standard HFD
Protein- 10% of diet
Protein- 20% of diet
HFD only (control)
WP
WP- with standard HFD
HFD with Soy
WP as LFD diet protein source
CAS as LFD diet protein
source
CAS as LFD diet protein
source
CAS as HFD diet protein
source
CAS as HFD diet protein
source
Control and soy protein
↔ Total energy intake (kcal) (ND)
[99]
↔ Total energy intake (kcal) (ND)
[99]
↔ Total energy intake (kcal) (ND)
[99]
WP
C57BL/6 Mice M HFD (n =
9–10)
C57BL/6 Mice M LFD (n =
5–6)
C57BL/6 Mice M LFD (n =
5–6)
C57BL/6 Mice M HFD (n =
5–6)
C57BL/6 Mice M HFD (n =
5–6)
SD rats M (n = 30)
↔ Acute energy intake (kcal), ↔ VAS hunger/
fullness/desire to eat (mm) (ND)
↔energy intake (kJ/day) vs 100% and 20%
(ND)
↔energy intake (kJ/day) vs 50% and 20%
(ND)
↑ energy intake (≈10 kJ/day) vs 100%, 50%,
and 20%
↔ Weekly food intake (g) (ND)
↔ Weekly food intake (g) (ND)
↓VAS hunger (varied time effects), ↑satiety
(mm) (varied time and dose effects)
↔ Acute energy intake (kJ) (ND) ↔ and food
(g) (ND)
↓ Acute energy intake (kJ) (669 kJ ± 523 kJ)
and food (g) (ND) (152 g ± 118 g)
↓ Acute energy intake (kJ) (1359 kJ ± 502
kJ) and food (g) (252 g ± 107 g)
↔composite appetite score (ND)
↓ Cumulative food intake (g) weeks 3–7
(varied time effects)
↓ Food intake (g) days 2–7 (varied time
effects)
↔ Average daily food intake (g) (ND)
↔ Average daily food intake (g) (ND)
↓ Weekly energy intake (kcal) (varied time
effects), ↓ total energy intake for trial (64.3
kcal ± 22.8)
↓ Weekly energy intake (kcal) (varied time
effects), ↔ total energy intake for trial (ND)
↔ Total energy intake (kcal) (ND)
[60]
WP
WP
Healthy subjects (n = 9)
Healthy subjects (n = 5)
↓ Cumulative food intake (weeks 5–9) (varied
time effects)
↔ VAS Hunger (mm) (ND)
↓ Appetite (VAS Haber’s Scale) (2.8 ± 4(?))
WP
Healthy subjects (n = 25)
↓ΔVAS Satiety (mm) (varied time effects)
[44]
WP
Healthy subjects (n = 25)
↔ VAS Hunger (mm) (ND)
[44]
WP
Healthy subjects (n = 16)
↓ Acute energy intake (≈20% ±<20% (SE))
[100]
WP
Healthy subjects (n = 16)
[100]
WP
Healthy M (n = 22)
WP
Healthy M (n = 22)
Oral (liquid test meal) containing 50.8 g
WP
Egg albumin (50.8 g
pro)
WP
Healthy M (n = 22)
Oral (liquid test meal) containing 50.8 g
WP
Tuna (50.8 g pro)
↓ VAS Desire to eat (varied time effects)/
↑Fullness (mm) (varied time effects)
↓ Acute energy intake (563 kJ ± 98.1 (SE)),
↓VAS hunger (62.4 mm ± 16 (SE)) ↓ VAS
prospective food consumption (63.6 mm ±
13 (SE)), ↑ VAS fullness (33.3 mm ± 15 (SE))
↓Acute energy intake (584.7 kJ ± 98.1 (SE)),
↓VAS hunger (79 mm ± 16 (SE)) ↓ VAS
prospective food consumption (82.8 mm ±
13 (SE)), ↑ VAS fullness (40.6 mm ± 15 (SE))
↓ Acute energy intake (325.1 kJ ± 98.1 (SE)),
↓VAS hunger (27 mm ± 16(SE)) ↓ VAS
prospective food consumption (30.4 mm ±
13 (SE)), ↔ VAS fullness (ND)
WP
WP
WP
WP
WP hydrolysate LFD as diet protein source
WP as HFD diet protein source
WP hydrolysate HFD as diet protein source
Additional 24% (wt/wt) of WP (HP-W) or I
flavone-free SP (HP-S)
WP- Oral (beverage) ≈ 10g
WP- Oral, load of WP (8 g) plus
glucomannan (1 g) (0–3 h)
Breakfast custard of WP w/normal protein
(pro/carb/fat = 10/55/35 En%)
Breakfast custard of WP w/high protein
(25/55/20 En%)
Oral, HP liquid preloads (1700 kJ and 48 g
pro)
Oral, HP liquid preloads (1700 kJ and 48 g
pro plus 1.5 g paracetamol)
Oral (liquid test meal) containing 50.8 g
WP
Isocaloric Placebo
Oral, load of CAS (8 g)
plus glucomannan (1g)
Breakfast custard of SP
or CAS
Breakfast custard of SP
or CAS
CAS
CAS
Turkey (50.8 g pro)
[68]
[69]
[97]
[8]
[8]
[8]
[63]
[63]
[41]
[78]
[78]
[78]
[84]
[94]
[92]
[92]
[92]
[62]
[62]
[99]
[47]
[73]
[101]
[101]
[101]
(continued on next page)
14
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
Table 4 (continued )
Treatment
Experimental Model
Dosing
Comparison
Food Intake/Appetite
Reference
WP
Subjects w/overweight (n
= 39)
PPH (300 mL, 1024 kJ,
15 g PPH)
↔ VAS satiety/fullness/desire to eat (mm)
(ND)
[46]
WP
Diabetic M (n = 11)
WP- Oral (beverage/shake), 300 mL, 1024
kJ, % energy from pro/fat/carbs = 25/33/
42 w/150 mL water: WP (15g WP)
WP/WPH- 15 g (68 kcal)
Flavored water (<1
kcal)
[64]
WP
Aged F (n = 10)
WP- 275 kJ
Control (nothing)
WP
Aged F (n = 10)
WP- 275 kJ
EAA Gel- 478 kJ
WP
F w/obesity (n = 8)
WP- 45 g
43 g maltodextrin
↓VAS hunger (122.7 (AUC) ±62.3 (StDe)),
↓VAS prospective food intake (228.3 (AUC)
±68.9 (StDe)), ↑ VAS satiety (172 (AUC)
±46.2 (StDe))
↓composite appetite score (≈24 mm ± 22
mm(StDe))
↓composite appetite score (≈10 mm ± 22
mm (StDe))
↓VAS hunger (≈35% (AUC) ±≈40% (SD)),
↔satiety (mm) (ND)
an EAA gel or nothing (as control) [84]. Moreover, healthy subjects
given a breakfast with varied protein and macronutrient composition
showed WP reduces hunger in a way dependent on meal macronutrient
composition [44]. Rigamonti et al. also showed that WP increased GLP-1
and PYY which was associated with increased satiety and reduced
hunger in females with obesity [82]. Similarly, male with diabetes given
either a whey protein pre-load prior to mixed-nutrient meal challenges
displayed increased fullness and reduced hunger following each meal
challenge [64]. Taken together, leucine consumption may reduce food
intake and/or increase fullness perception. Of the animal studies sum­
marized herein, leucine treatment resulted in reduced hunger in mice or
rats in 7 of 17 studies. Meanwhile, BCAA treatment of mice or rats did
not appear to alter food intake in mice or rats, however protein reduced
food intake in 4 out of 6 mouse or rat studies. In human studies, leucine
was shown to reduce food intake and/or increase fullness in 3 of the 8
studies identified that assessed these outcomes. However, WP con­
sumption more consistently found significantly reduced food intake,
VAS hunger, appetite score and/or desire to eat in 7 of the 12 studies
that assessed WP effects on these indicators. This could suggest BCAA
may provide satiating benefits when consumed in combination with
other amino acids, or that an attribute other than the BCAA may be
responsible for protein’s satiating effects. Please see Table 4 for a sum­
mary of the effects of BCAA on indicators of satiety and food intake.
[84]
[84]
[82]
other mammals (namely rats), as a result of severely reduced BCAA
catabolic capacity in several tissues [7]. Though it is likely both
decreased catabolic capacity and dietary habits contribute to the accu­
mulation of BCAA during disease, it has also been suggested BCAA de
novo biogenesis from the microbiome may further contribute to an
accumulation of BCAA during such diseases [110]. Conversely, low
BCAA abundance has been associated with liver disease and may facil­
itate some resolution [111]. Thus, future studies should also consider
how BCAA consumption/supplementation may affect the various dis­
ease states. With that in mind, future studies should also consider the
potential affect age has on the response of subjects to BCAA, as data
spanning the various life stages is limited. It would also be interesting for
future research to assess the effect of the role of concurrent macronu­
trient consumption with (or without) BCAA, to identify potential in­
teractions among the nutrients, as well as what affect BCAA have on the
consumption of the varied macronutrient. Lastly, additional studies
should also consider by what mechanisms BCAA may act (individually,
as concocted amino acid mixtures, and as complete proteins) as mech­
anistic data are sparse and may be dependent on the experimental
model.
Our article is also not without limitations. First, the studies included
herein are not exhaustive, given the vast literature on BCAA (some of
which was excluded as it is beyond the scope of this summary). How­
ever, a strength of this narrative review is the inclusion of data from
varied models, which allows for a greater insight into potential mech­
anisms of action. Taken together, the data summarized within this report
suggest BCAA may alter satiety, in-part through induction of satiating
hormones (and possibly through other mechanisms, which require
additional investigation).
4. Concluding remarks
In general, evidence concerning the satiating effects of protein
appear to be well-established. However, the individual components
(amino acids) within protein are less studied for their potential effects on
satiety and related hormones. Given the steadily increasing interest in
BCAA, we have summarized much of the current literature of BCAA
either as individual treatment conditions, as a blend, or as a part of a
protein food source (or meal) with comparisons to a similar control
(with reduced BCAA content) on indicators of satiety and food intake. It
appears BCAA may play a causal role in the satiating effects of protein,
however the exact mechanism(s) by which BCAA function remain
somewhat unclear, as is the role of individual versus mixtures of amino
acids or as complete proteins. Thus, future research will need to inves­
tigate if the satiety effects of protein are dependent on the entire
composition of amino acids. Most ideally, future reports will also
consider changes in hormone sensitivity and activity (as these were also
not measured by each report).
Additionally, it is important to mention that BCAA may have po­
tential implications for several diseases [103]. In fact, elevated circu­
lating levels of BCAA correlate with the severity of several metabolic
diseases such as insulin resistance [104–108] and cardiac dysfunction
[109]. In general, elevated circulating BCAA during obesity and/or
diabetes is largely attributed to an inability to degrade BCAA meta­
bolism due to downregulation or inhibition of BCAA catabolic enzymes
(rather than excess dietary intake). In fact, humans (and primates in
general) may be uniquely predisposed to BCAA toxicity compared with
Funding
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-for-profit sectors. All authors
have read and approved the final manuscript. Authors and contributors
declare no conflict of interest.
Author contributions
BL, BCK, MJK, and NPG assisted in the identification and processing
of primary literature, as well as authoring and editing of the final
manuscript. RAV conceived the review, assisted with primary literature
identification and processing, authored the review, and oversaw
manuscript preparation.
Acknowledgments
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-for-profit sectors. All authors
reviewed and authored summaries of the reviewed literature. All au­
thors read and approved the final manuscript. Authors and contributors
15
B. Lueders et al.
Human Nutrition & Metabolism 30 (2022) 200168
declare no conflict of interest.
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