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research-articleXXXX
AJLXXX10.1177/1559827613502444American Journal of Lifestyle MedicineAmerican Journal of Lifestyle Medicine
Jul • Aug 2014
American Journal of Lifestyle Medicine
Analytic
John L. Ivy, PhD, and
Lisa M. Ferguson-Stegall, PhD
Nutrient Timing: The Means to
Improved Exercise Performance,
Recovery, and Training
Adaptation
Abstract: As the incidence rate of
lifestyle-related chronic conditions such
as cardiovascular disease, obesity, and
type 2 diabetes continues to increase,
the importance of regular exercise
and a healthy diet for improving or
maintaining good health is critical.
Exercise training is known to improve
fitness and many health risk factors,
as well as to improve the performance
of competitive athletes. It has become
increasingly clear, however, that
nutrient intake before, during, and
after exercise sessions has a powerful
influence on the adaptive response to
the exercise stimuli. In this review, the
science behind nutrient timing will
be discussed as it relates to exercise
performance, recovery, and training
adaptation. Evidence will be provided
that validates intake of appropriate
nutrients before, during, and
immediately after exercise not only to
improve exercise performance but also
to maximize the training response.
Ultimately, the combined response to
exercise and proper nutrient intake
leads to not only better performance in
athletes but also greater health benefits
for all exercisers.
Keywords: glycogen; endurance;
strength; skeletal muscle; protein
synthesis; body composition
E
xercise training has many
purposes. The average person may
exercise train to maintain or
improve body weight, lower risk factors
associated with disease, or to simply
maintain a healthy lifestyle. For the
athlete, the goal is generally to improve
influence cannot be overstated. Simply
put, without proper nutrition, exercise
goals will not be fully realized.
While proper nutrition is certainly
important in achieving exercise goals, it
has become increasingly evident that
when one eats can be just as important
as what one eats. That is, the timing of
nutrient intervention or “nutrient timing”
can have a significant impact on exercise
performance, recovery, and training
adaptation. These responses to nutrient
Without proper nutrition, exercise
goals will not be fully realized.
athletic performance. While the goals of
the average person and the athlete may
differ substantially, their physiological
and cellular responses to exercise will be
similar as long as exercise intensity and
volume are made relative to fitness level.
However, an important determinant of
the adaptive response to exercise is the
nutritional status of the individual. It has
long been known that diet can have a
major impact on exercise performance as
well as training adaption, and its
timing are not limited to the elite athlete.
Everyone, young and old, male and
female, untrained and trained, will
respond to nutrient timing.
The type of exercise one performs will
dictate the training response of the body.
For example, weightlifting will increase
muscle mass, while endurance cycling
will increase cardiovascular fitness and
muscle endurance. The type of nutrients
consumed and when they are consumed,
however, will substantially affect the
DOI: 10.1177/1559827613502444. Manuscript received March 7, 2013; revised May 10, 2013; accepted March 29, 2013. From the Exercise Physiology and Metabolism
Laboratory, Department of Kinesiology and Health Education, University of Texas at Austin, Austin, Texas (JLI); and the Integrative Physiology Laboratory, Department of
Biology, Hamline University, Saint Paul, Minnesota (LMFS). Address correspondence to John L. Ivy, PhD, Department of Kinesiology and Health Education, University of Texas
at Austin, 1 University Station D3700, Austin, TX 78712; e-mail: johnivy@utexas.edu.
For reprints and permissions queries, please visit SAGE’s Web site at http://www.sagepub.com/journalsPermissions.nav.
Copyright © 2013 The Author(s)
246
vol. 8 • no. 4
quality of an exercise session, rate of
recovery, and magnitude of training
adaptation. In essence, to have quality
exercise sessions, recover fully, and
maximize exercise-training adaptation,
appropriate nutrient supplementation
during and immediately postexercise is
essential. Nutrient supplementation at
critical times of the day and developing a
meal plan that is strategically positioned
around the exercise-training program are
also advantageous.
In this review, the science behind
nutrient timing will be discussed as it
relates to exercise performance, recovery,
and training adaptation. Evidence will be
provided that validates intake of
appropriate nutrients before, during, and
immediately after exercise to improve
exercise performance and maximize the
training response. Nutrient
supplementation and meal planning
throughout the day as it relates to
exercise training will also be discussed.
Nutrient Timing
Simply stated, nutrient timing is the
delivery of appropriate macronutrients
during the time in which the body is
primed to use them most effectively.1
Nutrient timing as it relates to exercise
can be divided into 3 phases: the energy
phase, the anabolic phase, and the
adaptation phase. The energy phase
represents the period immediately prior
to and during exercise. The anabolic
phase is the period immediately after
exercise and lasts for about 60 to 90
minutes. During this time, often referred
to as the anabolic or metabolic window,1
the exercised muscle is highly sensitive
to nutrient intervention. The adaptation
phase follows the anabolic phase, and if
appropriate supplements and meals are
continued during this period an elevated
response to nutrient intervention can be
sustained for many hours, resulting in a
faster recovery and training adaptation.
The Energy Phase
The energy phase is divided into 2
critical time periods: pre-exercise and
during exercise. The pre-exercise period,
which will be discussed first, represents
American Journal of Lifestyle Medicine
Figure 1.
Recommended Nutrient Supplementation During the Energy Phase.
Ingestion of a meal containing 150 to 200 g carbohydrate is recommended 2 to 4 hours preexercise. During prolonged exercise of a moderate to high intensity, ingestion of ~200 mL of a
carbohydrate/protein beverage is recommended. The beverage should contain 2% to 6% carbohydrate + 1% to 2% protein at a ratio of 2:1 carbohydrate/protein for resistance training, or 3-4:1
carbohydrate/protein for endurance training. If exercise intensity is light and the duration is less
than 30 minutes, no supplementation is warranted.
the 4 hours before exercise when
nutrient supplementation can have a
positive influence on exercise
performance. We will then discuss the
primary focus of the energy phase—
nutrient supplementation during
exercise.
The Pre-Exercise Period: 4 Hours or Less
Before Exercise. Dietary strategies such
as carbohydrate loading are designed to
maximize muscle glycogen stores in the
days before an endurance event2 and
have been shown to be effective in not
only increasing glycogen storage to
above-average levels but also to improve
exercise performance in bouts lasting
more than 90 minutes.3-5 However, it has
been demonstrated that ingesting a meal
containing 150 to 200 g of carbohydrate
4 hours before exercise can also
significantly increase muscle glycogen
stores6 and improve exercise
performance.2,7-10
Pre-exercise carbohydrate intake has
not been without controversy, however.
Early research suggested that
carbohydrate consumption 30 to 45
minutes prior to exercise elevated plasma
insulin, resulting in early exercise
hypoglycemia and reduced time to
exhaustion.11 However, the majority of
studies do not support this finding. Most
investigations report either no adverse
effects on performance12-16 or significant
performance improvements2,7-10 following
pre-exercise carbohydrate
supplementation. In addition, some have
demonstrated an additive, positive effect
on performance when supplementation
is provided both before and during
exercise.17,18 Intake of 150 to 200 g
carbohydrate 2 to 4 hours before a long,
intense exercise bout is a reasonable
strategy (Figure 1); however, one should
determine which pre-exercise feeding
strategy works best through experience.
Supplementation During Exercise. Blood
glucose and muscle glycogen are
essential fuel sources during intense,
prolonged exercise, yet the carbohydrate
stores of the body are limited. Skeletal
muscle stores about 300 to 500 g
glycogen, the liver stores 60 to 100 g
glycogen, and only about 15 to 20 g
glucose are available in the blood.19 The
primary purpose of carbohydrate
supplementation during exercise,
especially when prolonged and intense,
is to maintain euglycemia, or normal
blood glucose levels. When blood
glucose becomes low and muscle
glycogen stores are depleted, prolonged
intense exercise simply cannot continue.
Exercise performance. It is well
established that endurance exercise
performance is significantly improved
when carbohydrate is ingested
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Jul • Aug 2014
American Journal of Lifestyle Medicine
during exercise compared to placebo
beverages.20-25 As exercise intensity
increases to ~70% Vo2max or greater,
muscle glycogen is the primary fuel
source.26 As duration increases and
muscle glycogen becomes less available,
metabolism shifts from reliance on
muscle glycogen to blood glucose.20,21
Blood glucose levels have been shown
to decrease to hypoglycemic levels of
~3 mmol L−1 after about 2.5 to 3 hours
of cycling when no supplementation is
provided during exercise, and exercise
cannot continue; however, when
carbohydrate is provided, carbohydrate
oxidation rates can be maintained and
exercise can continue significantly
longer.27 While carbohydrate intake
during exercise maintains blood glucose
levels, it does not appear to spare
muscle glycogen from being used for
fuel during continuous prolonged
exercise at intensities around 70% to
75% Vo2max. Rather, carbohydrate
intake maintains euglycemia and delays
the onset of fatigue.27 However, during
continuous, low-intensity exercise or
variable-intensity exercise, carbohydrate
supplementation has been found
to improve endurance performance
by sparing muscle glycogen.24,25,28
Supplementation does not have to
start at the onset of exercise to be
effective. It has been shown that starting
supplementation before a significant
decline in blood glucose occurs can still
prolong aerobic endurance.20
Carbohydrate supplementation has also
been found to benefit resistance exercise.
Wax et al provided 1 g carbohydrate per
kg body mass immediately before and
0.17 g carbohydrate per kg body mass
every 6 minutes during an isometric
resistance exercise protocol to fatigue
and found that total force output was
higher when carbohydrate was provided
compared with placebo.29 Likewise, Haff
et al found that carbohydrate
supplementation increased the total
amount of work that could be performed
during an isokinetic resistance exercise
session consisting of 16 sets of 10
repetitions at 120° s−1 consisting of knee
extension and flexion.30 Therefore,
carbohydrate intake can benefit
248
resistance exercise performance, as well
as endurance performance.
Effect of multiple carbohydrate types
on endurance performance. Several
investigations have demonstrated that
when multiple carbohydrate types (eg,
dextrose, fructose, and maltodextrin) are
ingested, the maximal rate of exogenous
carbohydrate oxidation can be increased
significantly.31-33 Recent investigations
have demonstrated that endurance
performance can be improved as well.
Currell and Jeukendrup reported an
8% improvement in time to complete
a simulated time trial when cyclists
ingested a glucose–fructose (2:1 ratio)
supplement compared to isocaloric
glucose only supplement provided
immediately before and every 15
minutes during exercise.34 Others have
shown significant improvements in time
to exhaustion when supplementing
with a combination of dextrose,
maltodextrin, and fructose with added
whey, compared to dextrose only.35
It is believed that ingesting multiple
carbohydrates optimizes the use
of various intestinal carbohydrate
transporters such that the rate of
absorption is increased beyond that
of a single carbohydrate and leads to
increased exogenous carbohydrate
oxidation, which spares endogenous
carbohydrate stores.31
Effect of Carbohydrate Supplementation
on Immune System Function. While
moderate to vigorous endurance exercise
is associated with bolstered immune
system function, prolonged and
exhaustive exercise can negatively
impact the immune system, resulting in
decreased immune function and higher
rates of upper respiratory tract
infections.36-39 Many nutritional
countermeasures have been investigated
for immune system protection, including
glutamine, bovine colostrum,
carbohydrate beverages, phytonutrients
such as quercetin, and antioxidants such
as vitamins C and E.40-44 Of these,
carbohydrate ingestion has been
demonstrated to be the most
effective.37,40
Carbohydrate ingestion can attenuate
exercise-induced changes in plasma
cortisol and epinephrine, which can
suppress immune function during and
after prolonged endurance events such
as marathons.45,46 Compared to runners
ingesting a placebo treatment, those who
ingested carbohydrate during exercise
had significantly lower plasma cortisol
levels and decreased leukocyte
trafficking.37,45 Similar results have been
shown in exhaustive, prolonged cycling.
Scharhag et al provided placebo, 6%, or
12% carbohydrate beverages during 4
hours of cycling and reported that the
ingestion of 6% carbohydrate
significantly attenuated the exerciseinduced immune response, of phagocytic
neutrophils and monocytes via a
reduction in cortisol release. Moreover,
increasing the concentration to 12%
carbohydrate provided no additional
improvement in immune function over
that of the 6% beverage.47
Others have demonstrated that
ingesting carbohydrate compared to
placebo during prolonged endurance
cycling or running attenuates the
increase in both pro- and antiinflammatory cytokines, which are
potent mediators of the immune system
and the inflammatory response.40,46,48-51
Taken together, these results strongly
indicate that carbohydrate intake can
have a significant positive effect in
attenuating suppressed immune function
and the inflammatory cascade during
and after intense, prolonged exercise.
Carbohydrate/Protein Supplementation
During Exercise. Several investigations
have reported significant improvements
in endurance exercise performance when
a carbohydrate/protein beverage is
ingested during exercise compared to a
carbohydrate-only beverage.35,52-56 Ivy et
al compared the effects of placebo,
carbohydrate only, and carbohydrate/
protein supplementation on endurance
performance in trained cyclists. The
participants cycled at intensities
alternating between 45% and 75%
Vo2max for 3 hours, and then at 74% to
85% Vo2max until exhausted.
Supplements (200 mL) were provided
vol. 8 • no. 4
every 20 minutes during exercise. While
carbohydrate supplementation
significantly increased time to
exhaustion, the carbohydrate/protein
supplementation extended time to
exhaustion by 36.5%.52 Saunders et al
reported similar time to exhaustion
improvements with carbohydrate/protein
compared to carbohydrate
supplementation during exercise. Fifteen
cyclists exercised at 75% Vo2max to
exhaustion, followed 12 to 15 hours later
by a second ride to exhaustion at 85%
Vo2max. Participants received
supplements every 15 minutes of
exercise and immediately postexercise.
The cyclists rode 29% longer in the first
and 40% longer in the second ride when
consuming carbohydrate/protein
compared to the carbohydrate
beverage.54 Saunders and colleagues also
demonstrated a 13% improvement in
time to exhaustion when a carbohydrate/
protein gel was compared to a
carbohydrate-only gel ingested every 15
minutes during a cycling bout to
exhaustion.55 It should be noted that in
some of the above-referenced studies,
the supplements provided were not
isocaloric but rather
isocarbohydrate.52,54-56 However, other
investigations using a carbohydrate/
protein supplement that contained fewer
calories compared to a carbohydrate
supplement demonstrated significant
performance improvements.35,53 These
collective findings demonstrate the
potential for improved time to
exhaustion when carbohydrate and
protein are co-ingested during endurance
exercise.
As discussed earlier, a mixture of
carbohydrate types has been shown to
be more effective than a single type in
improving performance. Given that
adding protein to a carbohydrate
supplement can improve endurance
performance compared to carbohydrate
only, recent studies investigated the
combined effects of multiple
carbohydrate types plus added whey
protein on endurance performance.
Ferguson-Stegall et al compared the
effects of a 6% carbohydrate beverage or
a 3% carbohydrate/1.2% protein
American Journal of Lifestyle Medicine
beverage on time to exhaustion during
cycling exercise.35 The carbohydrate
beverage contained 6% dextrose, and the
carbohydrate/protein beverage contained
1% each of dextrose, maltodextrin, and
fructose, and 1.2% whey protein isolate.
Supplementation was provided every 20
minutes during exercise. Time to
exhaustion was 28.7% greater in the low
carbohydrate/protein treatment
compared to the carbohydrate treatment
when exercise intensity was near
ventilatory threshold.35 McCleave and
colleagues also found significantly
improved time to exhaustion in trained
female cyclists and triathletes when
comparing a mixed carbohydrate/
moderate protein supplement with a
higher calorie carbohydrate
supplement.53 These results suggest that
the efficacy of a supplement in
benefitting endurance performance can
be optimized by using multiple
carbohydrate types and adding a
moderate amount of protein. This may
be of particular interest to athletes and
exercisers who desire a lower-calorie
alternative when exercising to meet
weight loss or body composition goals.
While the benefits of carbohydrate/
protein supplementation have been
demonstrated during endurance exercise,
a recent investigation found improved
performance in simulated soccer-type
exercise.57 Using the Loughborough
Intermittent Shuttle Test, which includes
jogging, running, and sprinting,58
Highton and colleagues demonstrated a
trend for improved distance covered and
sustained speed when participants
ingested at 15 minutes intervals during
exercise a beverage containing 6%
carbohydrate and 2% whey protein
compared to 8% carbohydrate only.57
Moreover, carbohydrate/protein
supplementation has been shown to
attenuate muscle damage during
resistance exercise.59 Therefore, the
benefits of carbohydrate/protein
supplementation extend beyond
endurance exercise and have relevance
to sport-specific performance and
resistance exercise training as well.
Despite the many reports of improved
endurance and sport performance with
carbohydrate/protein, some studies using
isocaloric carbohydrate and
carbohydrate/protein treatments found
no difference in time to exhaustion60-62 or
in time trial performance.63 Given the
conflicting findings across studies, and
the relatively small sample sizes used in
many of the investigations, Saunders et al
examined data across multiple studies to
determine if performance was in fact
related to changes in physiological
measures during exercise.64 To
accomplish this, 38 subjects were
combined from 3 studies in which
cyclists performed rides to exhaustion at
75% Vo2peak. In each study analyzed,
cyclists received carbohydrate (7.3%) or
carbohydrate/protein (7.3% + 1.8%)
every 15 minutes during exercise.
Despite finding no differences in oxygen
consumption, blood glucose, or
respiratory exchange ratio between
carbohydrate and carbohydrate/protein
treatments, time to exhaustion was 19%
longer during the carbohydrate/protein
treatment compared to the carbohydrate
treatment across studies. Thus, the
authors concluded that the combined
data showed significant improvements in
endurance performance with
carbohydrate/protein versus
carbohydrate supplementation.64
Effect on Carbohydrate/Protein
Supplementation on Muscle Damage and
Soreness. In 2 investigations previously
described by Saunders and colleagues,
carbohydrate/protein supplements
ingested during endurance exercise
resulted in longer times to exhaustion
compared to carbohydrate alone, and
also demonstrated lower levels of plasma
creatine kinase (CPK) in the
carbohydrate/protein treatment
compared to carbohydrate only.54,55
Saunders et al also compared the effects
of a 6% carbohydrate beverage with a
6% carbohydrate/1.8% protein
hydrosylate beverage taken during and
immediately after a 60 km simulated time
trial on plasma CPK levels as well as
muscle soreness ratings 24 hours
postexercise.56 Plasma CPK and ratings
of muscle soreness were significantly
increased compared to pre-exercise
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Jul • Aug 2014
American Journal of Lifestyle Medicine
levels in the carbohydrate only treatment,
but no significant increases were found
when the combination beverage was
ingested.56
While the early research of Saunders
and colleagues54-56 suggested that the
addition of protein was in some way
protective against muscle damage and
soreness 24 hours postexercise, it was
not evident if this effect was due to the
protein itself or the additional energy
provided in the nonisocaloric beverage.
To address this question, Valentine et al
investigated the effects of carbohydrate
and carbohydrate/protein beverages
matched for both carbohydrate and
caloric content on plasma CPK and
myoglobin.62 Participants ingested 250
mL of placebo, carbohydrate (7.75%),
carbohydrate plus carbohydrate (9.69%),
and carbohydrate/protein (7.75%
carbohydrate and 1.94% protein) every
15 minutes during cycling exercise at
75% Vo2max to exhaustion. Time to
exhaustion did not differ between the 2
isocaloric, higher calorie treatments;
however, plasma CPK and myoglobin
were lower in the carbohydrate/protein
treatment, and leg strength, assessed 24
hours postexercise, was higher in the
carbohydrate/protein treatment. This
suggests that improvements in
postexercise muscle damage occurs
independent of caloric content and is
likely related to the addition of protein.62
Summary of the Energy
Phase. Carbohydrate is an essential fuel
source for exercise, and ingesting
carbohydrate before as well as during
endurance exercise can improve exercise
performance, delay the onset of fatigue,
and protect immune system function. A
supplement containing a mixture of
carbohydrate sources can increase time
to exhaustion compared to ingestion of a
single carbohydrate source, presumably
by sparing endogenous carbohydrate
stores. The addition of protein to a
carbohydrate supplement has been
found to reduce muscle damage that
occurs after intense endurance as well as
resistance exercise. It also may improve
exercise performance beyond that of
carbohydrate alone, although this has not
250
been a universal finding. The benefits of
supplementation are relevant for both
endurance exercise and resistance
training and apply to both recreational
exercisers and elite athletes. A practical
strategy for supplementation during
exercise is to ingest a beverage
containing 3.0% to 6.0% carbohydrate
every 15 to 20 minutes during prolonged
exercise (Figure 1). One should also
consider the addition of 1.0% to 1.5%
protein to their supplement.
The Anabolic Phase
It has often been said that breakfast is
the most important meal of the day, and
recent research appears to support this
claim. However, a claim can be made
that the second most important meal of
the day is the postexercise supplement.
Immediately after an intense exercise
training session the body is in a
catabolic state. Blood insulin is low,
cortisol and other catabolic hormones
are elevated, muscle and liver glycogen
levels are reduced or depleted, muscle
protein breakdown is elevated, and
substrate availability is low. Once
exercise has ceased, this catabolic state
will prevail for many hours unless
actions are taken to shift the body into a
predominately anabolic state. To make
this metabolic shift, nutrient intervention
is required.
The exercised skeletal muscle is very
responsive to nutrient intervention
postexercise. When carbohydrate and
protein are ingested in the minutes
post-exercise, the glucose and amino
acids derived from these macronutrients
initiate the shift to an anabolic state by
raising blood insulin levels, lowering
cortisol and other catabolic hormones,
and increasing substrate availability.
Because muscle is highly insulin sensitive
postexercise, this ensures the rapid
uptake of blood glucose and amino
acids, which promotes muscle glycogen
and protein synthesis, while also
reducing protein breakdown. Since
insulin sensitivity declines with time, the
effectiveness of nutrient intervention will
also decline. Consuming the appropriate
types and amounts of nutrients
immediately to 45 minutes after an acute
bout of exercise can increase the rate of
muscle glycogen storage, reduce muscle
damage, increase protein accretion, and
speed exercise recovery. When
incorporated into an exercise-training
program, this results in greater training
adaptation.
Muscle Glycogen Storage. Although
muscle glycogen represents less than 4%
of the total energy stores in the body, it
is the most important fuel source during
prolonged moderate-to-high exercise,
high-intensity interval exercise, and
resistance exercise. Moreover, research
suggests that the activity of a number of
metabolic enzymes including those
controlling glucose transport and protein
metabolism is influenced by the
glycogen level of the muscle. For these
reasons, the restoration of muscle
glycogen is paramount in the exercise
recovery process.
Timing of carbohydrate
supplementation. Postexercise muscle
glycogen synthesis occurs more rapidly
when carbohydrate is consumed
immediately after exercise as opposed
to waiting several hours.65 Muscle
glycogen synthesis rates range between
5 and 7 µmol g−1 wet wt h−1 over 4
hours of recovery when carbohydrate
is consumed immediately postexercise,
and these rates can be maintained for 6
to 8 hours by continuing carbohydrate
supplementation at 2-hour intervals.65-67
Moreover, synthesis rates have been
reported to be in excess of 15 µmol
g−1 wet wt h−1 during the first 30 to 40
minutes after exercise.68,69 Delaying
supplementation for 2 hours reduces
the rates of muscle glucose uptake and
glycogen synthesis by 50% or more
and occurs despite normal increases in
blood glucose and insulin levels.65,70 If
carbohydrate is not adequately supplied
postexercise, the rate of muscle glycogen
synthesis can be extremely low.66
Therefore, providing a carbohydrate
supplement soon after exercise has the
added benefit of starting the muscle
glycogen recovery process immediately,
thereby maximizing the effective
recovery time.
vol. 8 • no. 4
The frequency and amount of
carbohydrate supplementation can have
dramatic effects on the rate of glycogen
storage. Ivy et al found that
supplementing at 2-hour intervals with
1.2 to 1.5 g glucose kg−1 body mass
increased the glycogen synthesis rate up
to 5 to 7 µmol g−1 wet wt h−1.66 When
supplements exceeded 1.5 g glucose kg−1
body mass, the synthesis rate did not
increase further. However, research
suggests that faster rates of synthesis can
be obtained during the immediate hours
postexercise with greater amounts of
carbohydrate if frequency of
supplementation is also increased.71-74
For example, Jentjens et al72 and van
Loon et al74 reported synthesis rates of 8
to 10 µmol g−1 wet wt h−1 when subjects
were provided 1.2 g glucose kg−1 body
mass h−1 at 30-minute intervals over 3 to
5 hours of recovery. Increasing the
amount of carbohydrate ingested to 1.6 g
kg−1 body mass h−1, however, did not
have an additional benefit.75 While
muscle glycogen synthesis can be
maximized with carbohydrate intake of
approximately 1.2 g kg−1 body mass h−1
provided in 15- to 30-minute increments,
this amount of carbohydrate is excessive
and the frequency of supplementation
impractical.
Addition of protein to a carbohydrate
supplement. Many investigators have
demonstrated that the addition of protein
to a carbohydrate supplement can
significantly enhance the rate of muscle
glycogen synthesis during the first 4
hours of recovery.69,76-79 However, not
all studies support these findings.72-75
The differences in findings can most
likely be attributed to differences in
experimental design, including frequency
of supplementation, and the amount
and type of carbohydrate and protein
provided. The evidence, however,
is considerable that the addition of
protein to a carbohydrate supplement
will increase the efficiency of muscle
glycogen storage when the amount
of carbohydrate ingested is below the
threshold for maximal glycogen synthesis
or when feeding intervals are 1 hour
or more apart.69,76-79 In fact, maximum
American Journal of Lifestyle Medicine
rates of muscle glycogen synthesis
can be achieved with substantially less
carbohydrate and reduced frequency
of supplementation when protein
and carbohydrate are coingested.
Furthermore, a carbohydrate/protein
supplement has the added benefits of
reducing muscle damage and soreness
and increasing protein synthesis.
Muscle Damage and Soreness. Muscle
damage during exercise occurs from the
mechanical stress placed on the muscle
fibers and the catabolic hormonal
environment that increases muscle
protein breakdown postexercise.80 The
longer nutrient supplementation is
delayed postexercise, the longer this
catabolic state prevails, leading to
increased muscle damage, inflammation,
and soreness.
Acute supplementation. Roy et al
found that consuming a carbohydrate
supplement (1 g kg−1 body mass)
immediately after resistance exercise
reduced 3-methylhistidine excretion and
urea nitrogen during the first 10 hours
of recovery.81 These results suggest that
adequate carbohydrate supplementation
can decrease myofibrillar protein
breakdown and limit muscle damage.
Etheridge et al reported that consuming
100 g of protein immediately after 30
minutes of downhill running prevented
a decline in maximal quadriceps
strength and power output during a
72-hour recovery period. However, the
supplement had no effect on limiting
the increase in blood markers of
muscle damage or ratings of muscle
soreness.82 Cockburn et al compared
the effects of water, a carbohydrate
sports drink, milk, and a milk-based
carbohydrate/protein supplement on
muscle soreness, isokinetic muscle
performance, and plasma CPK and
myoglobin concentrations. At 48 hours
postexercise, milk and milk-based
carbohydrate/protein supplementation
had attenuated the decrease in isokinetic
muscle performance and increases in
CPK and myoglobin relative to water
and the carbohydrate sports drink.83 In
a subsequent study, these researchers
found that consuming the milk-based
carbohydrate/protein supplement
postexercise as compared to preexercise limited development of muscle
soreness and better maintained muscle
strength over 48 hours of recovery.84
However, White et al reported that
supplementing with carbohydrate/
protein before or after eccentric
quadriceps contractions on an isokinetic
dynamometer had no effect on muscle
damage, soreness, or performance
up to 96 hours postexercise.85 Also,
Wojcik and colleagues reported that
eccentric exercise increased muscle
protein breakdown as indicated by
urinary 3-methylhistidine levels and
increased plasma IL-6 with no effect of
carbohydrate or carbohydrate/protein
supplementation. Quadriceps isokinetic
peak torque was depressed similarly for
all groups 24 and 72 hours postexercise
as well.86 Of course, the differences in
findings may be accounted for by the
type of exercise used to induce muscle
damage, the degree of muscle damage
imposed, the type of supplement
provided, and the lack of controlling
participants’ dietary intake outside of the
experimental trials.
Chronic supplementation. The
benefits of carbohydrate/protein
supplement over subsequent days of
training have also been investigated.
Luden et al provided a carbohydrate or
carbohydrate/protein beverage to 23
runners immediately after each training
session for 6 days before a crosscountry race. After a 21-day washout
period, subjects repeated the protocol
with the alternate beverage. Although
postintervention CPK and soreness were
significantly lower after carbohydrate/
protein supplementation than after
carbohydrate supplementation, running
performance did not differ between
treatments. However, it was noted that
the runners with the highest training
mileage had the most improvement in
race performance after the carbohydrate/
protein supplement.87 Chronic
carbohydrate/protein supplementation
of US Marine recruits was found to be of
benefit to their health during 54 days of
251
Jul • Aug 2014
American Journal of Lifestyle Medicine
basic training.88 Recruits were randomly
assigned to placebo, carbohydrate,
or carbohydrate/protein treatment
groups. Compared with placebo and
carbohydrate groups, the carbohydrate/
protein supplementation group had
an average of 33% fewer total medical
visits, 28% fewer visits due to bacterial/
viral infections, 37% fewer visits due to
muscle/joint problems, and 83% fewer
visits due to heat exhaustion. Muscle
soreness immediately postexercise
was reduced by carbohydrate/protein
supplementation compared with placebo
and carbohydrate groups on both days
34 and 54.88
In summary, postexercise carbohydrate/
protein supplementation may be more
effective than carbohydrate only in
reducing indicators of muscle damage
and soreness. This may be especially
significant during periods of intense,
chronic exercise training.
Effect on Protein Accretion. Protein
accretion is determined by the difference
in protein synthesis and degradation.
Following an acute bout of exercise,
protein synthesis increases; however, net
protein balance is negative as the
increase in protein synthesis is offset by
increased protein breakdown.89 Ingestion
of amino acids or protein postexercise,
however, stimulates protein synthesis,
resulting in a positive net protein
balance.90,91
Acute effect. The first study to
demonstrate the importance of nutrient
timing on muscle protein synthesis was
conducted by Okamura and colleagues.92
Dogs were exercised by treadmill
running and infused with a glucose/
amino acid mixture immediately or 2
hours postexercise. When the dogs were
infused immediately postexercise, muscle
protein synthesis increased significantly
within 15 minutes. When infusion of the
mixture was delayed for 2 hours, there
was no increase in protein synthesis;
furthermore, when the infusion was
started after the 2-hour delay, the
synthesis rate was significantly lower
than observed when infusion occurred
immediately postexercise. It was
252
concluded that stimulation of protein
accretion is better served by provision
of nutrients sooner rather than later
postexercise.92 This view was supported
by the research of Levenhagen et al.70
Cyclists were provided a carbohydrate/
protein supplement immediately or 3
hours after cycling at moderate intensity
for 1 hour. Whole body and muscle
protein synthesis were determined
during the 3 hours after supplementation.
When the supplement was provided
immediately postexercise, whole body
protein synthesis was 12% higher and
leg muscle protein synthesis 300% higher
than when the supplement was delayed.
Importantly, positive protein balance
was only reached when supplementation
occurred immediately post-exercise.70
Whether there is an advantage to
nutritional supplementation within the
first hour after exercise has been recently
challenged.93 It has been pointed out
that the rate of protein synthesis was the
same when a supplement composed of 6
g of an essential amino acid (EAA)
mixture and 36 g of carbohydrate was
provided either 1 or 3 hours after
resistance exercise.94 It was also reported
by Tipton et al that immediate preexercise ingestion of an EAA/
carbohydrate solution resulted in a
significantly greater and more sustained
muscle protein synthesis response
compared to its immediate postexercise
ingestion.95 Moreover, the effect of an
acute bout of exercise on muscle protein
synthesis has been found to last for
several days.96,97
A closer evaluation of these studies,
however, shows they do not refute or
diminish the importance of
supplementation in the first hour
postexercise. First, Fujita et al found that
supplementing 1 hour before exercise
with an EAA/carbohydrate supplement
did not result in enhanced postexercise
muscle protein synthesis.98 Second,
Tipton et al later reported no significant
difference in net muscle protein
synthesis postexercise when 20 g of
whey was consumed immediately before
versus 1 hour postexercise.99 Third, when
the effect of timing of nutrient
supplementation on protein synthesis
postexercise is evaluated, the supplement
ingested closest in time to the exercise
generally has the greatest impact. For
example, the increases in muscle protein
synthesis reported by Phillips et al at 3,
24, and 48 hours after exercise were
112%, 65%, and 34%, respectively.97
Finally, there are few studies that actually
compare the response of
supplementation immediately or within
the first 45 minutes postexercise with
delaying supplementation for several
hours as evaluated by Okamura et al92
and Levenhagen et al.70 In summary,
most acute exercise studies clearly
support supplementation soon after
exercise for optimal stimulation of
protein synthesis and protein accretion.
Chronic effect. Results from a
number of exercise training studies using
various forms of exercise and subject
populations support the use of early
postexercise nutrient intervention to
enhance training adaptation. Suzuki et
al investigated the effect of meal timing
after exercise on body composition in 20
male rats assigned to groups fed either
immediately or 4 hours postexercise.
Resistance exercise (squatting) was
conducted 3 days per week for 10
weeks. At the completion of training,
body weight was comparable between
the groups. However, hind limb muscle
weight was 6% higher and adipose tissue
weight 24% lower in rats fed immediately
after exercise compared with rats fed 4
hours postexercise.100 One of the first
human studies addressing the effect of
nutrient timing on training adaptation
corroborated these results in elderly
men.101 Esmarck et al investigated
the effects of nutrient timing in 13
men (74 ± 1 years) who completed a
12-week resistance-training program
while receiving a carbohydrate/protein
supplement immediately after or 2 hours
after each exercise session. Subjects
receiving the supplement immediately
postexercise had a significant increase
in fat-free mass, cross-sectional
area of the quadriceps femoris, and
mean muscle fiber area, whereas no
significant increases in these parameters
were observed for subjects receiving
vol. 8 • no. 4
supplementation 2 hours postexercise.
Increases in dynamic and isokinetic
muscle strength were also greater in
subjects supplemented immediately
postexercise.101
Cribb and Hayes demonstrated the
efficacy of nutrient timing in young
resistance-trained men. Their exercise
program consisted of 12 weeks of
resistance training before
supplementation started, followed by 10
more weeks of resistance training after
onset of supplementation. The
supplement consisted of a mixture of
carbohydrate, protein, and creatine and
was provided immediately before and
after exercise in one group and before
breakfast and late evening before sleep
in a second group. At the completion of
training, the subjects that received the
supplement pre- and postexercise had a
100% greater increase in lean body mass
and a 33% greater increase in the
cross-sectional area of the IIa and IIx
muscle fibers from the vastus lateralis
than subjects receiving the supplement at
the beginning and end of the day.
Furthermore, improvements in strength
were significantly greater in subjects
supplemented immediately pre- and
postexercise.102 Similar results were
found by Hulmi et al.103 These
investigators provided protein (15 g of
whey) or nonenergetic placebo to
subjects immediately before and after
each resistance exercise session. Exercise
sessions were performed twice per week
over 21 weeks. Protein supplementation
increased muscle cross-sectional area
and altered muscle mRNA expression in
a manner advantageous for muscle
hypertrophy.103
Supplementation during exercise has
also been found to improve training
adaptation to resistance exercise. Bird et
al conducted a 12-week resistance
exercise-training program in which
supplementation (6% carbohydrate, 6 g
EAA, 6% carbohydrate + 6 g EAA, or
placebo) was provided throughout each
exercise session.104 Bird et al reported
the carbohydrate/EAA supplementation
increased lean body mass and the
cross-sectional areas of type I, IIa, and
IIb muscle fibers compared with placebo
American Journal of Lifestyle Medicine
and reduced myofibrillar protein
breakdown as indicated by a reduced
urinary excretion of 3-methylhistidine 48
hours after the last exercise session.
Interestingly, the provision of
carbohydrate and EAA separately
improved body composition and muscle
fiber cross-sectional area relative to
placebo, but these improvements were
not as advantageous as those seen with
the carbohydrate/EAA supplement.104
These results support the additive effect
of carbohydrate and protein
supplementation on protein accretion.
Only a few studies have investigated
the effects of nutrient timing on
adaptation to aerobic exercise training.
Ferguson-Stegall et al compared the
effects of a carbohydrate/protein
supplement (low-fat chocolate milk),
isocaloric carbohydrate supplement, and
a calorie-free placebo on training
adaptation occurring over 4.5 weeks of
exercise training.105 Subjects cycled 60
min d−1, 5 d−1 wk−1 at 75% to 85% of
Vo2max. Supplements were ingested
immediately and 1 hour after each
exercise session. No supplementation
was allowed for 1 hour after the final
supplement was provided. Vo2max was
improved by 12.5% with carbohydrate/
protein supplementation, and this
improvement was twice as great as
occurred when consuming carbohydrate
only or placebo.105 Okazaki and
colleagues also found that carbohydrate/
protein supplementation provided
immediately after daily cycling exercise
in older male subjects increased Vo2max
compared to a placebo.106 Vo2max
increased 3.3% with placebo
supplementation and 6.8% with
carbohydrate/protein supplementation.
Significant increases in stroke volume
and plasma volume only occurred
following carbohydrate/protein
supplementation.106 Taken together, these
findings suggest a faster rate and
magnitude of training adaptation when
carbohydrate and protein are coingested
after endurance exercise.
Ferguson-Stegall et al also reported that
carbohydrate/protein supplementation in
the form of low-fat chocolate milk
resulted in greater improvements in body
composition.105 This result is supportive
of the findings of Josse and colleagues,
who studied the effects of daily exercise
and a hypoenergetic diet varying in
protein and calcium content from dairy
foods on the composition of weight lost
over 16 weeks in premenopausal,
overweight, and obese women.107
Participants were randomly assigned to a
high protein, high dairy (HPHD; total
protein, 1.33 ± 0.04 g/kg d−1), adequate
protein, medium dairy (APMD; total
protein, 0.84 ± 0.02 g/kg d−1), or
adequate protein, low dairy (APLD; total
protein, 0.72 ± 0.02 g/kg d−1) treatment
group. The quantity of total dietary
protein and dairy food-source protein
was 30% and 15%, 15% and 7.5%, and
15% and less than 2% for the HPHD,
APMD, and APLD groups, respectively.
Dairy protein consumption for each
group was controlled by the number of
supplements per day. Weight loss was
the same for all groups; however, fat loss
during the last 8 weeks of treatment was
greater in the HPHD group than in the
APMD and APLD groups. Also, the
HPHD group demonstrated a significant
gain in lean mass, whereas the APLD and
APMD groups lost lean mass. These
findings highlight the importance of
protein supplementation in exercise
programs designed for weight
management.
Not all studies have found that nutrient
supplementation postexercise results in a
faster training adaptation. Verdijk et al
trained 2 groups of elderly men (72 ± 2
y) for 3 d wk−1 for 12 weeks.108 One
group ingested 10 g of protein before
and immediately after each exercise
session, and the other group received a
placebo. All training occurred 90 minutes
after a standardized breakfast. Leg
strength and quadriceps mass increased
significantly with no difference between
groups. The investigators concluded that
protein supplementation immediately
before and after exercise does not further
augment the increase in skeletal muscle
mass and strength after prolonged
resistance-type exercise training in
healthy elderly men when their daily
protein consumption is normal.108 While
a well-controlled study, it has notable
253
Jul • Aug 2014
American Journal of Lifestyle Medicine
limitations. The amount of protein
provided was rather small, as it has been
reported that a much higher amount of
protein is required to maximize
postexercise protein synthesis in elderly
men.109-111 The exercise sessions were
also carried out only 90 minutes after
breakfast. It is highly likely that nutrients
from breakfast were still being
metabolized during and following the
exercise sessions in both the placebo
and protein groups and therefore
prevented a true evaluation of effects of
protein supplement ingestion
immediately before and after exercise on
the adaptive response.
Hoffman et al112 and Erskine et al113
also found no improvement in training
adaptation when supplementing with
protein around each exercise session.
Hoffman et al studied the effect of 10
weeks of protein supplement timing on
strength, power, and body composition
in resistance-trained men.112 Erskine et al
evaluated the effect of protein
supplementation over 12 weeks of elbow
flexor resistance exercise. Participants
were randomly assigned to receive
protein or placebo before and after each
exercise session.113 However, in neither
the Hoffman et al112 nor Erskine et al113
studies was nutrient consumption
controlled after the exercise training
sessions. In summary, most investigations
demonstrate that supplementation that
ensures appropriate nutrient levels within
the first 45 minutes postexercise results
in the greatest adaptive response to
endurance as well as resistance exercise
training.
Appropriate postexercise nutrient
supplement. Both amino acid and
protein supplementation postexercise
stimulates protein synthesis. However,
the type and amount of these nutrients
affects the magnitude of response.
Several studies have reported that only
the EAA are necessary for stimulation of
muscle protein synthesis.114,115 Of these,
leucine appears to be of most importance
because of its ability to activate the
mTOR signaling pathway, which controls
mRNA translation.116 Whey protein, which
comprises about 20% of milk protein,
254
Figure 2.
The relative Increase and Duration
in Muscle Protein Synthesis
(MPS) Following Postexercise
Supplementation With Different
Proteins or Protein Mixtures.
Milk protein is approximately 20% whey
and 80% casein. The protein blend was
50% protein from sodium caseinate, 25%
protein from whey isolate, and 25% protein
from soy isolate.11 Results from References
117, 118, and 119 were used to generate
Figure 2.
has a high leucine content and is rapidly
digested. Milk protein has been found to
promote greater muscle protein accretion
than soy protein after exercise.117
Moreover, isolated whey protein was
found to stimulate muscle protein
synthesis to a greater degree than casein
and soy protein.118 There are few studies
comparing protein mixtures. However,
Riedy et al recently reported that a blend
of whey and soy protein prolonged the
elevation in blood amino acid levels
after ingestion relative to whey protein
alone and produced a greater total
muscle protein synthesis.119 However,
simply maintaining an elevated blood
amino acid profile does not guarantee
that protein synthesis will continue,120,121
suggesting that more research needs
to be conducted to determine if
combinations of fast and slow digesting
proteins will have an overall greater
effect on protein synthesis and accretion
(Figure 2).
Carbohydrate ingestion has also been
found to stimulate protein synthesis
postexercise, most likely as a result of
increased insulin secretion.81,122,123 Insulin
is also a strong inhibitor of muscle
protein breakdown,91 and many studies
suggest that the combination of
carbohydrate and either protein or EAA
can have an additive effect on muscle
protein synthesis and net whole body
protein balance.75,123,124 Chronic training
studies comparing carbohydrate plus
protein or EAA supplementation with
protein supplementation alone also
support the superiority of a combination
of macronutrients to stimulate recovery
and training adaptation.104-106 The
amount of supplementation is also of
importance. Cuthbertson and colleagues
have estimated that consuming 10 g of a
mixture of EAA could maximize muscle
protein synthesis,125 and Moore et al
reported that 20 g of whey protein
provided soon after resistance exercise
maximized muscle protein synthesis in
young adults.126 However, for older
individuals, the requirement may be as
high as 40 g.109-111 These results have
been used to make recommendations
regarding postexercise protein
supplementation. However, the rate of
protein accretion is also affected by the
rate of protein breakdown. Recently,
Deutz and Wolfe provided strong
evidence that with increased
carbohydrate/protein intake, there is a
progressively greater insulin response,
resulting in a proportional inhibition of
muscle protein breakdown and increased
protein accretion.127 If true, this suggests
that there is no practical upper limit to
the anabolic response to protein when
combined with carbohydrate in a
supplement or in the context of a meal.
The Adaptation Phase
The adaptation phase represents the 4
to 6 hours after the effects of the initial
postexercise supplement have dissipated.
As described earlier, a rapid rate of
muscle glycogen storage that follows
postexercise supplementation can be
maintained up to 6 to 8 hours with
periodic carbohydrate feedings.65-67 A
similar pattern is likely to occur with
protein synthesis. Phillips et al found that
supplementing with a carbohydrate/
protein supplement 24 and 48 hours
vol. 8 • no. 4
after exercise resulted in an increase in
muscle protein synthesis, although the
response was not as high as when
supplementing 3 hours postexercise.97
Continuously maintaining high blood
amino acid levels, however, does not
mean that protein synthesis will be
sustained as protein synthesis is only
elevated for about 1 to 2 hours following
carbohydrate/amino acid
supplementation.94,128 Likewise, raising
blood amino acid levels to 1.7-fold above
basal level via intravenous infusion
increases muscle protein synthesis within
0.5 hours of infusion onset; however,
despite maintaining elevated blood
amino acid levels with continuous
infusion the rate of muscle protein
synthesis declines to near baseline level
within 2 hours.121
Recently, West et al provided whey
protein either as a single 25-g bolus or as
repeated, small, “pulsed” 2.5-g protein
drinks every 20 minutes for 200 minutes
in a nonexercised state and after
resistance exercise.129 Providing the
protein as a bolus increased blood EAA
levels above those when pulsing the
supplementation the first 60 minutes
postexercise. Pulsed supplementation
resulted in a smaller but sustained
increase in aminoacidemia that remained
elevated above that produced by the
bolus supplement from 180 to 220
minutes after exercise. Despite an
identical net area under the essential
amino acid curve, muscle protein
synthesis was elevated to a greater extent
after bolus supplementation than after
pulsed supplementation, and the
increased rate of synthesis following
bolus supplementation was related to
greater activation of signaling proteins in
the mTOR signaling pathway.129
Based on these results, we propose that
supplementing at 2 to 3 hour intervals
postexercise will maintain a relatively
rapid rate of muscle glycogen storage
and protein synthesis if supplementation
starts soon after the completion of
exercise. While the supplement must
contain sufficient amounts of
carbohydrate and protein, they need not
to be as high as used to initiate the
recovery process. It is important to note
American Journal of Lifestyle Medicine
Table 1.
Examples of Possible Timing of Workouts, Supplements, and Meals for 3 Different
Daily Training Schedules.a
Daily Workout Schedules
Time of Day
7:00 am
AM Workout
Breakfast
PM Workout
Breakfast
2×/Day Workouts
Breakfast
8:00 am
9:00 am
Workout
Workout
10:00 am
CP supplement
CP supplement
11:00 am
12:00 pm
Lunch
Lunch
CP snack
CP snack
Lunch
1:00 pm
2:00 pm
3:00 pm
4:00 pm
Workout
5:00 pm
6:00 pm
Workout
Dinner
CP supplement
7:00 pm
8:00 pm
CP supplement
Dinner
Protein snack
Dinner
9:00 pm
10:00 pm
Protein snack
Protein snack
a
Following prolonged, intense workouts, the postexercise supplement should provide sufficient carbohydrate to maximize muscle glycogen storage during the first hours of recovery (1.0 to 1.5 g kg−1
body wt) and contain between 20 and 30 g protein. For light to moderate intensity workouts, a light
carbohydrate (0.3 to 0.8 g kg−1 body wt)/protein (10 to 12 g protein) supplement is recommended.
Between-meal snacks should be approximately a 1:1 ratio of carbohydrate/protein and contain 100
to 200 kcal. The bedtime snack should contain approximately 20 g protein with minimal carbohydrate and fat. CP, carbohydrate protein.
that from a practical perspective, not all
feedings must be supplements. Exercise
training and nutrient supplementation
can be intermixed with regular daily
meals and snacks. Table 1 provides
eating schedules that accommodate
several different exercise-training
schedules. Even a snack before retiring
to bed can be an effective strategy to
optimize protein accretion.
Late night snacking is not normally
recommended. Research clearly shows
that obese individuals tend to skip
breakfast and eat the majority of their
daily calories from late afternoon to
bedtime.130-132 However, if one is trying
to build muscle and increase lean body
mass, a low-calorie protein supplement
before bedtime may help. Beelen et al
found that ingestion of a carbohydrate/
protein supplement following a late
afternoon resistance exercise session
increased protein synthesis for
approximately 2 hours.133 However,
protein synthesis was found to be
remarkably low during the sleeping
255
Jul • Aug 2014
American Journal of Lifestyle Medicine
hours. Res et al134 repeated the study by
Beelen et al,133 but provided a 40-g
casein supplement or placebo 30
minutes before bedtime. When the
casein supplement was provided, whole
body protein synthesis was increased
throughout the night and net protein
balance remained positive. In addition,
muscle protein synthesis also remained
elevated.134
Conclusions
Nutrient timing can have a dramatic
effect on exercise performance, recovery,
and training adaption. Carbohydrate
supplementation provided in the hours
before exercise can improve exercise
performance, and carbohydrate intake
during exercise can delay the onset of
fatigue and protect immune function.
Research suggests that the addition of
protein to an exercise supplement may
be more efficacious than carbohydrate
alone, and carbohydrate/protein
supplementation during exercise has the
added benefit of attenuating exerciseinduced muscle damage and soreness.
Carbohydrate/protein supplementation
immediately postexercise will significantly
increase the rate of muscle glycogen
synthesis, while delaying supplementation
for several hours will significantly slow
the rate of glycogen synthesis and its rate
of recovery. Supplementing with protein
or EAA postexercise will increase protein
synthesis and accretion, but again the
combination of carbohydrate plus protein
or EAA appears to be more efficacious. If
postexercise supplementation is
performed routinely and with the
appropriate protein/carbohydrate
mixture, it can have a significant
beneficial influence on body composition
and rate of training adaptation. The
principles of nutrient timing are relative
easy to implement and apply to
recreational exercisers and elite athletes
alike. AJLM
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