foods
Article
Postprandial Glucose Response after Consuming
Low-Carbohydrate, Low-Calorie Rice Cooked in a
Carbohydrate-Reducing Rice Cooker
Hyejin Ahn 1,† , Miran Lee 2,† , Hyeri Shin 1 , Heajung-angie Chung 3, * and Yoo-kyoung Park 4,5, *
1
2
3
4
5
*
†
Citation: Ahn, H.; Lee, M.; Shin, H.;
Chung, H.-a.; Park, Y.-k. Postprandial
Glucose Response after Consuming
Low-Carbohydrate, Low-Calorie Rice
Cooked in a Carbohydrate-Reducing
Rice Cooker. Foods 2022, 11, 1050.
https://doi.org/10.3390/
foods11071050
Department of Gerontology (AgeTech-Service Convergence Major), Kyung Hee University,
Yongin 17104, Korea; hjahn@khu.ac.kr (H.A.); zisoa@khu.ac.kr (H.S.)
Department of Medical Nutrition, Kyung Hee University, Yongin 17104, Korea; conan_6612@naver.com
Department of Korean Cuisine, Jeonju University, Jeonju 55069, Korea
Department of Medical Nutrition (AgeTech-Service Convergence Major), Kyung Hee University,
Yongin 17104, Korea
Department of Food Innovation and Health, Graduate School of East-West Medical Science,
Kyung Hee University, Yongin 17104, Korea
Correspondence: angiechung@jj.ac.kr (H.A.C.); ypark@khu.ac.kr (Y.K.P.);
Tel.: +82-63-220-2098 (H.A.C.); +82-31-201-3816 (Y.K.P.)
These authors contributed equally to this work.
Abstract: This study evaluates whether blood glucose response differs upon consuming rice
cooked in a carbohydrate (carb)-reducing rice cooker. Rice cooked this way exhibited 19% reduced
total carbohydrate (34.0 ± 0.3 vs. 27.6 ± 0.9 g/100 g rice) and 20% reduced total calorie
(149.0 ± 1.0 vs. 120.8 ± 3.7 kcal/100 g rice) contents. We measured the blood glucose response
(at 0, 15, 30, 45, 60, 90, and 120 min) in 13 healthy participants after consuming 6 different rice
types: regular white rice (regular WR, 50 g of available carbohydrate (AC)), low-carb WR with
equivalent weight as regular WR (low-carb WR (EW)), low-carb WR with equivalent carb as regular
WR (low-carb WR (EC), regular mixed-grain rice (regular MR), low-carb MR (EW) as regular MR,
and low-carb MR (EC) as regular MR. All rice samples were prepared in an electric carb-reducing
rice cooker. Postprandial blood glucose, sensory, and appetite were assessed after each test meal. The
incremental area under the curve of 15 and 30 min after rice consumption was significantly lower in
low-carb WR (EW) than that in regular WR. These results suggest possible health benefits of low-carb
WR in reducing early postprandial spikes in blood glucose level without significant differences in
satiety and satisfaction.
Academic Editor: Barry J. Parsons
Received: 27 February 2022
Accepted: 4 April 2022
Keywords: low-carb rice; carbohydrate-reducing rice cooker; blood glucose; sensory evaluation;
visual analog scale
Published: 6 April 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
1. Introduction
published maps and institutional affil-
Rice is globally among the most popular food grains and is currently consumed by
more than half of the global population [1,2]. White rice (WR), primarily consisting of starch,
is produced through a series of mechanized processes, including hulling and milling, and
it is globally the predominant rice type consumed [3,4]. The average glycemic index (GI) of
WR is higher than that of whole grains [5,6]. In addition, WR is the primary contributor
to dietary glycemic load (GL) in populations consuming rice as a staple food [6]. WR has
been turned into an unhealthy staple crop by the conclusions of repeated studies reporting
that it could lead to blood glucose increase and the development of type 2 diabetes mellitus
(T2D) [7,8]. In large-scale human observational studies among various populations and
several cohort studies, high GI food intake and high GL diets were associated with an
increased risk of developing T2D [9,10].
iations.
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Foods 2022, 11, 1050. https://doi.org/10.3390/foods11071050
https://www.mdpi.com/journal/foods
Foods 2022, 10, x FOR PEER REVIEW
Foods 2022, 11, 1050
2 of 13
of 13
Reducing carbohydrate (carb) intake is attracting growing attention from people2who
want to eat healthily [11]. Raising awareness of healthy eating and increasing the popularity of low-carb products in the growing global population could result in an expected
Reducing
(carb)
intake isperiod
attracting
growing attention
from people
who
market
growthcarbohydrate
rate of 6.40% in
the forecast
of 2020–2027
[12]. Reducing
carb intake
want to
healthily insulin
[11]. Raising
awareness
of healthy
andinincreasing
the popularity
helps
ineat
managing
resistance,
glycemia,
and eating
diabetes
patients with
diabetes
of low-carb
products
in theeffects
growing
population
could resultrisk
in an
expected
[13,14].
Related
beneficial
on global
body weight,
cardiovascular
indices,
andmarket
other
growth
rate
of
6.40%
in
the
forecast
period
of
2020–2027
[12].
Reducing
carb
intake
health indicators were also reported, even in people without diabetes [15,16]. WR helps
is an
in managing
insulin
and diabetes
patients
withJapan,
diabetes
important
staple
foodresistance,
in multipleglycemia,
Asian countries
such asinChina,
India,
and[13,14].
Korea
Related
effects
on bodya weight,
cardiovascular
risk indices,
and other
health
[17].
If it beneficial
is not possible
to suggest
WR substitute,
so it is necessary
to suggest
a healthier
indicators
were also
reported,
in people
diabetes
[15,16].
WR is an of
important
way
to consume
WR.
Recent even
efforts
aim to without
enable the
healthy
consumption
WR by
staple food
multiple
Asian countries such as China, India, Japan, and Korea [17]. If it
changing
itsin
cooking
method.
is notCarb-reducing
possible to suggest
a WR
so it is necessary
suggest
a healthier
wayReto
electric
rice substitute,
cookers theoretically
reducetostarch
contents
in rice.
consume
WR.
Recent
efforts
aim
to
enable
the
healthy
consumption
of
WR
by
changing
its
cently, with the increasing number of patients with diabetes and people who want to concooking
method.
sume
healthy
meals, the carb-reducing rice cooker is a promising device in the kitchen
Carb-reducing
rice cookers
reducerice
starch
contents
in rice. Recently,
appliance market. Inelectric
particular,
interesttheoretically
in carb-reducing
cookers
is growing
in Asia,
with
the
increasing
number
of
patients
with
diabetes
and
people
who
want
to
consume
where rice is the staple food. Various carb-reducing rice cookers are manufactured, and
healthy
the carb-reducing
rice
cooker
is a promising
in the kitchen
appliance
the
effectmeals,
of reducing
starch varies
from
a minimum
of 20%device
to a maximum
of 50%.
market. In particular, interest in carb-reducing rice cookers is growing in Asia, where rice
The basic principle of the carb-reducing rice cooker is to boil rice in excess water (3–
is the staple food. Various carb-reducing rice cookers are manufactured, and the effect of
4 times the weight of the rice), and starch contents from the rice are thus dissolved in the
reducing starch varies from a minimum of 20% to a maximum of 50%.
water and removed. Starch dissolved in rice is removed, resulting in low-carb rice. LowThe basic principle of the carb-reducing rice cooker is to boil rice in excess water
carb rice cookers are divided into two types, the siphon and wash-down types, according
(3–4 times the weight of the rice), and starch contents from the rice are thus dissolved in the
to the method of draining the excess water (Figure 1). The siphon-type carb-reducing rice
water and removed. Starch dissolved in rice is removed, resulting in low-carb rice. Lowcooker is characterized by a tray in the inner pot for cooking. As the inside of the rice
carb rice cookers are divided into two types, the siphon and wash-down types, according
cooker heats up rapidly, a pressure difference occurs in the inner pot. The pressure differto the method of draining the excess water (Figure 1). The siphon-type carb-reducing
ence pushes the water upward, and the water collects in the tray. After the excess water
rice cooker is characterized by a tray in the inner pot for cooking. As the inside of the
with the dissolved rice starch is removed on the tray, the rice is cooked the same way as
rice cooker heats up rapidly, a pressure difference occurs in the inner pot. The pressure
in a general rice cooker. The wash-down type carb-reducing rice cooker is characterized
difference pushes the water upward, and the water collects in the tray. After the excess
by
a basket
anddissolved
an innerrice
pot starch
that isisdeeper
than
inside
basket,
water
with the
removed
onthe
thebasket.
tray, theRice
riceisisput
cooked
thethe
same
way
and
the
bottom
of
the
inner
pot
is
filled
with
water
that
does
not
submerge
the
basket.
The
as in a general rice cooker. The wash-down type carb-reducing rice cooker is characterized
rice
is
cooked
by
placing
a
basket
of
it
in
the
inner
pot
filled
with
water.
As
the
inner
pot
by a basket and an inner pot that is deeper than the basket. Rice is put inside the basket,
is
heated,
boiling
repeatedly
splashes
into the
basket,
andsubmerge
the rice starch
dissolves
and
the bottom
of water
the inner
pot is filled
with water
that
does not
the basket.
The
into
the
water.
However,
there
are
some
complaints
that
the
wash-down
type
rice
contains
rice is cooked by placing a basket of it in the inner pot filled with water. As the inner
pot is
too
much
water.water repeatedly splashes into the basket, and the rice starch dissolves into
heated,
boiling
These
carb reduction
effects
claimed
by companies
are based on
food
the water. However,
there are
some
complaints
that the wash-down
type
ricecomposition
contains too
analysis,
and
no
clinical
research
data
are
available
on
the
effect
of
carb-reducing
rice conmuch water.
sumption on blood glucose response.
(a)
(b)
Figure
Figure 1.
1. Schematic
Schematic design
design of
of siphon
siphon and
and wash-down
wash-down carb-reducing
carb-reducing rice
rice cooker
cooker types.
types. (a)
(a) SiphonSiphontype
carb-reducing
rice
cooker
characterized
by
a
tray
in
the
inner
pot.
As
the
inside
rice
type carb-reducing rice cooker characterized by a tray in the inner pot. As the inside of the of
ricethe
cooker
cooker heats up rapidly, pressure difference occurs in the inner pot. (b) Wash-down type carb-reheats up rapidly, pressure difference occurs in the inner pot. (b) Wash-down type carb-reducing rice
ducing rice cooker displays a basket and an inner pot that is deeper than the basket.
cooker displays a basket and an inner pot that is deeper than the basket.
The
glucose
response after
consuming
carbohydrate-containing
food
relative
to a carThese
carb reduction
effects
claimed by
companies are based on
food
composition
bohydrate
reference
food,
typically
white
rice
or
write
bread,
is
normally
measured
using
analysis, and no clinical research data are available on the effect of carb-reducing
rice
the
glucose index
(GI). The
primary
purpose of this study was to determine whether lowconsumption
on blood
glucose
response.
carb The
rice cooked
a siphon-type
carb-reducing
rice cooker could reduce
glucose
glucosein
response
after consuming
carbohydrate-containing
foodblood
relative
to a
response
in
healthy
adults.
The
secondary
purpose
was
to
perform
sensory
and
appetite
carbohydrate reference food, typically white rice or write bread, is normally measured
evaluation
after low-carb
riceThe
consumption.
using the glucose
index (GI).
primary purpose of this study was to determine whether
low-carb rice cooked in a siphon-type carb-reducing rice cooker could reduce blood glucose
Foods 2022, 11, 1050
Foods 2022, 10, x FOR PEER REVIEW
3 of 13
3 of 13
response in healthy adults. The secondary purpose was to perform sensory and appetite
2. Materials
andafter
Methods
evaluation
low-carb rice consumption.
2.1. Study Design
2. Materials and Methods
This study was conducted to evaluate how consuming low-carb rice cooked in a carb2.1. Study Design
reducing rice cooker affects blood glucose response and appetite, and to perform sensory
This
study
was
conducted
to in
evaluate
how consuming
low-carb rice
cooked in
a carbevaluation.
The
study
was
conducted
accordance
with the Declaration
of Helsinki,
and
reducing
rice
cooker
affects
blood
glucose
response
and
appetite,
and
to
perform
sensory
the protocol was approved by the Ethics Committee of the Institutional Review Board
evaluation.
was conducted
in accordance
with the Declaration of Helsinki, and
(IRBs)
of Kyung The
Heestudy
University
in September
2021 (no. KHGIRB-21-420).
the protocol was approved by the Ethics Committee of the Institutional Review Board
(IRBs)Participants
of Kyung Hee University in September 2021 (no. KHGIRB-21-420).
2.2. Study
We Study
recruited
13 healthy participants (4 men and 9 women) from the campus and the
2.2.
Participants
community. The inclusion criterion was being at least 35 years old. Exclusion criteria were
We recruited 13 healthy participants (4 men and 9 women) from the campus and the
as follows: patients with uncontrolled diabetes abd people unable to perform a fingercommunity. The inclusion criterion was being at least 35 years old. Exclusion criteria were
prick blood test due to psychological fear. All subjects gave their informed consent to paras follows: patients with uncontrolled diabetes abd people unable to perform a finger-prick
ticipate in the study before starting.
blood test due to psychological fear. All subjects gave their informed consent to participate
in the study before starting.
2.3. Test Rice Preparation
RiceTest
samples
were cooked in a carb-reducing electric rice cooker (CALOFREE CFRC2.3.
Rice Preparation
IH600, CADEAUS
Co., Ltd.,
South
The carb-reducing
ricecooker
cooker(CALOFREE
used in
Rice samples
were Seoul,
cooked
in aKorea).
carb-reducing
electric rice
the study
was
a
siphon
type
having
the
same
composition
as
that
of
an
electric
rice
cookerused
CFRC-IH600, CADEAUS Co., Ltd., Seoul, Korea). The carb-reducing rice cooker
within
only
inclusion
a traytype
(Figure
2). When
cooking
in regularasrice
tray rice
thethe
study
was a of
siphon
having
the same
composition
thatmode,
of an the
electric
was cooker
not placed
the the
inner
pot for cooking;
was 2).
only
whencooking
using the
carb-reducing
withononly
inclusion
of a tray this
(Figure
When
in regular
rice mode,
rice the
mode.
rice
is an
heating
ricecarbtrayThis
wassiphon-type
not placed on
thecooker
inner pot
forinduction
cooking; this
was (IH)
only nonpressure
when using the
cooker
with the
of asiphon-type
regular ricerice
cooker.
It is
was
a nonpressure
IH
reducing
ricefunction
mode. This
cooker
an designed
induction as
heating
(IH) nonpressure
system
because
boiling
water
must
freely
splash
up
and
down
inside
the
rice
cooker
to IH
rice cooker with the function of a regular rice cooker. It was designed as a nonpressure
cooksystem
low-carb
rice. The
IH system
heatssplash
the inner
pot to
highinside
heat. This
boils
the to
because
boiling
water quickly
must freely
up and
down
the rice
cooker
water
quickly,
allowing
for IH
thesystem
starch quickly
to dissolve
theinner
water
the
riceThis
is overcook
low-carb
rice. The
heatsinthe
potbefore
to high
heat.
boils the
cooked,
and
createsallowing
a high pressure
difference
in the in
inner
effectively
excess
water
quickly,
for the starch
to dissolve
the pot,
water
before thepushing
rice is overcooked,
water
upcreates
through
the tray.
Afterdifference
the rice isincooked,
thepot,
water
accumulated
in excess
the tray
and
a high
pressure
the inner
effectively
pushing
water
up be
through
the tray. After the rice is cooked, the water accumulated in the tray should
should
removed.
be removed.
(a)
(b)
Figure
2. Composition
of a siphon-type
carb-reducing
rice cooker.
(a) Carb-reducing
rice cooker
Figure
2. Composition
of a siphon-type
carb-reducing
rice cooker.
(a) Carb-reducing
rice cooker
component;
(b)
Appearance
after
cooking
low-carb
rice.
component; (b) Appearance after cooking low-carb rice.
Rice Rice
(white
rice (WR):
polished
rice 300
g; 300
mixed-grain
rice (MR):
g polished
rice
(white
rice (WR):
polished
rice
g; mixed-grain
rice210
(MR):
210 g polished
+ 90 rice
g mixed-grain
rice) was
washed
three times
distilled
waterwater
[18–20].
+ 90 g mixed-grain
rice)
was washed
three with
timessufficient
with sufficient
distilled
[18–20].
Low-carb
rice samples
werewere
cooked
withwith
a water/rice
ratioratio
(W/R)
of 4.0of(1200
mL) without
Low-carb
rice samples
cooked
a water/rice
(W/R)
4.0 (1200
mL) without
immersing
in water
in the
low-carb
ricerice
mode
of of
the
rice
immersing
in water
in the
low-carb
mode
the
ricecooker
cookerfor
for35–45
35–45min.
min. General
General rice
rice samples
samples were
were cooked
cooked with
with aa W/R
W/Rratio
ratioofof1.2
1.2(300
(300mL)
mL)after
aftersoaking
soakingthe
therice
riceininwater
water for
30min
minin
inthe
the general
general rice mode of the
for 30
the rice
rice cooker
cookerfor
for45–50
45–50min.
min.The
Themultigrain
multigrainused
usedin the
in the study was a commercially available 11 Mixed Grains (Daesang Agricultural
Foods 2022, 11, 1050
Foods 2022, 10, x FOR PEER REVIEW
4 of 13
4 of 13
study was a commercially available 11 Mixed Grains (Daesang Agricultural Farming Corp.
Farming
Co.,
LTD.,
South
Korea), which
is composed
of glutinous,
Co., LTD.,
Wanju,Corp.
Korea),
which
is Wanju,
composed
of glutinous,
brown,
glutinous brown,
black brown,
glutinous
brown,
black
glutinous
brown,
red–brown,
green–brown,
red–brown,
glutinous brown, red–brown, green–brown, red–brown, compressed, and sticky barley rice, comand sticky
rice,rice
and
two
typeautomatically
of millet rice.cooked,
After the
rice had
been autoand twopressed,
type of millet
rice. barley
After the
had
been
it was
left on
matically
cooked,
it
was
left
on
the
warm
setting
for
an
additional
8
min
and
mixed
well.
the warm setting for an additional 8 min and mixed well. Figure 3 presents the weight
Figure
3
presents
the
weight
change
diagram
of
rice
and
water
before
and
after
cooking.
change diagram of rice and water before and after cooking. The test rice was cooked in the
The
test rice
cooked
in the
Nutrition Living Lab at Kyung Hee University.
Nutrition
Living
Labwas
at Kyung
Hee
University.
(a)
(b)
Figure 3. Weight change diagram of rice and water before and after cooking: (a) regular rice; (b) low3. Weight
change
diagram
ricewater/rice
and water(W/R)
beforeratios
and after
(a)without
regular rice; (b)
carb rice. Figure
Low-carb
rice samples
were
cookedofwith
of 4.0cooking:
(1200 mL)
low-carb
rice.
Low-carbrice
ricemode
samples
were
water/rice
(W/R) ratios
of 4.0 (1200 mL)
immersion
in water
in low-carb
of the
ricecooked
cooker with
for 35–45
min. General
rice samples
without
water
low-carb
rice mode
of the
rice cooker
General rice
were cooked
with immersion
W/R ratios in
of 1.2
(300inmL)
after soaking
the rice
in water
for 30 for
min35–45
in themin.
‘general
samples were cooked with W/R ratios of 1.2 (300 mL) after soaking the rice in water for 30 min in
rice mode’ of the rice cooker for 45–50 min. White rice (WR): 300 g polished rice; mixed-grain rice
the ‘general rice mode’ of the rice cooker for 45–50 min. White rice (WR): 300 g polished rice; mixed(MR): 210 g polished rice + 90 g mixed-grain rice).
grain rice (MR): 210 g polished rice + 90 g mixed-grain rice).
2.4. Test Rice Nutrient Analysis
2.4. Test Rice Nutrient Analysis
The cooked rice was gently fluffed with a spatula and transferred into a container
cooked
riceanalysis.
was gently
fluffed
withrice
a spatula
and
into ade
container
with a plasticThe
lid for
nutrient
Freshly
cooked
was sent
to transferred
Société Générale
with(SGS,
a plastic
lid for
nutrient
analysis.analysis.
Freshly cooked rice was sent to Société Générale de
Surveillance
Seoul,
Korea)
for nutrient
Surveillance (SGS, Seoul, South Korea) for nutrient analysis.
2.5. Study Procedure
2.5. Study
Subjects
wereProcedure
provided with a verbal explanation of the study and directed to follow
the instructions
on thewere
study
description
Participants
were
instructed
to fastto follow
Subjects
provided
with document.
a verbal explanation
of the
study
and directed
overnight
12 h before
participation
in the
study. Participants
In addition, were
subjects
were to fast
thefor
instructions
on their
the study
description
document.
instructed
encouraged
to eat their
mealstheir
andparticipation
conduct theirin
daily
day before
theirwere enovernight
for 12usual
h before
the activities
study. In the
addition,
subjects
participation.
The
participants
visited
the
living
lab
7
times,
consumed
6
types
of
couraged to eat their usual meals and conduct their daily activities the day test
before their
foods, and
performed aThe
finger-prick
blood
glucose
visual
(VAS) test
for of test
participation.
participants
visited
the test,
living
lab 7analog
times,scale
consumed
6 types
the assessment
of
hunger,
feeling
of
fullness,
and
desire
to
eat,
and
sensory
evaluation.
foods, and performed a finger-prick blood glucose test, visual analog scale (VAS) test for
We the
followed
the official
method
for of
determining
thedesire
GI into
foods
instructed
the
assessment
of hunger,
feeling
fullness, and
eat, and
sensoryby
evaluation.
OrganizationWe
for followed
International
Standardization
(ISO)
[21,22] Participants
were tested
for by the
the official
method for
determining
the GI in foods
instructed
oral glucose
tolerance
at
the
first
visit,
followed
by
six
visits
to
participate
in
each
food
Organization for International Standardization (ISO) [21,22] Participants were tested for
testing session.
All tests
were conducted
approximately
a.m.–12:00
p.m. Blood
oral glucose
tolerance
at the first at
visit,
followed by 09:00
six visits
to participate
in each food
glucose testing
levels were
tested
on
an
empty
stomach
(0
min)
and
at
15,
30,
45,
60, 90, and
session. All tests were conducted at approximately 09:00 a.m.–12:00
p.m. Blood
120 min glucose
after testlevels
food were
consumption.
individuals
fasting
levels
below
tested on Only
an empty
stomachwith
(0 min)
andglucose
at 15, 30,
45, 60,
90, and 120
110 mg/dL
in the study. Only individuals with fasting glucose levels below 110
mincould
after participate
test food consumption.
Themg/dL
six testcould
rice types
were as
(1) regular WR (147 g one small bowl, 50 g of
participate
infollows:
the study.
available carbohydrate
(AC)),
(2)
low-carb
WR
with equivalent
(EW)
as regular
WR 50 g of
The six test rice types were as follows:
(1) regularweight
WR (147
g one
small bowl,
(147 g serving,
40
g
AC),
(3)
low-carb
WR
with
equivalent
carb
(EC)
as
regular
WR
(181
g regular
available carbohydrate (AC)), (2) low-carb WR with equivalent weight (EW) as
WR (147 g serving, 40 g AC), (3) low-carb WR with equivalent carb (EC) as regular WR
Foods 2022, 11, 1050
5 of 13
serving, 50 g AC), (4) regular MR (144 g one small bowl, 50 g AC), (5) low-carb MR (EW)
(144 g serving, 40 g AC), and (6) low-carb MR (EC) (181 g serving, 50 g AC).
The blood glucose levels of participants were measured with the finger-prick method
using an Accu-Chek Performa Blood Glucose Meter (Accu-Chek, USA). Each blood glucose
level after the test meals was used to calculate the incremental area under the curve
(iAUC) [23].
2.6. Sensory Evaluation
Participants rated the six types of cooked rice for intensities of individual attributes,
including appearance, flavor, taste, texture properties, and overall preference, on a 9-point
structured scale (1 = extremely low intensity and 9 = extremely high intensity) [24]. Cooked
rice samples of approximately 15 g were prepared in plastic containers and tested by
the panelists. Samples were coded with random three-digit numbers. Participants were
presented with six samples in random order on a tray with a glass of drinking water at each
testing session. Samples were served warm, and participants were instructed to cleanse
their palates with water prior to testing a new sample. Glossiness, color, and intactness
were first evaluated as appearance characteristics of the cooked rice. The flavor was roasted
and nutty, and it smelled like deliciously cooked rice, but smelled undercooked before
putting it into the mouth. The test foods were evaluated for sweetness, roasted nutty flavor,
and overall taste. During the few first bites, springiness, chewiness, and moistness were
assessed by compressing the sample between the molars and evaluating the force required
to bite through the sample. The adhesiveness and cohesiveness of the cooked rice mass
were evaluated during the chewing stage as the degree to which the sample adhered to the
teeth or palate.
2.7. Hunger and Appetite Evaluation
For the assessment of hunger, desire to eat (DTE), and feeling of fullness, we used
validated VAS [25]. Participants were asked to rate their levels of hunger (“How hungry
do you feel at this moment?”), DTE (“How strong is your desire to eat at this moment?”),
and feeling of fullness (“How full does your stomach feel at this moment?”), using these
scales presented one at a time. Subjects marked their rating on a 100 mm line anchored at 0
(“I am not hungry/satiated at all”; “I have no desire to eat at all”) and 100 (“I have never
been hungry/satiated”; “I have never had more desire to eat”). These evaluations were
performed by participants before consuming the test meals (basal time, 0 min) and were
repeated after the end of the meal at 60 min intervals over a total period of 180 min (0, 60,
120, and 180 min).
2.8. Anthropometric Measures
Height, body mass index, and body composition were measured using a stadiometer
(BSM330, Inbody, Seoul, Korea) and bioimpedance (Inbody770, Seoul, Korea). Participants
stood barefoot with minimal clothes on in a straight position, and palms were facing the
thighs, so that the posture was clear.
2.9. Sample Size and Statistical Analysis
Sample size was determined on the basis of the method of the International Organization for Standardization [18]. This suggests that using 10 subjects to measure glycemic
response to a single food could exhibit adequate power and accuracy.
All data are expressed as mean ± standard deviation (SD) values. The iAUC and
blood glucose responses were analyzed at each test time using an independent Student’s
t-test. Statistical analysis was performed using the IBM SPSS 25 statistical program (IBM,
New York, NY, USA). Statistical significance was set at p-values of p < 0.05.
Foods 2022, 11, 1050
6 of 13
3. Results
3.1. Participants
Of the 17 screened participants, 13 eligible (4 males and 9 females) were selected.
Table 1 shows the baseline characteristics of the participants who completed the study.
Table 1. Characteristic of subjects.
Classification
Subjects (n = 13)
56.8 ± 12.1 1
4/9
162.2 ± 10.6
64.7 ± 14.7
24.5 ± 4.4
32.4 ± 5.3
24.0 ± 6.9
0.90 ± 0.05
99.5 ± 15.0 (82–120)
Age (years)
Sex (male/female)
Height (cm)
Body weight (kg)
Body mass index (kg/m2 )
% Body fat (%)
Skeletal muscle mass (kg)
Waist–hip ratio
Fasting blood glucose (mg/dL, range)
1
Data are mean ± standard deviation (SD).
3.2. Test Food Nutrient Contents
Table 2 presents the nutrient contents of the test meals. Compared with regular
rice, low-carb rice had less carbohydrate (regular WR: 34.0 ± 0.3; regular MR:
34.8 ± 0.4 vs. low-carb WR: 27.6 ± 0.9; low-carb MR: 28.0 ± 1.4) and less energy (regular
WR: 149.0 ± 1.0; regular MR: 154.4 ± 2.3 vs. low-carb WR: 120.8 ± 3.7; low-carb MR:
129.3 ± 2.9). The moisture content of low-carb rice was higher than that of regular rice
(regular WR: 62.9 ± 0.3; regular MR: 61.6 ± 0.4 vs. low-carb WR: 70.1 ± 0.8; low-carb MR:
68.0 ± 0.6).
Table 2. Test food compositions.
Test Food
Energy
(kcal/100 g)
Carbohydrate
(g/100 g)
Protein
(g/100 g)
Fat
(g/100 g)
Ash
(g/100 g)
Dietary Fiber
(g/100 g)
Water
(g/100 g)
Regular WR
Low-carb WR
Regular MR
Low-carb MR
149.0 ± 1.0 1
120.8 ± 3.7 *
154.4 ± 2.3
129.3 ± 2.9 **
34.0 ± 0.3
27.6 ± 0.9 *
34.8 ± 0.4
28.0 ± 1.4 **
2.6 ± 0.0
1.7 ± 0.8
2.9 ± 0.1
3.3 ± 1.0
0.4 ± 0.0
0.5 ± 0.1
0.5 ± 0.1
0.6 ± 0.2
0.1 ± 0.0
0.1 ± 0.0
0.2 ± 0.0
0.2 ± 0.0
0.4 ± 0.0
0.4 ± 0.0
0.5 ± 0.0
0.5 ± 0.0
62.9 ± 0.3
70.1 ± 0.8 *
61.6 ± 0.4
68.0 ± 0.6 **
WR, white rice; MR, mixture of mixed grains to WR (WR/MR ratio is 7:3). All experiments were carried out in
triplicate and repeated 3 times. 1 Data represent mean ± standard deviation (SD) calculated by data of cooked
rice. * p < 0.01 compared to regular WR; ** p < 0.01 compared to regular MR, after independent t-test.
3.3. Incremental Area under Glucose Curve (iAUC Blood Glucose) of Test Foods
Figure 4 shows the iAUC blood glucose of the test foods. Blood glucose iAUC after
low-carb WR (EW) intake was significantly lower at the time points of 0–15 and 0–30 min
compared to regular WR (0–15 min: p < 0.05; 0–30 min: p < 0.05). However, no significant
difference could be observed in iAUC blood glucose between regular MR and low-carb MR.
3.4. Postprandial Blood Glucose Changes after Test Food Consumption
Table 3 shows postprandial blood glucose changes after test food consumption. Compared with regular rice, average blood glucose levels at each time after eating low-carb rice
were low. However, no significant difference could be observed in blood glucose levels
among test foods.
8000
8000
7000
7000
6000
6000
5000
5000
4000
4000
3000
3000
2000
2000
1000
1000
0
0
7 7ofof13
13
7 of 13
glucose
bloodglucose
iAUCblood
iAUC
glucose
bloodglucose
iAUCblood
iAUC
Foods
FOR PEER REVIEW
Foods2022,
2022,10,
11,xx1050
Foods
10,
FOR PEER REVIEW
0-15 min 0-30 min 0-45 min 0-60 min 0-90 min 0-120 min
0-15 min 0-30 min 0-45 min 0-60 min 0-90 min 0-120 min
Regular WR
Regular WR
Low-carb WR (EW)
Low-carb WR (EW)
Low-carb WR (EC)
Low-carb WR (EC)
(a)
(a)
8000
8000
7000
7000
6000
6000
5000
5000
4000
4000
3000
3000
2000
2000
1000
1000
0
0
0-15 min 0-30 min 0-45 min 0-60 min 0-90 min 0-120 min
0-15 min 0-30 min 0-45 min 0-60 min 0-90 min 0-120 min
Regular MR
Regular MR
Low-carb MR (EW)
Low-carb MR (EW)
Low-carb MR (EC)
Low-carb MR (EC)
(b)
(b)
Figure
Figure4.4.
4.Incremental
Incrementalarea
areaunder
underglucose
glucosecurve
curveof
oftest
testfoods
foodsSignificant
Significantdifferences
differencesby
byindependent
independent
Figure
Incremental
area
under
glucose
curve
of
test
foods
Significant
differences
by
independent
t-test between regular WR iAUC and low-carb WR (EW) iAUC indicated with ◆ (p < 0.05). EC,
t-test
between
regular
WR
iAUC
and
low-carb
WR
(EW)
iAUC
indicated
with
(p
0.05). EC,
EC,
t-test between regular WR iAUC
◆
<< 0.05).
equivalent carbohydrate as regular rice; EW, equivalent weight as regular rice; iAUC, incremental
equivalent
carbohydrate
as
regular
rice;
EW,
equivalent
weight
as
regular
rice;
iAUC,
incremental
equivalent carbohydrate as regular rice; EW, equivalent weight as regular rice; iAUC, incremental
area under the curve; WR, white rice; MR, mixture of mixed grains to WR (WR/MR ratio is 7:3). (a)
area
the
curve;
ofof
mixed
grains
to to
WR
(WR/MR
ratioratio
is 7:3).
(a)
area under
under
theMixed-grain
curve;WR,
WR,white
whiterice;
rice;MR,
MR,mixture
mixture
mixed
grains
WR
(WR/MR
is 7:3).
White
rice; (b)
rice.
White
rice;
(b)
Mixed-grain
rice.
(a) White rice; (b) Mixed-grain rice.
Test Foods (Serving)
Glucose (50 g)
Regular WR
Low-carb WR (EW)
Low-carb WR (EC)
Regular MR
Low-carb MR (EW)
Low-carb
MR (EC)
Test
Foods (Serving)
Test Foods (Serving)
Glucose (50 g)
Glucose (50 g)
Regular WR
Regular WR
Low-carb WR (EW)
Low-carb WR (EW)
Low-carb WR (EC)
Low-carb WR (EC)
Regular MR
Regular MR
Low-carb MR (EW)
Low-carb MR (EW)
Low-carb MR (EC)
Low-carb MR (EC)
3.4.
Postprandial
Blood
Glucose
Changes
after
Test
Food Consumption
3.4.
Postprandial
Blood
Glucose
Changes
after
Test
Consumption
Table
3. Postprandial
blood
glucose
changes
after
theFood
consumption
of test foods.
Table
3
shows
postprandial
blood
glucose
changes
Table 3 shows postprandial blood glucose changesafter
aftertest
testfood
foodconsumption.
consumption.ComCompared
with
regular
rice,
average
blood
glucose
levels
at
each
time
after
Blood Glucose
Each Time
(mg/dL)
pared with regular rice, average
bloodatglucose
levels
at each time after eating
eating low-carb
low-carb
rice
no
could
be
in
0rice
minwere
15However,
min
30 significant
min
45
min
60 min
90 min
120 min levwerelow.
low.
However,
no
significantdifference
difference
could
beobserved
observed
inblood
bloodglucose
glucose
levels±among
test
1
135.7
±
26.8
164.2 ± 32.2
165.2 ± 43.9
169.8 ± 50.4
156.8 ± 61.2
130.9 ± 55.6
101.1els
15.2
among
testfoods.
foods.
99.6 ± 13.8
112.7 ± 12.4
144.9 ± 17.6
159.0 ± 31.0
161.8 ± 41.7
157.1 ± 44.6
99.7
± 12.3
105.3 ± 11.4blood
139.8
± 22.0changes
149.3after
± 25.3
158.8 ± 37.4 of test
139.7foods.
± 46.9
Table
3. Postprandial
glucose
the consumption
Table 3. Postprandial
blood
glucose changes
after the consumption
of 138.6
test foods.
99.5 ± 17.1
116.5 ± 33.0
143.6 ± 24.0
158.8 ± 38.7
146.1 ± 34.6
± 41.1
100.5 ± 16.4
107.5 ± 18.0
141.4 ± 25.8
153.4
± 31.8
155.4 ± 43.7
145.2 ± 38.7
(mg/dL)
(mg/dL)
96.5 ± 13.9
105.8 ± 14.6
140.8 ±
23.9 Glucose
154.9 ±at
32.0
147.2 ± 32.1
141.2 ± 46.6
Blood
Each Time
at Each149.7
Time± 43.0
100.6 ± 19.4
110.3 ± 21.1
147.7 ±Blood
30.2 Glucose
153.5 ± 39.4
139.5 ± 44.4
141.5 ± 40.1
133.9 ± 42.1
130.2 ± 40.0
132.3 ± 46.5
123.5 ± 35.1
132.5 ± 45.8
0 min
15 min
30 min
45 min
60 min
90 min
120 min
01 min represent15mean
min
30 min
45 min
min
90 min Regular120
(SD)
were not60
significantly
different.
WRmin
(147 g),
101.1 ±Data
15.2 11 135.7 ± 26.8± standard
164.2 ±deviation
32.2
165.2
±and
43.9
169.8
± 50.4
156.8
± 61.2
130.9
± 55.6
101.1low-carb
± 15.2 WR135.7
26.8
± 32.2
165.2
± g)
43.9
169.850,
± 50.4
156.8
± 61.2
130.9
± 55.6
(EW, ±
147
g), and164.2
low-carb
WR (EC,
181
contained
40, and 50
g carbohydrate,
respectively.
99.6Carbohydrate
± 13.8
112.7
± 12.4
144.9
± (144
17.6
159.0 ± 31.0
161.8
± 41.7
157.1 MR
± 44.6
141.5
± 40.1
content
of regular
MR
144 g),
(EC, 179
g) was
50, 40,
99.6 ± 13.8
112.7
± 12.4
144.9
± 17.6g), low-carb
159.0 ± MR
31.0(EW,161.8
± and
41.7low-carb
157.1 ± 44.6
141.5
± 40.1
50 g, respectively.
EC, equivalent
carbohydrate
regular158.8
rice; EW,
equivalent
99.7and
± 12.3
105.3 ± 11.4
139.8 ± 22.0
149.3 ±as25.3
± 37.4
139.7weight
± 46.9 as regular
133.9 ±rice;
42.1WR,
99.7white
± 12.3
105.3
±
11.4
139.8
±
22.0
149.3
±
25.3
158.8
±
37.4
139.7
±
46.9
133.9
±
42.1
rice; MR,
mixture
grains
to WR158.8
(WR/MR
is 7:3).± 34.6
99.5 ± 17.1
116.5
± 33.0of mixed
143.6
± 24.0
± 38.7ratio 146.1
138.6 ± 41.1
130.2 ± 40.0
99.5 ± 17.1
116.5 ± 33.0
143.6 ± 24.0
158.8 ± 38.7
146.1 ± 34.6
138.6 ± 41.1
130.2 ± 40.0
100.5 ± 16.4
107.5 ± 18.0
141.4 ± 25.8
153.4 ± 31.8
155.4 ± 43.7
145.2 ± 38.7
132.3 ± 46.5
100.5 ± 16.4
107.5 ± 18.0
141.4 ± 25.8
153.4 ± 31.8
155.4 ± 43.7
145.2 ± 38.7
132.3 ± 46.5
Sensory
Evaluation
96.53.5.
± 13.9
105.8
± 14.6
140.8 ± 23.9
154.9 ± 32.0
147.2 ± 32.1
141.2 ± 46.6
123.5 ± 35.1
96.5 ± 13.9
105.8 ± 14.6
140.8 ± 23.9
154.9 ± 32.0
147.2 ± 32.1
141.2 ± 46.6
123.5 ± 35.1
100.6 ± 19.4
110.3
± 21.1 analysis
147.7 ±could
30.2
153.5 ± 39.4evaluate
149.7 ±the
43.0quality
139.5of± the
44.4
132.5 ±rice
45.8
Sensory
profile
100.6 ± 19.4
110.3
± 21.1
147.7 ± 30.2 objectively
153.5 ± 39.4
149.7 ± 43.0
139.5 ± 44.4low-carb
132.5 ± 45.8by
1 Data represent mean ± standard deviation (SD) and were not significantly different. Regular WR
quantifying
appearances,
flavor,
taste,
texture
properties,
and
overall
preference.
Table
1 Data represent mean ± standard deviation (SD) and were not significantly different. Regular WR 4
(147
g), low-carb
WR (EW,
147 g), and
low-carb WR (EC, 181 g) contained 50, 40, and 50 g carbodisplays
the sensory
evaluation
results.
(147
g), low-carb
WR (EW,
147 g), and
low-carb WR (EC, 181 g) contained 50, 40, and 50 g carbohydrate, respectively. Carbohydrate content of regular MR (144 g), low-carb MR (EW, 144 g), and
hydrate, respectively. Carbohydrate content of regular MR (144 g), low-carb MR (EW, 144 g), and
low-carb
(EC, 179 g) was of
50,test
40,foods.
and 50 g, respectively. EC, equivalent carbohydrate as regular
Table 4. MR
Sensory
low-carb
MR (EC,evaluation
179 g) was 50,
40, and 50 g, respectively. EC, equivalent carbohydrate as regular
rice; EW, equivalent weight as regular rice; WR, white rice; MR, mixture of mixed grains to WR
rice; EW, equivalent weight as regular rice; WR, white rice; MR, mixture of mixed grains to WR
(WR/MR ratio is 7:3).
Texture
Overall
(WR/MR
ratio is 7:3).
Test Foods
Appearances
Flavor
Taste
Properties
Preference
Regular
WR
4.7 ± 2.2
5.8 ± 1.6
5.6 ± 2.0
6.7 ± 1.2
5.7 ± 1.7
3.5.
Sensory
3.5.
SensoryEvaluation
Evaluation
Low-carb WR
6.4 ± 1.5
5.1 ± 2.3
5.8 ± 1.5
5.4 ± 2.1
6.3 ± 1.2
Sensory
analysis
objectively
evaluate
the
Regular
MR profile
± 1.6 could
± 1.9
5.4 ± 1.5the
5.4 of
±
5.9 ±rice
1.7 by
Sensory
profile6.1
analysis
could4.9
objectively
evaluate
thequality
quality
of1.9
thelow-carb
low-carb
rice
by
Low-carb MR
6.4 ± 1.5flavor, taste,
5.1 ± texture
2.2
5.9 ± 1.6 and overall
5.5 ± 1.8
6.5 Table
± 1.5 4
quantifying
appearances,
properties,
preference.
quantifying appearances, flavor, taste, texture properties, and overall preference. Table 4
1 Data represent
displays
the
evaluation
results.
mean ± standard
deviation
(SD), were calculated by data of cooked rice, and were not significantly
displays
thesensory
sensory
evaluation
results.
different.
Appearance
of test foods evaluated
by their
glossiness,
color,
intactness. Flavor investigated
by
The
sensory
evaluation
of
low-carb
rice
cooked
in and
aa carb-reducing
rice cooker
The degree
sensory
evaluation
of flavor
low-carb
ricerice,
cooked
carb-reducing
cooker
examining
of roasted
nutty flavor,
of cooked
and smellinof undercooked
rice. Testrice
food taste
was
showed
significant
difference
with
regular
appearance
color,
evaluatedno
by sweet
taste, roasted
nutty flavor,
overall rice
taste.
Texture
properties(glossiness,
of test foods investigated
by
showed
no
significant
difference
withand
regular
rice in
in
appearance
(glossiness,
color, and
and
examining degree
of springiness,
chewiness,
adhesiveness,
cohesiveness,
and
moistness.
WR,
white rice; MR,
intactness),
flavor
(roasted
nutty
flavor,
flavor
of
cooked
rice,
and
smell
of
undercooked
intactness),
flavor
(roasted
nutty flavor,
flavor of cooked rice, and smell of undercooked
mixture of mixed
grains to WR
(WR/MR ratioflavor,
is 7:3).
rice),
rice),taste
taste(sweet
(sweettaste,
taste,roasted
roastednutty
nutty flavor,and
andoverall
overalltaste),
taste),texture
textureproperties
properties(spring(springiness,
chewiness,
adhesiveness,
cohesiveness,
and
moistness),
and
overall
iness, chewiness, adhesiveness, cohesiveness, and moistness), and overallpreference.
preference.
1
Texture
Overa
Properties
Prefere
Regular WR
5.7 ± 1.7 1
4.7 ± 2.2
5.8 ± 1.6
5.6 ± 2.0
6.7 ± 1
Low-carb WR
6.4 ± 1.5
5.1 ± 2.3
5.8 ± 1.5
5.4 ± 2.1
6.3 ± 1
Regular MR
6.1 ± 1.6
4.9 ± 1.9
5.4 ± 1.5
5.4 ± 1.9
5.9 ± 1
8 of 13
Low-carb MR
6.4 ± 1.5
5.1 ± 2.2
5.9 ± 1.6
5.5 ± 1.8
6.5 ± 1
1 Data represent mean ± standard deviation (SD), were calculated by data of cooked rice, and
not significantly different. Appearance of test foods evaluated by their glossiness, color, and i
The sensory evaluation of low-carb rice cooked in a carb-reducing rice cooker showed
ness. Flavor investigated by examining degree of roasted nutty flavor, flavor of cooked rice
no significantsmell
difference
with regular
ricefood
in appearance
(glossiness,
color,
intactof undercooked
rice. Test
taste was evaluated
by sweet
taste,and
roasted
nutty flavor
ness), flavor (roasted
nutty
flavor,
flavor
of
cooked
rice,
and
smell
of
undercooked
rice),of spring
overall taste. Texture properties of test foods investigated by examining degree
taste (sweet taste,
roasted
nutty flavor,
and overall
taste),
texture
properties
chewiness,
adhesiveness,
cohesiveness,
and
moistness.
WR,
white rice;(springiness,
MR, mixture of mixed g
chewiness, adhesiveness,
cohesiveness,
and
moistness),
and
overall
preference.
to WR (WR/MR ratio is 7:3).
Test Foods
Foods 2022, 11, 1050
Appearances
Flavor
Taste
3.6. Hunger and
3.6.Appetite
HungerEvaluation
and Appetite Evaluation
Change in hunger,
feeling
of fullness,
and
desire and
to eat
aftertolow-carb
rice intake
Change in hunger,
feeling of
fullness,
desire
eat after low-carb
rice intake
were evaluated
using
the
VAS
(Figure
5).
The
VAS
test
showed
no
significant
difference
evaluated using the VAS (Figure 5). The VAS test showed no significant
difference in
in hunger, feeling
of fullness,
and desire
to eattofor
h after
consuming
of low-carb
ricerice comp
ger, feeling
of fullness,
and desire
eat3for
3 h after
consuming
of low-carb
compared to regular
rice.
to regular rice.
(a)
(b)
(c)
Figure
5. Change
in hunger,
fullness,
and
desire
to eat analog
using ascale.
visualEC,
analog
scale. EC, equiv
Figure 5. Change
in hunger,
fullness,
and desire
to eat
using
a visual
equivalent
carbohydrate as regular rice; EW, equivalent weight as regular rice; WR, white rice; VAS, v
carbohydrate as regular rice; EW, equivalent weight as regular rice; WR, white rice; VAS, visual
analog scale; MR, mixture of mixed grains to WR (WR/MR ratio is 7:3). Data were not signific
analog scale; MR, mixture of mixed grains to WR (WR/MR ratio is 7:3). Data were not significantly
different. (a) Hunger; (b) Feeling of fullness; (c) Desire to eat.
different. (a) Hunger; (b) Feeling of fullness; (c) Desire to eat.
4. Discussion
This study was conducted to evaluate whether consuming low-carb rice cooked in
a carb-reducing rice cooker affects blood glucose response. In addition, we investigated
the difference in sensory, hunger, fullness characteristics, and the DTE between low-carb
and regular rice. Our results showed that the iAUC of blood glucose was significantly
reduced at 15 and 30 min after low-carb WR intake compared to regular WR. Sensory
characteristics, and hunger, fullness, and DTE 3 h after eating values showed no difference
between low-carb rice and regular rice.
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Using a carb-reducing rice cooker produced ~20% fewer calories and carbohydrate
contents than those of the regular rice cooking method. Moisture content is a determinant
of the taste of rice, and the optimal amount of water for delicious rice is 1.2 to 1.3 times [26].
Several carb-reducing rice cookers on the market promote various starch-reducing effects,
such as 20–40%, but the cooking method for regular and low-carb rice is not standardized
and has not yet been compared. In this study, regular rice was cooked in water that was
1.2 times the weight of the rice according to the recipe for rice consumed in daily life, while
low-carb rice was cooked in water at 4 times the weight of rice. This method produced the
best taste and was used for the experiments.
Low-carbohydrate diets, which have recently attracted much attention, are effective
in weight loss and the prevention of chronic diseases such as diabetes by regulating the
glucose–insulin axis [27]. In women with gestational diabetes, or overweight or obese
adults, low-carbohydrate mixed meals had significantly reduced iAUC in blood glucose
and/or insulin [27,28]. In addition, the intake of a low-carbohydrate ketogenic diet for
12 weeks had an effect in reducing body weight and BMI [29]. Gene expression involved
in nutrient metabolism is also different during day and night and depends on meal composition [30]. Therefore, manipulating the meal type at night (e.g., more protein and less
carbohydrate) may mitigate the regulation of glucose uptake, and fatty acid synthesis and
oxidation [30]. Previous studies mainly evaluated the effect of a low-carbohydrate diet
with increased protein and fat content. This study evaluated the blood glucose response
in low-carb rice intake. The effect of reducing the blood glucose levels of low-carb rice
suggests that the blood glucose can be controlled, not through a high-protein or -fat meal,
and through daily meals.
WR is among the most important staple foods for the global population [1,2]. Asian
people consume cooked rice with almost every meal. The consumption of WR mainly
composed of starch can be a burden for people with diabetes and impaired glucose tolerance
who need to control their blood glucose [5,6]. Reducing the burden of blood glucose increase
in the intake of WR (high-GI and frequently consumed food) could reduce the stress of
diet control in people who need to control their blood glucose, and suggests the possibility
of blood glucose control through daily meal intake [7,8]. From the results of the study,
iAUC at 15 and 30 min after the consumption of low-carb WR was significantly lower
than that of regular WR. Delaying the increase in blood glucose is beneficial for blood
glucose management and can help in lowering postprandial blood glucose spikes, resulting
in stable blood glucose levels [31]. Therefore, these results show the positive effects of
low-carb WR against postprandial spikes in blood glucose, and suggest options for those
who hesitate to consume white rice due to the burden of blood glucose control.
The postprandial glucose response to carbohydrate meals is not only determined by
the amount of available carbohydrate, but also by fat, protein, and various nutrients [32,33].
Soluble dietary fiber in foods also influences the glycemic response after a meal [32,33]. The
consumption of intact grains containing at least 4 g of β-glucan and 30–80 g of available
carbohydrate is reportedly required to reduce postprandial blood glucose [34]. In addition,
studies reporting on the postprandial blood glucose reduction effect of ingesting barley
and brown rice also confirmed the effect of ingestion of 100% barley and 100% brown
rice, and not mixed grains with WR [35,36]. A previous study reported that MR with a
ratio of less than 30% is the most preferrable [37]. In another study, rice with a ratio of
mixed grains was 40% higher than rice with a ratio of 50% [38]. Therefore, in this study,
the ratio of mixed grains was selected as 40% for mixed rice that people can eat deliciously
by reflecting their preferences. The mixed grains used in this study were a mixture of
glutinous, brown, glutinous brown, black glutinous brown, red–brown, green–brown,
red–brown, compressed, sticky barley, and millet rice. The MR provided to the subjects in
the study was cooked by mixing 40% mixed grains and 60% WR, a commonly consumed
mixed rice recipe in Korea. Our results showed that the intake of MR with a mixed-grain
ratio of 40% did not affect postprandial blood glucose levels. We assumed that, since there
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was only 60% of WR in the MR, further reduction in blood glucose of the low-carb MR
could not be not easily attained.
To comply with diabetic diets, a major determinant of the effect of the diet on blood
glucose management, foods that are not palliative hinder sustaining it for a long period.
Low-carb rice in this study had about 20% fewer calories and less carbohydrate than
regular rice did (regular WR: 140.9 kcal; low-carb WR: 120.8 kcal; regular MR: 154.4 kcal;
low-carb MR: 129.3 kcal), but there was no noticeable difference in the sensory evaluation
(appearance, flavor, taste, texture properties, preference) and the feeling of hunger, fullness,
and DTE in consumption. When people are on a low-carbohydrate diet and consume
less rice, fullness is normally low, and hunger and DTE are high, and the diet is usually
accompanied by additional food intake, which leaves a low-carb diet with no health benefits.
However, results of our study show that maintaining a low-carb diet with a carb-reducing
rice cooker seems feasible because eating low-carb rice did not affect hunger or appetite.
Visual cues for food can affect food intake [39,40]. In this study, when low-carb rice
of equivalent weight (low-carb WR (EW); low-carb MR (EW), and low-carb rice) with
the same carbohydrate amount (low-carb WR (EC); low-carb MR (EC) was served with
regular rice (regular WR; regular MR), even when their weight differed by up to 30 g
(about 1–1.5 spoon), the difference was not noticeable with the naked eye. This may have
affected the feeling of satiety, as subjects visually perceived a similar amount of rice. When
regular WR (147 g, 50.0 g carbohydrate, 219.0 kcal) and low-carb WR (EW) (147 g, 40.6 g
carbohydrate, 177.6 kcal) were consumed, there was no difference in the feeling of hunger,
fullness, and urge to eat for 3 h after eating. These results suggest that consuming low-carb
rice (eventually lower calories with no significant empty feeling) can be used as dietary
therapy for body-weight loss.
The flavor of low-carb rice is closely related to the sustainability of low-carb rice
consumption in daily life. Even if there are foods that help in controlling blood glucose
due to their low-carb content, it is difficult to maintain intake if they do not taste good.
Therefore, low-carb rice does not exhibit sensory difference, such as regarding appearance,
flavor, taste, texture properties, and preference, compared to regular rice.
Common cooking principles of the carb-reducing rice cooker are as follows. First, put
rice and excess water (about four times or more the weight of rice) in a rice cooker and boil
them together. Next, after the starch in the rice had dissolved in the water, leaving only
an appropriate amount of water, rice is cooked after removing the extra water. When the
carb-reducing rice cooker was first released, it was mainly a wash-down type carb-reducing
rice cooker that drained water to the bottom. In this rice cooker, soft- or liquid-type rice was
prepared by exposing the rice to the water at the bottom. The siphon-type carb-reducing
rice cooker, which was released later, removes rice water with the upper tray and cooks the
rice. However, because of the cooking principle for reducing starch in the carb-reducing
rice cooker, starch in the rice is removed using water, and low-carb rice can be cooked with
a lot of water.
Some limitations of this study should be noted. First, no difference in blood glucose
response was found between regular and low-carb mixed rice. Second, the blood glucose
response test was not performed 180 min after eating to see how long the effect can last.
Third, the study was performed using the finger-prick blood test for convenience, but we
thus could not assess insulin hormone concentrations for more accurately assessing the
glycemic response.
The strengths of the study are as follows. First, this is the first study to evaluate and
publish the blood glucose response of low-carb rice cooked with a carb-reducing rice cooker.
Second, we found a way to control blood glucose with low-carb rice using WR, the staple
food of Asian countries. Third, there was no difference in the feeling of fullness, hunger,
and DTE between the consumption of low-calorie low-carb WR and regular rice.
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5. Conclusions
The study is the first clinical trial to evaluate the glycemic response effect of low-carb
rice cooked in a carb-reducing rice cooker. Low-carb and regular rice used in the study
was cooked with a recipe that could produce the optimal flavor, and the low-carb rice had
about 20% fewer calories and less carbohydrate than those of regular rice. Low-carb rice
had no difference in sensory characteristics, fullness, hunger, and DTE compared to regular
rice. These results indicate the health benefit of low-carb WR on postprandial spikes in
blood glucose levels. The possibility of low-carb rice as a substitute for regular rice can be
carefully claimed. Eating less carbohydrate (20% less carbohydrate and kcal per each meal
can add up to 35 g carbohydrate and 150 kcal deficit per day) without feeling deprived
contributes to improving the quality of life of people who need blood glucose control, such
as patients with diabetes or impaired glucose tolerance.
Author Contributions: Conceptualization, H.A., H.A.C. and Y.K.P.; methodology, H.A., M.L., H.A.C.
and Y.K.P.; formal analysis, H.A. and M.L.; investigation, H.A. and Y.K.P.; writing—original draft
preparation, H.A. and M.L.; writing—review and editing, H.A., H.A.C. and Y.K.P.; supervision,
H.A.C. and Y.K.P.; project administration, H.S. and Y.K.P.; funding acquisition, H.S. All authors have
read and agreed to the published version of the manuscript.
Funding: This work was supported by Korea Institute for Advancement of Technology (KIAT) grant
funded by the Korea Government (MOTIE) (P0014276, Industry Innovation Foundation Building
Program) and BK21 plus program AgeTech-Service Convergence Major through the National Research
Foundation (NRF) funded by the Ministry of Education of Korea (5120200313836).
Institutional Review Board Statement: The study was conducted in accordance with the Declaration
of Helsinki, and the protocol was approved by the Ethics Committee of the Institutional Review
Board (IRBs) of Kyung Hee University in September 2021 (no. KHGIRB-21-420).
Informed Consent Statement: All subjects gave their informed consent to participate in the study
before starting.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
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