Asia Pac J Clin Nutr 2017;26(3):421-426

421

Original Article

Eating glutinous brown rice for one day improves
glycemic control in Japanese patients with type 2
diabetes assessed by continuous glucose monitoring
Yuko Terashima RD, Yoshio Nagai MD, Hiroyuki Kato MD, Akio Ohta MD,
Yasushi Tanaka MD
Division of Metabolism and Endocrinology, Department of Internal Medicine, St. Marianna University
School of Medicine, Kanagawa, Japan
Background and Objectives: We investigated whether intake of non-glutinous brown rice (BR) or glutinous
brown rice (GBR) for 1 day had an influence on the daily glucose profile measured by continuous glucose monitoring (CGM) when compared with intake of non-glutinous white rice (WR). Methods and Study Design: A total of 37 inpatients with type 2 diabetes mellitus (T2DM) were recruited for a 3-day randomized triple cross-overtrial in which they ate WR, BR, or GBR for 1 day each. One of the three types of rice was eaten at breakfast,
lunch, and dinner on the first day, before switching to the other types on the second and third days. Each meal had
the same energy content and the same side dishes. The main outcome measures were the blood glucose profile determined by continuous glucose monitoring (CGM) and the profile of serum C-peptide (CPR) for 3 hours after
breakfast. A self-administered questionnaire was used to assess the palatability of each type of rice. Results: According to the CGM data, the mean 24-hour glucose concentration was lowest with GBR (p<0.01). Serum Cpeptide showed no significant differences among the three diets. Regarding palatability, BR was assigned significantly lower scores than WR and GBR (p<0.05), while there was no difference between WR and GBR. Conclusions: GBR intake suppressed the whole-day glucose profile of patients with T2DM, mainly by reducing postprandial glucose excursion, and GBR was preferred over BR with respect to palatability. GBR may be worth adding to the diet of patients with T2DM.

Key Words: type 2 diabetes, diet, continuous glucose monitoring, glutinous brown rice, postprandial hyperglycemia

INTRODUCTION
The objectives of treating type 2 diabetes mellitus (T2DM)
are to maintain or improve the quality of life and to prevent the development of diabetic complications throughgood glycemic control. To achieve these objectives, lifestyle modification (diet and exercise) is essential with orwithout pharmacotherapy. Regarding diet, most patientsare instructed to obtain 50-60% of their total energy requirement from carbohydrates.1 In the Asian region, rice
is a major source of carbohydrates, and Japanese tend toprefer white rice to brown rice with respect to taste andpalatability. However, white rice contains less dietaryfiber and trace elements (such as K, Mg, or Mn) thanbrown rice because these are mainly found in the bran,
which influences insulin secretion and/or insulin sensitivity.2 Thus, intake of white rice may be disadvantageous
for prevention or treatment of diabetes when comparedwith brown rice.
A recent cohort study of 60,000 Japanese persons
demonstrated that the risk of T2DM increases along with
the increase in the intake of white rice.3 The authors suggested that white rice with its lower content of dietaryfiber is rapidly absorbed from the intestine, leading topostprandial hyperglycemia that may be associated with ahigher incidence of diabetes. Conversely, Aune et al re-ported that replacement of refined grains, including riceand other cereals, with whole grains may reduce the riskof T2DM based on a meta-analysis of 16 prospective cohort studies.4 Similarly, the epidemiological analysis of
Hu et al showed that the risk of T2DM could be reducedby 16% if daily intake of 50 g of white rice was replacedwith brown rice having the same energy content.5 Thus,
the usefulness of brown rice or whole grain cereal for
prevention of T2DM has been suggested by epidemiological studies, but the direct effect of these grains on the
glucose profile has not been fully investigated. Accordingly, it is important to evaluate the effect of brown riceon postprandial glucose excursion compared with white
rice in T2DM patients.
Japanese tend to prefer white rice over brown rice because brown rice is drier due to inclusion of bran. Rice
Corresponding Author: Dr Yoshio Nagai, Division of Metabolism and Endocrinology, Department of Internal Medicine, St.
Marianna University School of Medicine, 2-16-1, Sugao,
Miyamae-ku, Kawasaki, Kanagawa 216-8511, Japan.
Tel: +81-44-977-8111; Fax: +81-44-976-8516
Email: ynagai@marianna-u.ac.jp
Manuscript received 28 November 2015. Initial review completed and accepted 17 December 2015.
doi: 10.6133/apjcn.042016.07

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Y Terashima, Y Nagai, H Kato, A Ohta and Y Tanaka

can be classified into glutinous and non-glutinous types.
In Japan, the former type is mainly used in rice cakes,
while the latter is generally boiled and eaten with daily
meals. The starch in glutinous rice is 100% amylopectin,
while non-glutinous rice has starch consisting of 80%
amylopectin and 20% amylose, and the stickiness of glutinous rice is based on this difference in the compositionof starch. Because glutinous brown rice is not drier andtastes good despite containing bran, a frozen boiled glutinous brown rice product is already being marketed commercially in Japan. In the present study, we aimed to verify whether intake of non-glutinous brown rice (BR) or
glutinous brown rice (GBR) for one day could improvethe daily glucose profile measured by continuous glucose
monitoring (CGM) compared with that after intake of
non-glutinous white rice (WR). In addition, we compared
the taste and texture of BR and GBR with WR by performing a questionnaire survey.
MATERIALS AND METHODS
Participants
Thirty-seven Japanese patients with T2DM were recruitedfrom the inpatient diabetes unit of St. Marianna University Hospital (Kawasaki, Japan). They had been admitted
for treatment of diabetes, and fasting blood glucose wasmaintained at <140 mg/dL by diet with or without oral
hypoglycemic agents and/or insulin. Patients with cancer,
anemia, renal failure, chronic liver disease, thyroid disease, or pregnancy were excluded. Physical activity was
not restricted, but was voluntarily limited by the subjects
to quiet activities (such as reading or watching television).
This study was conducted in accordance with the ethicalprinciples of the Declaration of Helsinki, and was approved by the ethics committee of St. Marianna University School of Medicine (No. 2242). All patients gave written informed consent prior to participation.
Dietary intervention
The study was performed according to a cross-over andcounterbalanced design involving six possible orders oftreatment. Patients were studied on three consecutive
days; they ate WR, BR, or GBR on 1 day each, while theother dishes of each meal were unchanged throughout the
study. They were randomly allocated to six groups, depending on the order of eating the three types of rice [WRon the first day, BR on the second day, and GBR on thethird day (WR/BR/GBR), WR/GBR/BR, BR/WR/GBR,
BR/GBR/WR, GBR/WR/BR, and GBR/BR/WR]. Test
meals were eaten three times a day (breakfast, lunch, anddinner), and each meal consisted of a staple food (WR,BR, or GBR) and side dishes. Patients selected their preference from among 4 side dishes (omelet, hamburger,
white fish fillet, or salmon) for breakfast, lunch, or dinner.
After selecting a side dish, the patient ate the same dish at
the same meal every day for three days, and only the staple food was changed. The total energy and nutrition intake was equivalent for all types of meal (26.5±1.7kcal/kg of ideal body weight). There were no subjects
who had previously been eating brown rice on a daily
basis.

Clinical measurements
Anthropometric measurements such as height and weight
were obtained for all participants using standardized
techniques, and BMI was calculated. Venous blood samples were collected at 0, 30, 60, 120, and 180 min after
breakfast for measurement of plasma glucose, serum Cpeptide, and plasma lipids [triglycerides (TG), total cholesterol (TC), and free fatty acids (FFA)]. The plasma
glucose concentration was measured by the hexokinase
UV method and serum C-peptide was determined by the
CLEIA method. Plasma lipids were determined by enzymatic methods. Results were expressed as themean±standard deviation (M±SD).
CGM protocol
Continuous glucose monitoring (CGM) system (iProTM2;
Medtronic, Northridge CA, USA) was used to measuresubcutaneous interstitial glucose concentrations on an
ambulatory basis for 72 consecutive hours. The sensor
was inserted on day 0 and was removed in the midmorning on day 4. All of the patients also performed selfmeasurement of blood glucose (SMBG) at least 4 times
daily using a blood glucose monitor (OneTouch Ultra;
Life scan, Milpitas, CA, USA), and input the data into the
CGM recorder for calibration. They were instructed tocalibrate the system at least 2 h after meals. The average
glucose value was recorded every 5 mins, resulting in 288
measurements in 24 h. To evaluate the effect of the typeof rice on daily glucose excursion, CGM data obtained
from the start of breakfast to just before breakfast on thenext morning were used to calculate the 24 hour mean
glucose concentration, its standard deviation (SD), andthe mean amplitude of glucose excursion. In addition, theincremental area under the glucose curve for 3 hours(IAUC-G3h) after the start of each meal was calculated atbreakfast, lunch, and dinner on each day. Results wereexpressed as the mean±SD.
Food palatability questionnaire
To assess the palatability of WR, BR, and GBR, a selfadministered questionnaire was completed after dinner oneach day. The questionnaire consisted of the following
five items: taste (delicious or not), texture (rice cake-likeor dry), consumability (can be eaten every day or not),habitual intake (possible to consume for one meal every
day or not), and satiety (feeling of fullness or not). Each
item was assigned a score, which could range from themost positive response (+3 points) to the most negative
response (-3 points).
Statistical analysis
Results were expressed as the mean±SD. One-way
ANOVA followed by a multiple comparison test (Bonferroni’s method) was used to compare the effects of WR,
BR, and GBR. All analyses were performed using ExcelToukei 2012 (Social Survey Research Information Co.,
Ltd.). Differences were considered to be significant if theprobability value (p) was less than 0.05.
RESULTS
Characteristics of the subjects
Among the 37 subjects registered in the present study, 7

Glutinous brown rice and glucose profile

Table 1. Subjects characteristics
Characteristicn (men/women)
Age (years)
BMI (kg/m2)
Obese (BMI ≥25 kg/m2), [% (n)]HbA1c (%)
Fasting serum C-peptide (ng/mL)
Diabetes treatment, [% (n)]DietOral hypoglycemic agent
Insulin (plus oral hypoglycemic agent)
Glucagon like peptide-1 receptor agonist(including oral hypoglycemic agent)

17/13
61.1±12.526.3±3.9
73.3 (22)8.7±1.4
1.4±0.9
16.7 (5)13.3 (4)66.7 (20)
3.3 (1)423

types of rice (35.6±14.6 mg/dL and 58.0±21.3 mg/dL,
respectively, with WR; 37.6±15.9 and 61.6±23.5, respectively, with BR; and 33.2±13.2 and 57.1±21.5, respectively, with GBR). As shown in Table 2, the IAUC-G3h after
lunch and the total IAUC-G3h across three meals weresignificantly lower with GBR than WR, but there were no
significant differences for these parameters between BR
and WR (25391±6824 [(mg/dL)·min] and 83812±17601[(mg/dL)·min], respectively, with GBR; 29418±9430 and
90373±24121, respectively, with BR; and 30740±7262
and 93306±21427, respectively, with WR). We also assessed the glucose profile according to each treatment andfound it to be similar regardless of the treatment group(Supplemental figure 1).

Data are the mean±SD or n.

were excluded from analysis because they required emergency treatment (n=2) or because of insufficient glucose
data due to CGM problems (n=5). Table 1 displays theclinical characteristic of the remaining 30 subjects. The
baseline age was 61.1±12.5 years, BMI was 26.3±3.9kg/m2, HbA1c was 8.7±1.4% and fasting C-peptide was
0.4±0.9 ng/mL. Regarding the treatment of diabetes, 5patients were on diet alone, 4 were also taking oral medications, 20 were also using insulin, and 1 subject was also
taking lixisenatide (a glucagon like peptide-1 receptor
agonist).
Plasma glucose and serum CPR in the first 180 minutes
after breakfast
After breakfast, the area under the plasma glucose concentration vs. time curve (AUC-PG) and the AUC of serum C-peptide (AUC-CP) were not significantly different
among the three types of rice (9036±6254 [(mg/dL)·min]and 437±347 [(mg/dL)·min], respectively, with WR;
8897±6113 and 348±269, respectively, with BR; and7317±5596 and 456±626, respectively, with GBR). The
concentrations of plasma lipids (TG, TC, and FFA) also
showed no significant differences among the 3 types ofrice after breakfast.
Circadian variation of blood glucose detected by CGM
Figure 1A displays the whole-day glucose profile when
the patients ate each type of rice as determined by CGM.
As shown in Figure 1B, the 24-hour mean glucose concentration was significantly lower when the patients ate
GBR (126.3±22.0 mg/dL) than when they ate WR(144.2±28.5), while there was no significant difference
from WR with BR (137.2±29.8). However, there were no
significant differences of the 24-hour glucose SD andmean amplitude of glucose excursion among the three

Palatability of the 3 types of rice
The results of the questionnaire for the 3 types of rice areshown in Figure 2 (taste, texture, consumability, habitual
intake, and satiety). The total score of BR was significantly lower than those of WR and GBR (3.4±5.3 for BR,
6.5±5.9 for WR, and 6.7±3.6 for GBR; p<0.05), while
there was no significant difference between WR and GBR.
Regarding the individual items, BR received significantly
lower scores for taste and texture than GBR (p<0.05 and
p<0.01, respectively), and BR also received a significantly lower consumability score than WR (p<0.05).
DISCUSSION
There were three main findings of the present study. First,
the AUC-PG and AUC-CP over 3 hours after the start ofbreakfast showed no significant differences following
intake of the three types of rice. Second, the 24-hourmean glucose concentration and the total IAUC-G3h
across three meals were significantly lower with GBR
than WR, while there were no significant differences between BR and WR. Third, the palatability of GBR was
similar to that of WR.
In this study, the effect of GBR could not be detectedby intermittent measurement of plasma glucose after
breakfast, but was revealed by detailed assessment of thewhole-day glucose profile using CGM. While BR did not
improve glucose excursion compared with WR in thepresent study and its palatability was inferior to that ofWR, intake of GBR ameliorated both postprandial andwhole-day glucose excursion (Figure 1A). In addition, thesubjects considered that the palatability of GBR was better than that of BR and similar to WR. Previous studies
have demonstrated that increasing dietary fiber intake
improves glycemic control due to suppression of the peak
postprandial blood glucose concentration.6,7 Mohan et alcompared the effect of WR, BR, and BR with legumes on

Table 2. Three-hours postprandial AUC with each type of rice
Breakfast
Lunch
DinnerTotal(mg/dL) · min(mg/dL) · min(mg/dL) · min(mg/dL) · minWR31645±8000
30740±7262
30921±8639
93306±21427

BR31446±8996
29418±9430
29508±8981
90373±24121

WR: white rice; BR: brown rice, GBR: glutinous brown rice.
Data are the mean±SD
Difference vs WR according to multiple comparison by Bonferroni’s test **; p<0.01.

GBR29465±6277
25391±6824**
28956±7890
83812±17601**

p value
0.073
0.000
0.208
0.001

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Y Terashima, Y Nagai, H Kato, A Ohta and Y Tanaka

Breakfast

Lunch

Dinner

BR

WR

GBR

Time
Figure 1A. Average glucose concentration profile over 24 hours determined by continuous glucose monitoring in patients with T2DM fed
white rice (WR), brown rice (BR), or glutinous brown rice (GBR). Data are expressed as the mean±SD (N=30). Dotted lines show thestart glucose of eating breakfast, lunch, and dinner.

( mg/dL )****Figure 1B. Comparison of the 24-hour mean glucose concentration determined by continuous monitoring in patients with T2DM fed
white rice (WR), brown rice (BR), or glutinous brown rice (GBR). Data are expressed as the mean±SD (N=30). **p<0.01 by multiple
comparison with Bonferroni’s test.

postprandial glucose.8 Their subjects who ate BR and BR
with legumes groups, which are rich in dietary fiber, had
lower peak postprandial glucose concentrations comparedwith those who ate WR. In the present study, the average
daily intake of dietary fiber was 12.7 g with the WR meal,
22.0 g with the BR meal, and 23.3 g with the GBR meal,so dietary fiber intake was much higher with BR and
GBR. However, the increment of glucose from just before
a meal to the postprandial peak was similar among the 3
meal types when assessed by CGM (Figure 1A). On theother hand, the postprandial decline of glucose from peak
to trough was largest with GBR. Thus, the mechanism
underlying postprandial suppression of glucose concentrations by GBR was unrelated to dietary fiber. Since intake of refined glutinous rice has been reported to increase postprandial glucose concentrations compared with
WR,9 the difference of starch between glutinous and nonglutinous rice also fails to explain the glucose-lowering
effect of GBR.
We measured intrinsic insulin secretion in the morning
after breakfast and found no difference of AUC-CP

among the three types of rice, but we did not assesswhole-day insulin secretion. Accordingly, the precise
effect of GBR or BR on insulin secretion compared with
WR is not clear. Regarding this issue, Shimabukuro et alreported that intake of BR for 8 weeks improved HOMAIR and reduced visceral fat in subjects with metabolic
syndrome.10 In addition, Weickert et al found that evenshort-term intake of a fiber-rich cereal diet for only 3days could improve insulin resistance as assessed byeuglycemic-hyperinsulinemic clamp.11 However, the effect of GBR on insulin sensitivity has not been evaluatedbefore. The bran of BR is enriched in trace elements, vitamins, and polyphenols, and some of the components ofbran (such as K, Mg, Mn, and thiamine) are known to
influence insulin secretion or insulin sensitivity.2,12 We
did not analyze the bran of BR and GBR in this study, but
comparison of these brans and evaluation of their effecton insulin secretion/insulin sensitivity needs to be done in
the future to provide clues to the mechanism underlying
the effect of GBR.
To precisely assess the palatability of each type of rice,Glutinous brown rice and glucose profile

425(Score)

†

†

††

*

Figure 2. Palatability of white rice (WR), brown rice (BR), and glutinous brown rice (GBR) results of a questionnaire covering 5 items(taste, texture, habitual intake, consumability, and satiety) using a bipolar 7-point ordinal scale ranging from -3 to +3. The scores for each
item and the total score are shown. Data are expressed as the mean±SD (N=30). *p<0.05 vs WR and †p<0.05, †† p<0.01 vs GBR by multiple comparison with Bonferroni’s test.

a blinded design would have been desirable, but we employed an open label cross-over design in the present
study because of the difficulty of blinding the different
types of rice. Accordingly, we could not exclude the possibility of bias, and lack of familiarity with the taste or
texture of GBR might also have influenced the palatability scores assigned by the patients. On the other hand, thehabitual intake and satiety scores were similar among thethree types of rice. There were striking differences oftaste, texture, and consumability between BR and GBR in
spite of their similar appearance. Thus, GBR appeared toovercome the problem of poor palatability associated withBR.
There were some limitations of the present study. First,
the number of patients was small and the study period
was only one day for each meal. Second, the whole-day
glucose profile was determined by CGM rather than byblood sampling. Third, we did not assess either insulin
sensitivity or whole-day intrinsic insulin secretion. Thus,
further research into the mechanism underlying the effectof GBR and a longer clinical study in a larger patient
population are required for confirmation of our findings.
In conclusion, one-day intake of GBR suppressed thewhole-day glucose profile in patients with T2DM, mainly
by modifying postprandial glucose excursion, and GBR
was preferred over BR with respect to palatability. It may
be worth adding GBR to the diet of patients with T2DM.
ACKNOWLEDGEMENTS
We appreciate the cooperation of all the physicians in the team
who gave their time for this study.
AUTHOR DISCLOSURES
None of the authors have any conflicts of interest associatedwith this study. This work was partly funded by a grant from the
Yazuya Food and Health Research Center.

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Supplemental figure 1: Average glucose concentration profile over 24 hours determined by continuous glucose monitoring in patientswith T2DM treated with intensive insulin treatment (N=17), drug naïve (N=5), oral hypoglycemic agents only (N=4), basal supported
oral therapt (N=2), or GLP-1 receptor agonist (N=1), biphasic insulin aspart 30/70 (N=1).