Glycative Stress Research
Online edition : ISSN 2188-3610
Print edition : ISSN 2188-3602
Received : August 6, 2020
Accepted : August 27, 2020
Published online : September 30, 2020
doi:10.24659/gsr.7. 3_220

Original article

The effects of food materials on postprandial hyperglycemia
Shiori Uenaka 1), Masayuki Yagi 1), Wakako Takabe 1, 2), Yoshikazu Yonei 1)
1) Anti-Aging Medical Research Center/Glycative Stress Research Center, Graduate School of Life and Medical Sciences,
Doshisha University, Kyoto, Japan
2) Department of Materials and Life Science, Faculty of Science and Technology, Shizuoka Institute of Science and Technology,
Shizuoka, Japan

Abstarct

Purpose: One of the methods for reducing glycative stress is suppression of postprandial hyperglycemia (PPHG). In thisstudy, we picked up food materials with nutrition, i.e., protein, lipids, acetic acid, and dietary fiber, which were reported tohave the suppressing effect on PPHG, and their effects were verified.
Methods: The subjects were 20 healthy young men and women (8 men, 12 women, 23.3 ± 1.8 years). As the standard
food, 200 g of cooked rice (carbohydrate: 67.8 g) + 2.5 g of seasoning was used. The model food, rich in specific nutrition,
included A: Salad chicken (protein: low dose (L) 11. 5 g/ high dose (H) 23.0 g), B: olive oil (lipid: 14 g/28 g), C: grain vinegar(acetic acid: 0.63 g/1.26 g), D: indigestible dextrin (dietary fiber: 4.2 g/8.4 g), and E: cabbage (dietary fiber: 0.9 g/1.8 g). The
complex foods include F: vinegar rice, G: fried chicken, H: fried chicken + lemon juice, and I: Japanese dumplings (gyoza)+ ponzu soy sauce. The test food was ingested for 10 min after starting the test, and in the cases of rice + the model food orrice + complex food, these were ingested prior to rice. FreeStyle Libre Pro (Abbott) was used to continuously measure blood
glucose levels in the tissue interstitial fluid. The effect on PPHG was evaluated by the maximum blood glucose change (ΔCmax)
and the incremental area under the curve (iAUC). This study was approved by the Ethics Review Committee of Doshisha
University.
Results: When the model foods A, B, C, and E were ingested in high doses (H), the iAUC tended to be lower than that of thestandard food. In particular, the ΔCmax and iAUC in test food C were significantly decreased (p < 0.05) and the effect wasin a dose dependent manner. On the other hand, the model food D did not have a suppressing effect on PPHG. As comparedto the standard food, the complex food F tended to lower ΔCmax and iAUC, while the complex foods G, H, and I significantly
reduced the ΔCmax and iAUC (p < 0.05).
Conclusion: The suppression of PPHG was strongly influenced by protein and acetic acid in food, and weakly influenced
by lipids and dietary fiber in the young subjects. It was suggested that the content of protein and acetic acid in complex foods
may be important when expecting side dishes to suppress PPHG.

KEY WORDS: postprandial hyperglycemia, protein, lipids, acetic acid, dietary fiber

Introduction
In the body, reducing sugars, i.e. glucose, bind to proteins
non-enzymatically, and glycation end products (AGEs),
which are the causative factors of aging, are produced andaccumulated; these reactions are called “glycative stress”,.
Glycative stress is one of the risk factors for aging and is afactor that promotes skin aging and diabetic complications 1, 2).
Methods for reducing glycative stress include suppression of

postprandial hyperglycemia (PPHG), recently referred to as“glucose spikes”, suppression of AGE formation, and promotionof AGE decomposition/excretion. Among these, suppressionof PPHG is a measure that can be easily incorporated into adaily diet.
Methods to reduce PPHG include reduction of sugar
intake (sugar restriction) 3), intake of low glycemic index (GI)
foods 4), intake of specified health foods, i.e., indigestible
dextrin 5), Salacia 6, 7), and eating vegetables first 8, 9). However,Contact Address: Professor Masayuki Yagi, PhD
Anti-Aging Medical Research Center/Glycative Stress Research Center,
Graduate School of Life and Medical Sciences, Doshisha University
1- 3, Tatara Miyakodani, Kyotanabe, Kyoto, 610-0394 Japan
TEL / FAX: +81-774 -65- 6394 e-mail: myagi@mail.doshisha.ac.jp
Co-authors: Uenaka S, ctud2025@mail4.doshisha.ac.jp;
Takabe W, takabe.wakako@sist.ac.jp; Yonei Y, yyonei@mail.doshisha.ac.jp_ 22 0 _Glycative Stress Research 2020; 7 ( 3) : 220-231(c) Society for Glycative Stress ResearchGlycative Stress Research

the dietary method of eating low GI foods or vegetables firstsometimes reduces mental enjoyment due to mental stress onappetite. On the other hand, continuous intake of foods for
specified health foods as a daily diet poses a cost problem.
It was already shown that ingestion of beef bowl was
effective in suppressing PPHG, and that its action was
suggested to be due to the meat containing protein and lipids
10, 11). The pre-meal intake of lemon juice was reported tohave a suppressing effect of PPHG, and the action was due tocitric acid and polyphenol contained in lemon juice 12). Also
the pre-meal intake of vinegar 13) suppressed blood glucose
elevation, and this action was possibly due to the acetic
acid contained in vinegar. Since general food is a complex
combination of various materials and nutritional ingredients,
it is difficult to estimate how much food intake affects theincrease in postprandial glucose level.
Based on these things, the purpose of this study was tocompare and evaluate the effects of nutritional components
on PPHG by co-eating various foods rich in protein, lipid,
acetic acid, and dietary fibers. By studying the effect ofeach nutritional component on blood glucose, this study
was designed so that we can propose a method for reducing
glycative stress from the daily diet menu in a different way
from dietary restrictions.

Methods
Subjects
There were 20 subjects who met the following selection
criteria ( Table 1 ). Men and women between the ages of 20
and 29 at the time of obtaining consent to participate in
the study. Study participants were healthy persons without

chronic illness. Persons with the ability to give consent after
receiving an adequate explanation of the purpose and content
of the study, and who volunteered to participate of theirown accord after proper understanding and who provided
a written consent to participate in this study. Persons who
can attend the designated examination date to undergo
examination. Persons determined to be suitable as a subjectof this study by the principal investigator.

Survey items and inspection contents
As a subject background survey, the subjects themselvescompleted a blood test along with filling out a questionnaire
regarding their age, medical history, and food allergies (Table2). For the test, FreeStyle Libre Pro (Abbott Laboratories,
Chicago, USA) was used, and the glucose concentration in
the interstitial fluid measured during the test period was usedas the blood glucose level 14).

Test protocol
As in the previous reports 10-12), this study was conductedaccording to the uniform protocol by the Japan Glycemic
Index (GI) Study Group 15).
Subjects were instructed to observe the following
items during the test period. Avoid irregular life, i.e., sleep
deprivation, overeating, excessive drinking, and live as usual.
It is prohibited to start taking health foods or supplements.
Other than that, it is prohibited to affect the test results.
Instructions were given on the day before and on the
day of the test so that the following items were observed.
Excessive exercise is prohibited. Sleep 6 hours or more theday before the test. Alcohol drinking is prohibited from the
day before the test until the end of the test on the day of theTable 1. Subject profile.
Number of subjects
Age
Body height
Body weight
BMI

Unit

Total

Male

Total

years

20
23.3 ± 1.8824.3 ± 2.0

1222.6 ± 1.3

cm
kg

162.7 ± 9.3
57.0 ± 11.2
21.4 ± 2.4

170.4 ± 4.5
65.0 ± 12.1
22.3 ± 3.3

157.5 ± 7.9
51.7 ± 7.0

20.8 ± 1.4

Results are expressed as mean ± standard deviation. BMI, body mass index,

Table 2. Result of the blood chemistry test.
Test item

Unit

Measured value

Reference range

FBG
HbA1c
Insulin
Total cholesterolTG
HDL - CLDL - Cmg/dL

80.9 ± 6.0
5.3 ± 0. 2

70 - 109
4.6 - 6. 2

%

μU/mL
mg/dL
mg/dL
mg/dL
mg/dL

6. 2 ± 2.1
185.9 ± 33.9

1.7 - 10.4
120 - 219

105.7 ± 31. 3

65 - 139

83. 2 ± 45.9
63.9 ± 13. 5

30 - 14 9
4 0 - 85

Results are expressed as mean ± standard deviation. FBG, fasting blood glucose; TG, triglyceride; HDL-C, high-density
lipoprotein cholesterol; LDL-C; low-density lipoprotein cholesterol.

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Food Materials and Postprandial Hyperglycemia

test. For dinner on the day before the pretest and the test,
avoid high-lipid foods and do not ingest anything other thanwater after 22:00. On the day of the test, physical activity
that may cause exercise and sweating is prohibited until theend of the test. For women, the test is not conducted during
the menstrual period.
During the test, the subjects stayed in a sitting position
and were prohibited from making phone calls, sleeping,excessive brain activity, i.e., e-mail, computer, and physicalactivity.
Subjects self-attached the Libre Pro sensor to the outsideof the upper arm two days before the test. During the wearing
period of the sensor, no restrictions were placed on bathing,swimming, and exercise. During the test, the standard or test
food was ingested for 10 min at 10:00. Subjects then watcheda DVD in a sitting position, allowing them to remain relaxeduntil 12:00, when the test ended.
The standard and test foods were swallowed afterchewing 30 times or more. Blood glucose levels were
measured 15 min after starting the test food (1st time), 15

min after starting the test (2nd time), 30 min (3rd time), 45
min (4th time), 60 min (5th time), and 90 min (6th time) and
120 min (7th time).

Test food
The nutritional components of the test foods used in the
study were calculated using the values indicated on each food
( Table 3-5 ). Cooked (steamed) rice 200 g (Sato no Gohan
Koshihikari: Sato Foods, Niigata, Japan) + 2.5 g of seasoning(Noritama: Marumiya Food Industry, Suginami-ku, Tokyo,
Japan) was used as the standard food.
For the test foods, 5 model foods containing a large
amount of nutrition, which were reported to have an effect of
reducing PPHG, 4 complex foods containing some or all of
those nutrition, and cooked rice were used.
The model foods include A: Salad chicken (Awaji Island
Alga salt domestic salad chicken: Prima Ham, Shinagawa-ku,
Tokyo), B: Olive oil (Garcia extra virgin olive oil: Tominaga
Trading, Kobe, Hyogo, Japan), C: Grain vinegar (Mitsukan,

Table 3. Nutrition facts of test food (Standard food and model foods A-E).
Test foodStandard food
AL/AH

Serving unit(g)

Energy(Kcal)

Protein(g)

Lipids(g)

Acetic acid(g)

Carbohydrate(g)

Dietary fiber
(g)

200

294

4.2

0

0

67.8

60.6

255/310352 /410

15.7/ 27.2

0.95/1.9

uncalculated

68.5/69.2

0.65 / 0.7

0/0

0.63/1.26

68.9 / 70

0/0

BL/BH

214 /228
215/230

297.8/301.6

4.25/ 4.3

DL/DH

205.2 /210.4

298.9 to 301.5/
303.8 to 309

0/0

0/0

uncalculated

72.4 / 77

4.8 / 9EL/EH

250 / 300

306 / 318

4.9 /5.6

0/0

070.4 / 73

1.5/ 2.4

CL/CH

420/546

4.2 /4.2

14 / 28

0

0/0

0/0

Standard food; cooked rice 200 g, AL; salad chicken 55 g before cooked rice 200 g, AH; salad chicken 110 g before cooked rice 200 g, BL; olive oil 14 g before
cooked rice 200 g, BH; olive oil 28 g before cooked rice 200 g, CL; grain vinegar 15 g before cooked rice 200 g, CH; grain vinegar 30 g before cooked rice 200 g,
DL; indigestible dextrin 5.2 g before cooked rice 200 g, DH; indigestible dextrin 10.4 g before cooked rice 200 g, EL; cabbage 50g before cooked rice 200 g, EH;
cabbage 100g before cooked rice 200 g

Table 4. Nutrition facts of test food (Complex food F, I).
Test foodServing unit(g)

Energy(Kcal)

Protein(g)

Lipids(g)

Acetic acid(g)

Carbohydrate(g)

Dietary fiber
(g)

F

198

290.4

3.7

0

0.6

67.7

0.5

I

282

469.1

12.3

16.2

0.3

67.7

2.6

F, vinegared rice (cooked rice 177 g + sushi vinegar 21 g); I, Japanese dumplings (gyoza) 138 g + ponzu soy sauce 15 g before cooked rice 129 g

Table 5. Nutrition facts of test food (Complex food G, H).
Test foodServing unit(g)

Energy(Kcal)

Protein(g)

Lipids(g)

Citric acid(g)

Carbohydrate(g)

Dietary fiber
(g)

G

284

479.6

20.8

13.4

0

67.8

1. 5

H

295

478.7

20.7

13.4

1

G, fried chicken 135 g before cooked rice 14 9 g; H, fried chicken 135 g + lemon juice 15 g before cooked rice 145 g_ 222 _

67.8

1. 5

Glycative Stress Research

Handa, Aichi, Japan), D: Indigestible dextrin (Easy Fiber
Tokuho: Kobayashi Pharmaceutical, Chuo-ku, Osaka, Japan),and E: Cabbage (Salad Club shredded cabbage: Salad Club,
Chofu, Tokyo).
The complex foods include F: vinegared rice (Satono Gohan) assorted by sushi vinegar with kelp soup stock(Mitsukan), G: 4 pieces of fried chicken (Tokukara: Nichirei
Foods, Chuo-ku, Tokyo), H: 4 pieces of fried chicken(Tokukara) + lemon juice (Pokka lemon 100: Pokka Sapporo
Food & Beverage, Shibuya-ku, Tokyo), I: 6 pieces ofJapanese dumplings (gyoza) + ponzu soy sauce (Frozen
Gyoza: Ajinomoto, Chuo-ku, Tokyo, Ajipon: Mitsukan).
When the complex food was eaten together with rice, thetotal carbohydrate amount was adjusted to the standard food(rice 200 g, carbohydrates: 67.8 g).
· Standard food: rice 200 g + seasoning 2.5 g
· Test food AL (salad chicken low dose + cooked rice): Saladchicken 55 g + rice 200 g + seasoning 2.5 g
· Test meal AH (salad chicken high dose + cooked rice): Saladchicken 110 g + rice 200 g + seasoning 2.5 g
· Test food BL (low dose of olive oil + cooked rice): Olive oil
14 g + rice 200 g + seasoning 2.5 g
· Test food BH (high-dose olive oil + cooked rice): olive oil
28 g+ rice 200 g + seasoning 2.5 g
· Test meal CL (low-dose grain vinegar + cooked rice): Grainvinegar 15 g + rice 200 g + seasoning 2.5 g
· Test food CH (high-dose grain vinegar + cooked rice): Grainvinegar 30 g + rice 200 g + seasoning 2.5 g
· Test food DL (low-dose indigestible dextrin + cooked rice):
Indigestible dextrin 5.2 g + rice 200 g + seasoning 2.5 g
· Test food DH (high dose of indigestible dextrin + cookedrice): Indigestible dextrin 10.4 g + rice 200 g + seasoning
2.5 g
· Test food EL (low dose cabbage + cooked rice): cabbage 50 g
+ rice 200 g + seasoning 2.5 g
· Test food EH (high dose cabbage + cooked rice): cabbage
100 g + rice 200 g + seasoning 2.5 g
· Complex food F (vinegared rice): sushi vinegar 21 g + rice
177 g
· Complex food G: fried chicken 135g+ rice 149 g + seasoning
2.5 g
· Complex food H: fried chicken 135 g + lemon juice 15 g +rice 145 g + seasoning 2.5 g
· Complex food I: Gyoza 138 g + ponzu soy sauce 15 g + rice
129 g + 2.5 g seasoning
The standard and test foods were consumed 10 min after thestart of the test. When ingesting the model food or complex
food and the standard food, the model food or complex food
was ingested in the first 5 minutes, and then the standard
food was ingested. Grain vinegar and indigestible dextrin
were ingested after diluting them in 150 mL of water. The
complex food F (vinegared rice) was prepared by mixing
sushi vinegar with cooked rice and ingesting it 10 min after
the start.

Selection of subjects for efficacy analysis
Regarding the efficacy analysis, from the subjects whocompleted all the prescribed tests and contents of the trials,
subject to the following exclusion criteria were excluded.

A person whose behavior impairs the reliability of the test
results was remarkably observed. Persons who were found tohave met the exclusion criteria or were unable to comply withthe restrictions.
Since there were no subjects that met the exclusion
criteria, 20 participants were all included in the efficacy
analysis.

Statistical analysis
For the efficacy analysis, the below values were
measured in the selected subjects; change in blood glucose(Δ blood glucose; ΔBG) obtained by subtracting the value
before the test food was ingested (first time; 0 min value)
from the measured values after the test food was ingested,
the maximum value (ΔCmax) and incremental area undercurve (iAUC) according to the uniform protocol of the Japan
Glycemic Index (GI) Study Group.
IMB SPSS Statics 26 (IMB Japan, Tokyo, Japan)
was used for the statistical analysis. The paired-t test was
performed for comparison between two groups, while
Bonferroni test was used for multiple analyses, and it was
judged as a significant difference when the risk rate wasless than 5 % (p < 0.05) in a two-sided test. Results wereexpressed as the average value ± standard error (SE).

Ethical standards
This study was conducted in compliance with the
Declaration of Helsinki (revised at the 2013 WMA Fortaleza
General Assembly) and the ethical guidelines for humanbased medical research (notification by Ministry of
Education, Culture, Sports, Science and Technology [MEXT]
and Ministry of Health, Labour and Welfare [MHLW]). The
test content was fully explained to the subjects in advance.
The test was implemented after the applicant requested
participation in the test and received a voluntary consent
form. This study was conducted under the deliberation andapproval of the Ethics Review Committee of Doshisha
University (application No. 18039). This test was preregistered in the public database established by the National
University Hospital Meeting (UMIN Test ID: 000034009).

Results
Salad chicken intake and PPHG suppression
Out of 20 total subjects, 10 subjects (4 males, 6 females,23.3 ± 2.2 years, 161.8 ± 8.0 cm, 55.2 ± 11.2 kg, body massindex: BMI] 20.9 ± 2.6 kg/m 2) participated in the test. The
test food was salad chicken (A).
The change in ΔBG after starting the test is shown in
Fig. 1-a. No difference was observed in the fasting blood
glucose level (0 min). Blood glucose increased after ingestingeach test food, reached the maximum value after 45 min,and then decreased until 120 min later. There was slightdifference in the blood glucose level at each time among the
subjects, it was not significant. The average value of ΔBG ateach time was lower in the model foods AL and AH than in
the standard food, but it was not significant.

_ 223 _

Food Materials and Postprandial Hyperglycemia

Fig. 1. Fluctuation of the blood glucose level at the time of intaking test food ahead of rice.
a) AL and AH, b) BL and BH, c) CL and CH, d) DL and DH, e) EL and EH. Results are expressed as mean ± standard error, n = 10,† p < 0.1, * p < 0.05 vs standard food, Bonferroni test. Standard food, cooked rice 200 g; AL, salad chicken 55 g before cooked rice 200g; AH, salad chicken 110 g before cooked rice 200 g; BL, olive oil 14 g before cooked rice 200 g; BH, olive oil 28 g before cooked rice
200 g; CL, grain vinegar 15 g before cooked rice 200 g; CH; grain vinegar 30 g before cooked rice 200 g; DL, indigestible dextrin 5.2
g before cooked rice 200 g; DH, indigestible dextrin 10.4 g before cooked rice 200 g; EL, cabbage 50 g before cooked rice 200 g; EH,
cabbage 100g before cooked rice 200 g,_ 22 4 _Glycative Stress Research

ΔCmax was 62.7 ± 4.3 mg/dL for the standard food,54.2 ± 4.2 mg/dL for AL, 46.2 ± 5.7 mg/dL for AH, and nodifferences were observed (Fig. 2-a). The iAUC was standard
food: 4,690 ± 433 mg/dL·min, AL: 3,712 ± 590 mg/dL·min,
and AH: 3,014 ± 454 mg/dL·min (Fig. 2-b). The iAUC tended
to lower the model food AH by 35.7 % compared to thestandard food (p < 0.1).

Olive oil intake and PPHG suppression
The subjects were the same as participants in the salad
chicken test. The test food was olive oil (B). The change in
ΔBG after starting the test is shown in Fig. 1-b. The averagevalues of ΔBG from 45 to 120 min were lower in the model
foods BL and BH than in the standard food, but it was not
significant.
The ΔCmax was 62.7 ± 4.3 mg/dL for the standard
food, 62.8 ± 5.0 mg/dL for BL, and 56.0 ± 7.7 mg/dL for
BH, and no differences were observed (Fig. 2-a). The iAUC
was standard food: 4,690 ± 433 mg/dL · min, BL: 4,085 ±400 mg/dL · min, BH: 3,811.5 ± 549 mg/dL · min, and nodifference was observed (Fig. 2-b).

Grain vinegar intake and PPHG suppression
The subjects were the same as the two study participants
described above. The test food was grain vinegar (C). Thechange in ΔBG after starting the test is shown in Fig. 1-c.
The average values of ΔBG from 30 to 120 min were lower
in the model foods CL and CH than in the standard food.
Particularly, the ΔBG at 30 min in CH was 29.0 ± 3.2 mg/dL,
which was 20.1 mg/dL lower (p < 0.05) compared to that of
the standard food (49.1 ± 5.4 mg/dL), also the ΔBG at 45 mintended to be lower ( p < 0.01).
ΔCmax was 62.7 ± 4.3 mg/dL for the standard food,54.8 ± 3.9 mg/dL for CL, and 41.2 ± 3.9 mg/dL for CH (Fig.
2-a). The iAUC was standard food: 4,690 ± 433 mg/dL · min,

CL: 3,780 ± 371 mg/dL · min, CH: 3,280 ± 358 mg/dL · min(Fig. 2-b). The iAUC of CH was lower by 30.1% than that of
the standard food (p < 0.05).

Indigestible dextrin intake and PPHG suppression
The subjects were the same as the three study
participants described above. The test food was indigestible
dextrin (D). The change in ΔBG after starting the test is
shown in Fig. 1-d. The average values of ΔBG at each time
were almost the same as that of the standard food when themodel food DL was ingested. The average values of ΔBG
from 30 to 120 min were lower in the model food DH than in
the standard food, but it was not significant.
ΔCmax was 62.7 ± 4.3 mg/dL for the standard food,53.0 ± 5.6 mg/dL for DL, and 64.0 ± 4.2 mg/dL for DH, andno difference was observed ( Fig. 2-a). The iAUC wasstandard food: 4,690 ± 433 mg/dL · min, DL: 3,848 ± 503
mg/dL · min, and DH: 4,694 ± 407 mg/dL · min (Fig. 2-b).

Cabbage intake and PPHG suppression
The subjects were the same as the four study participants
described above. The model food was cabbage (E). The change
in ΔBG after starting test is shown in Fig. 1-e. There was no
significant difference in ΔBG from 0 to 120 min between
groups.
ΔCmax was 62.7 ± 4.3 mg/dL for the standard food,
DL: 63.6 ± 5.3 mg/dL for DL, and 61.3 ± 4.0 mg/dL for DH(Fig. 2-a). The iAUC was standard food: 4,690 ± 433 mg/
dL·min, DL: 4,755 ± 499 mg/dL·min, and DH: 4,478 ± 353
mg/dL·min (Fig. 2-b).

Vinegared rice intake and PPHG suppression
Out of 20 total participants, 11 subjects (2 males,
9 females, 23.1 ± 1.3 years, 159.7 ± 8.9 cm, 52.3 ± 7.0 kg,

Fig. 2. The amount of ΔCmax (a) and iAUC (b) after intaking test food.

Results are expressed as mean ± standard error, n = 10, † p < 0.1, * p < 0.05, ** p < 0.01 vs standard food, Bonferroni test. ΔCmax,
maximum blood glucose level change; iAUC, incremental area under the curve of blood glucose level change. See Figure 1 for group names.

_ 225 _

Food Materials and Postprandial Hyperglycemia

BMI 20.5 ± 1.6 kg/m 2 ) participated in the study. The test
food was vinegared rice (F). The change in ΔBG after thestarting test is shown in Fig. 3-a. The values of ΔBG in F
were significantly lower by 27% at 45 min and by 28% at 60
min (p < 0.05) compared to the standard food. ΔCmax was
significantly lower by 19.3% (p < 0.01) and iAUC tended to
be lower by 19.7 % (p < 0.1) in F.

The ΔCmax in G was significantly lower by 36.7 % (p< 0.01), and the iAUC was significantly lower by 32.0 % (p< 0.05) than that of the standard food (Fig. 4-b). The ΔCmax
in H was significantly lower by 34.9 % ( p < 0.01), and theiAUC was significantly lower by 21.8 % (p < 0.05) than thatof the standard food.

Gyoza + Ponzu soy sauce intake and PPHG
suppression

Fried chicken intake with or without lemon juice
and PPHG suppression

The subjects were the same as the study participants inthe complex foods G and H described above. The complex
food was gyoza + ponzu soy sauce (I). The change in ΔBG
after starting test is shown in Fig. 3-c. The values of ΔBG
in complex food I were significantly lower by 52.0 % at 15
min (p < 0.05), by 55.6% at 30 min (p < 0.01), by 50.4% at
45 min (p < 0.01), and by 41.3% at 60 min (p < 0.01). The
ΔCmax was significantly lower by 44.4%, and the iAUC wassignificantly lower by 39.7 % than that of the standard food( p < 0.01, Fig. 4-c).

Out of 20 total participants, 14 subjects (5 men, 9 women,
23.0 ± 1.3 years, 162.5 ± 9.9 cm, 56.3 ± 10.7 kg, BMI 21.2
± 2.1 kg/m2 ) participated in the study. The test foods werefried chicken (G) and fried chicken + lemon juice (H).
The change in ΔBG after starting test is shown in Fig. 3-b.
The average values of ΔBG from 30 to 90 min were lower
in the complex foods G and H than in the standard food.
Specifically, the values of ΔBG in G and H at 30, 45, 60 min
were significantly lower than that in the standard food.

(a)ΔBlood glucose（mg/dL）

70

80

Standard food

60

F

50
40
30
20
10

Standard food
G

60
50

H

40
30
20
10

0

0

0

80

30

(c)

70
ΔBlood glucose（mg/dL）(b)70
ΔBlood glucose（mg/dL）

80

60
Time（min）

90

0

120

30

60

90

120

Time（min）

Figure 3(b)Figure 3(a)Standard food

60
I

50
40
30
20
10
0
0

30

60
Time（min）

90

120

Figure 3(c)Fig. 3. Fluctuation of the blood glucose level at the time of intaking test food ahead of rice.
a) F. b) G and H. c) I. Results are expressed as mean ± standard error, a) n = 11, paired t-test, b) n = 14, Bonferroni test, c) n =14, paired t-test, * p < 0.05, ** p < 0.01 vs standard food. Standard food, cooked rice 200 g; F, vinegarded rice; G, fried chicken 135 g
before cooked rice 149 g; H, fried chicken 135 g + lemon juice 15 g before cooked rice 145 g; I, Japanese dumplings (gyoza) 138 g +ponzu soy sauce 15 g before cooked rice 129 g.

_ 22 6 _Glycative Stress Research

Fig. 4. The amount of ΔCmax after intake of test food.
a) F. b) G and H. c) I. Results are expressed as mean ± standard error, a) n = 11, paired t-test, b) n = 14,
Bonferroni test, c) n = 14, paired t-test, * p < 0.05, ** p < 0.01 vs standard food. ΔCmax, maximum blood
glucose level change. See Figure 3 for group names.

Discussion

Lipid intake and PPHG

Protein intake and PPHG

Olive oil (model food B) was used to examine theeffect of lipid intake on PPHG. PPHG was not significantly
inhibited by intake of the model food B as compared withthe standard food (Fig. 1-b, Fig. 2).
Similar to protein and lipids, the main components ofmodel food B promote GLP-1 secretion, thus suppressing
gastric motility and PPHG 17). However, another report 18)
showed that lipids do not promote insulin secretion despite
the increase in GLP-1 concentration and they speculated thatthe suppressing effect on gastric motility may be too strong
to elevate blood glucose and stimulate insulin secretion. In
addition, it has been reported that protein intake suppresses
PPHG by 2 to 3 times stronger compared to lipids, and there
is no synergistic effect between the two 19). In this study, we
conducted a test by ingesting lipids alone, but it is possiblethat the effect of lipids on PPHG was small.

Salad chicken (model food A) was used to examine thesuppressive effect of protein intake on PPHG. A decreasein ΔBG, Cmax, and iAUC was observed depending on theintake of model food A ( Fig. 1-a, Fig. 2). The intake of model
food AH before the rice significantly suppressed PPHG,
which was considered to be an effect of the components
contained in model food A. The amount of protein in thetest food calculated from model food A intake was 11.5 g inmodel food AL and 23 g in model food AH (Table 3).
The protein, rich in model food A, are reported topromote secretion of gastrointestinal hormones including
GIP (glucose-dependent insulinotropic polypeptide) andGLP-1 (glucagon-like peptide-1) 16). GLP-1 promotes insulin
secretion from pancreatic β-cells as an incretin, cooperated
with GIP, in a blood glucose-dependent manner, and GIP
influences gastric peristalsis, reduces gastric emptying
and delays glucose elevation. This study also indicated that
protein intake significantly suppressed PPHG, and that its
action became stronger as intake increased.

Acetic acid and PPHG
Grain vinegar (model food C) was used to verify theeffect of acetic acid on PPHG. A decrease in ΔBG, Cmax,_ 227 _

Food Materials and Postprandial Hyperglycemia

and iAUC was observed depending on the intake amount ofmodel food C (Fig. 1-c, Fig. 2). Therefore, it was consideredthat this suppressive action was the effect of the components
contained in the model food C.
The amount of acetic acid in the test food calculated
from the model food C was 0.63 g in model food CL and 1.26
g for the model food CH (Table 3). The amount of acetic
acid useful for suppressing PPHG when ingesting 200 g ofrice was estimated to be at least 0.63 g.
Acetic acid contained in vinegar has been confirmed inexperiments in a rat model to prolong the gastric detention
time and delay digestion and absorption 20). In addition, a newphysiological action is indicated that acetic acid activates
AMP kinase and it leads to a reduction in blood glucose
due to inhibition of gluconeogenesis 21). From the results ofthe model food C study, acetic acid significantly suppressed
PPHG and its action became stronger according to the intake
amount.

Soluble dietary fiber and PPHG
Indigestible dextrin (model food D) was used to examine
the effect of water-soluble dietary fiber on PPHG.
Even when the model food D was ingested prior the riceintake, no significant suppressing effect on PPHG was observed
as compared with the standard food (Fig. 1-d, Fig. 2).
Regarding the inhibitory effect on PPHG of watersoluble dietary fiber, which is the main component ofmodel food D, there are detailed studies by Jenkins DJA
et al. 22), Doi K et al. 23) and Ebihara K et al. 24), in which it isconsidered that water is absorbed in the digestive tract andthe gastric contents become viscous, resulting in a longer
gastric detention time, thus suppressing PPHG. Despite thelow viscosity of indigestible dextrin, it is suggested that it
improves glucose tolerance in rats and healthy individuals,
and that repeated intake can be expected to correct disordersof glucose metabolism seen in patients with obesity 25-31).
Since the glucose tolerance improving effect of indigestible
dextrin appears selectively in disaccharides, i.e., sucrose,
maltose, it is considered that these actions do not depend
only on viscosity 25, 26, 29).
Disaccharides are decomposed into monosaccharidesby α-glucosidase, a digestive enzyme, and absorbed by bloodvessels in the small intestine. When indigestible dextrin
binds to disaccharide-linked α-glucosidase as an inhibitor,
the inversion of α-glucosidase, containing two hydrolyzed
monosaccharides, to the bloodstream side is blocked; later,
the bound monosaccharides are released from the intestinal
wall to the digestive tract with a delayed decrease in affinity.
This reaction is presumed to be a mechanism of PPHG
suppression by indigestible dextrin 5).
Another report showed that, in tests loaded with a starchdiet, there was a significant difference in blood glucose level
between the control and the test food in the high glucose
group with Cmax in control above the mean value, while
there was no significant difference in the low glucose groupwith Cmax below the average. In contrast in the sucrose
tolerance test, a significant difference was found not only inthe high glucose group but also in the low glucose group 5).
These findings indicate that the affinity of indigestible
dextrin is stronger for the sucrose-bound intermediate, as
an inhibitor, than for the maltose-bound intermediate. Since

starch (maltose hydrolyzate) is the main component ofcooked rice used in this study, the sugar absorption inhibitory
effect of indigestible dextrin was perhaps unremarkable,compared with the effect of protein or acetic acid.

Dietary fiber and PPHG
Cabbage (model food E) was used to examine the effectof ingestion of both insoluble dietary fiber and water-soluble
dietary fiber on PPHG. When the model food E was ingested
before the rice intake, no significant suppressing effect on
PPHG was observed as compared with the standard food (Fig.
1-e, Fig. 2).
According to the Food Composition Table 32), cabbage
contains 0.4 g of water-soluble dietary fiber and 1.4 g ofinsoluble dietary fiber per 100 g of edible portion. Generally,
it is the water-soluble dietary fiber that has the suppressing
effect on PPHG, while the insoluble dietary fiber is not
involved. It is considered that the water-soluble dietary fiber
absorbs water in the digestive tract, thus the gastric contents
have viscosity and pass slower through the digestive tract,resulting in suppression of PPHG. There is a similar study
that verified the suppressing effect on PPHG by the intake
sequence of vegetable salad in diabetic patients 9). In thisstudy, however, the subjects ate rice 10 min after vegetablesalad intake. In this experiment, there is a difference inconditions because no time was left between the shredded
cabbage and rice.
Furthermore, in the above research, a vegetable salad
was ingested with a dressing containing seasonings such as
rice vinegar and olive oil. Therefore, it is considered that not
the dietary fiber contained in the vegetable salad but the acetic
acid and the lipids contained in the dressing were involved in
the PPHG suppression. Also, it has been reported that healthy
young subjects who ate 50 g of vegetable salad before rice
had similar blood glucose levels to those without vegetablesalad, and did not suppress PPHG 33). From these results, it wasinferred that the PPHG inhibition by dietary fiber was dosedependent, and it was necessary to ingest a larger amount of
dietary fiber in order to obtain moderating effect on PPHG.
It is considered that the intake timing and intake amountof dietary fiber are important in order to exert the action ofdelaying the decomposition and absorption of carbohydrates.

Effect of complex foods on PPHG
In this study, we examined the PPHG suppressing effectof complex foods containing various nutritional components
which include vinegared rice (complex food F ), fried chicken(complex food G), fried chicken + lemon juice (complex
food G), and gyoza + ponzu soy sauce (complex food I).
The results showed that all the complex foods significantly
suppressed PPHG (Fig. 3-5).
Focusing on iAUC, the complex food F decreased by
19.7 % compared to intake of the standard food. Complex
food G decreased by 32.0 % and complex food H by 21.8%.
In addition, complex food I decreased by 39.7%.
The sushi vinegar used to cook Complex food F
contained 0.6 g of acetic acid (Table 4 ). This acetic acidcontent is compatible with the dose (0.63 g) useful forsuppressing PPHG when ingesting 200 g of rice in the model
food CL. The concurrent intake of rice and acetic acid as_ 22 8 _Glycative Stress Research

Fig. 5. iAUC after intake of test food.
a) F. b) G and H. c) I. Results are expressed as mean ± standard error, a) n = 11, paired t-test, b) n = 14,
Bonferroni test, c) n = 14, paired t-test, † p < 0.1, * p < 0.05, ** p < 0.01 vs standard food. iAUC, incremental
area under the curve of blood glucose level change. See Figure 3 for group names.

vinegared rice significantly suppressed PPHG in this study
as well as in the study of the concurrent intake of rice andbeef bowl ingredients, rich in protein and lipids, which also
showed PPHG suppression 10, 11). This indicates that even if
carbohydrates and acetic acid are concurrently ingested as acomplex food, the actions of delaying digestion/absorption
and suppressing gluconeogenesis due to acetic acid exhibit
similar effects as those of prior ingestion.
The complex food G contains 16.6 g more protein and13.4 g more lipids than in standard food ( Table 5 ). Even
if the model food AL (protein: 11.5 g) and the model food
BL (lipid: 14 g) were individually taken before rice, there
was no significant difference in blood glucose comparedto the standard food. By ingesting protein and lipids as acomplex food such as fried chicken, it may be possible thatthe nutritional content of each synergistically contributed
to PPHG suppression. On the other hand, no difference wasobserved in the effect between the complex foods G and H.
Regarding the lemon juice, 30 g was effective, but not 15 g 12).
Lemon is rich in organic acid, mainly citric acid, andpolyphenols, which may play a role in PPHG suppression. In
this study, however, the effect of lemon juice seemed unclear
possibly due to the effect of fried chicken alone being strong
enough to mask the synergistic action, if any was induced by
15 g lemon juice.
The complex food I contains 8.1 g of protein, 16.2 gof lipids, 0.3 g of acetic acid, and 2 g of dietary fiber morethan in the standard food (Table 4 ). It is possible that eachnutrition component synergistically contributed to PPHG
suppression by ingesting a complex food with well-balanced
nutrition in a similar manner as prior intake of fried chicken.
In order to control blood sugar levels, it is necessary
to combine diet therapy, exercise therapy, and drug therapy
among which a diet therapy is the most basic for type 2
diabetes. It is necessary to respond flexibly while respecting
individual eating habits and preferences for the purposeof a successful long-term diet. In the “Diabetes Practice
Guideline 2019”, a guideline for diabetes treatment issued
by the Japan Diabetes Society 3), there are descriptions about
energy intake, distribution of three major nutrients, salt
intake, and dietary fiber intake. However, almost no mention
is made of the specific dietary content or the nutritional
interaction. The purpose of the diabetic diet is to reduce
blood glucose to a target level and its daily fluctuation, i.e.,
glucose spike, to prevent complications, therefore, a dietthat is balanced in desirable energy intake and nutrition isimportant. Complex foods such as fried chicken and gyoza
have strong control actions on PPHG, as shown in this study.
Additionally, they contain a variety of nutrition, and are easy
to incorporate even when eating out. Therefore, we consider
that these are side dishes that can be expected to suppress
PPHG easily in the daily diet.

_ 22 9 _Food Materials and Postprandial Hyperglycemia

Research limitation
The subjects of this study were aged 23.3 ± 1.8 years
and whose glucose tolerance was within the standard range.
It has been reported that young people do not have large
PPHG and are less likely to exhibit the suppressive effect offunctional foods than middle-aged people 34). Therefore, thestrength of food actions evaluated may change dependingon the age of the subject. Also, since only the fasting insulin
was measured before the test, it was not possible to verify
the changes in the hormone secretion induced by intake ofthe test food. In the future, it is necessary to evaluate thechronological changes of hormone secretion concurrently
with blood glucose.

rice (standard food), which had a more pronounced effectas the intake amounts of the test foods were increased. It
was suggested that these phenomena involved the actionof protein to promote incretin secretion and the action ofacetic acid to delay digestion and absorption, and to suppress
gluconeogenesis, and that the effect depends on the intake
amount. On the other hands, if olive oil, indigestible dextrin,and cabbage were ingested prior to rice, no significant
difference was observed in PPHG in the young subjects.

Conflict of Interest Statement
The authors claim no conflict of interest in this study.

Conclusion
The present study showed that healthy young men andwomen had significantly suppressed PPHG by consuming
salad chicken and cereal vinegar as test foods before eating

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