Table 2 Characteristics of RCTs included in the meta-analysis of whole grain intake and glycemic control in adults

Ding et al. 2022 [68]

parallel

I: 45;

C: 54

F:40;

M:55

China

I: 64.9 ± 4.09;

C: 64.8 ± 6.47

I: 25.7 ± 2.9;

C: 25.6 ± 3.5

T2DM

12

100 g/day germinated brown rice

100 g/day refined white rice

1–2

FBG, HbA_1C

Xue et al., 2021 [67]

parallel

I: 80;

C: 78

F: 126;

M: 32

China

I: 44.5 ± 12.5;

C: 45.4 ± 14.0

I: 24.3 ± 3.9;

C: 24.1 ± 4.2

healthy/overweight

12

154 g/d whole grain rye crisp bread + whole grain rye puffs

142.8 g refined wheat crisp + refined wheat puffs

1–2

FBG, FBI, HOMA-IR, HbA_1C

Ren et al., 2020 [66]

parallel

I1: 28; I2: 28; I3: 28; C: 28

NA

China

18–70

NA

MetS

4

I1: 50 g Paddy rice with the husk removed + 50 g polished rice

I2: 50 g Hot-air drying germinated brown rice + 50 g polished rice

I3: 50 g autoclaving germinated brown rice + 50 g polished rice

100 g polished rice

1–2

FBG

Mai et al., 2020

[65]

parallel

I: 40; C: 40

F: 64; M: 16

Vietnam

I: 65.2 ± 3.78;

C: 65.0 ± 3.85

I: 25.9 ± 2.4;

C: 25.5 ± 2.3

MetS

12

200 g cooked pregerminated brown rice

200 g white rice

1–2

FBG, FBI, HOMA-IR

Roager et al., 2019

[64]

crossover

50

F: 32; M: 18

Danish

48.6 ± 11.1

28.9 ± 3.6

at risk of MetS

8

whole grain mix (ingredient: 179 g/day)

refined grain diet

≥ 5

FBG, FBI, HOMA-IR, HbA_1C

Malik et al., 2019

[22]

crossover

112

NA

India

37.1 ± 9.4

28.1 ± 3.4

overweight

12

parboiled brown rice; total whole grain: 31.1 g/day

white rice; total whole grain: 15.7 g/day

1–2

FBG, FBI, HOMA-IR, HbA_1C

Kuroda et al., 2019

[63]

parallel

I: 17; C: 17

F: 15; M: 19

Japan

I: 70.5 ± 0.9;

C: 75.4 ± 1.1

I: 24.8 ± 0.6;

C: 22.5 ± 0.5

healthy

104

100 g/d ultra-high hydrostatic pressurizing brown rice

100 g/d polished white rice

1–2

FBG, HbA_1C

Hoevenaars et al., 2019

[62]

parallel

I: 25; C: 25

F: 31; M: 19

Netherlands

I: 28.0 ± 2.1;

C: 27.6 ± 2.6

I: 47–69; C: 51–70

overweight and obese men and postmenopausal women

12

whole grain wheat cereals and ready-to-eat-cereals (ingredient: 98 g/day)

refined wheat

1–2

FBG, FBI, HOMA-IR

Kikuchi et al., 2018

[61]

parallel

I: 24; C: 25

F: 17; M: 32

Japan

I: 48.1 ± 1.6; C: 47.0 ± 1.7

I: 27.1 ± 0.7; C: 27.7 ± 0.48

healthy

12

whole grain wheat bread

(ingredient: 100 g/day)

100 g/day refined wheat bread

1–2

FBG, FBI

Karl et al., 2017

[60]

parallel

I: 41; C: 40

F: 32; M: 49

USA

I: 55 ± 6; C: 54 ± 5

I: 25.7 ± 3.9; C: 25.7 ± 3.2

healthy

6

whole grain mix: (ingredient: 207 g/day)

refined grain-based diet; (ingredient: 0 g/day)

≥ 5

FBG, FBI, HOMA-IR

Nakayama et al., 2017

[23]

crossover

8

F: 4; M: 12

Japan

64.0 ± 8.8

25.7 ± 5.6

type 2 diabetes

8

277 g/day cooked glutinous brown rice

277 g/day cooked white rice

1–2

HbA_1C

Kristensen et al., 2017

[59]

parallel

I: 81; C: 88

F: 169

France

I: 36.2 ± 10.1; C: 35.3 ± 8.7

I: 30.2 ± 1.9; C: 30.1 ± 2.0

overweight/obese

12

whole grain mix: 80 g/day

Refined grain

≥ 5

FBG, FBI, HbA_1C

Kondo et al., 2017

[58]

parallel

I: 14; C: 14

F: 18; M: 10

Japan

I: 65.2 ± 8.7; C: 68.1 ± 6.8

I: 24.2 ± 3.5; C: 25.0 ± 3.7

type 2 diabetes

8

brown rice: for 10 out of 21 meals per week

white rice

1–2

FBG, FBI, HOMA-IR, HbA_1C

Cooper et al., 2017

[24]

parallel

I: 35; C: 10

F: 25; M: 21

USA

I: 26.2 ± 1.0; C: 24.6 ± 1.6

I: 22.8 ± 0.5; C: 25.5 ± 2.1

healthy

6

6 servings/day whole grain products

refined grain

≥ 5

FBG

Vetrani et al., 2016

[57]

parallel

I: 26; C: 28

F: 24; M: 16

Italy

I: 57.2 ± 1.9; C: 58.4 ± 1.6

I: 32.1 ± 1.4; C: 31.5 ± 1.3

overweight/obese, MetS

12

whole grain mix (ingredient: 136 g/day)

refined grain

≥ 5

FBG, FBI, HOMA-IR

Kirwan et al., 2016

[56]

crossover

33

F: 27; M: 6

USA

39 ± 7

33.1 ± 4.3

overweight/obese

8

complete whole grain mix (ingredient : 93 g/day)

refined grain mix

≥ 5

FBG, FBI, HOMA-IR, HbA_1C

Geng et al., 2016

[55]

parallel

I: 94; C: 97

F: 96; M: 95

China

I: 56.7 ± 6.8; C: 56.7 ± 6.7

I: 25.6 ± 3.0; C: 25.9 ± 2.8

hyperlipidemia

12

150 g/day pre-germinated brown rice

equivalent staple food products

1–2

FBG

Connolly et al., 2016

[54]

crossover

30

F: 19; M: 11

England

42

26.4 ± 5.7

at risk of cardio-metabolic disease

6

45 g/day of whole grain oat Granola

non-whole grain

1–2

FBG, FBI, HOMA-IR

Ampatzoglou et al., 2016

[53]

crossover

33

F: 21; M: 12

England

48.8 ± 1.1

27.9 ± 0.7

healthy

6

whole grain mix

(ingredient: 168.4 g/day)

diet low in whole grain

≥ 5

FBG, FBI

Vitaglione et al., 2015

[52]

parallel

I: 36; C: 32

F: 45; M: 23

Italy

I: 40 ± 2; C: 37 ± 2

I: 30.0 ± 0.5; C: 29.5 ± 0.4

overweight/obese

8

62 g/day whole grain wheat biscuit

refined wheat products

1–2

FBG

Jackson et al., 2014

[51]

parallel

I: 25; C: 25

F: 25; M: 25

USA

I: 46.4 ± 5.9; C: 45.8 ± 6.0

I: 32.9 ± 3.5; C: 33.5 ± 4.0

Overweight/obese, at risk of metS

12

232 g/day whole grain products

refined grain

≥ 5

FBG, FBI, HOMA-IR

Bui et al., 2014

[50]

parallel

I: 30; C: 30

F: 60

Vietnam

I: 56.9 ± 5.8; C: 56.6 ± 5.0

I: 23.9 ± 3.0; C: 23.5 ± 3.2

pre-diabetes

16

pre-germinated brown rice (PGBR)

white rice

1–2

FBG

Wang et al., 2012

[49]

parallel

I: 29; C: 28

F:38; M:19

USA

I: 55 ± 9; C: 50 ± 9

I: 26.5 ± 3.0; C: 25.0 ± 2.2

pre-diabetes

12

brown rice as staple food

white rice

1–2

FBG, FBI, HbA_1C, HOMA-IR

Mackay et al. a, 2012

[48]

crossover

14

F:4; M: 10

Canada

53 ± 6

26.5 ± 2.9

Normoglycemic/ normoinsulinemic

6

162.5 g/day whole grain wheat sourdough

168.8 g/day white bread

1–2

FBG

Mackay et al. b, 2012

[48]

crossover

13/14

F:4; M: 10

Canada

57 ± 7.4

35.7 ± 5.65

pre-diabetes

6

162.5 g/day whole grain wheat sourdough

168.8 g/day white bread

1–2

FBG

Kristensen et al., 2012

[47]

parallel

I: 38; C: 34

F: 72

Denmark

I: 59.1 ± 5.6; C: 60.3 ± 5.3

I: 30.0 ± 0.4; C: 30.4 ± 0.6

overweight/obese

12

150 g/day whole grain wheat bread/pasta/biscuits (ingredient: 105 g/day)

refined wheat

1–2

FBG, FBI, HOMA-IR, HbA_1C

Zhang et al., 2011

[46]

parallel

I: 101; C: 101

F: 94; M: 108

China

I: 49.6 ± 6.7; C: 49.8 ± 7.1

I: 25.9 ± 3.4; C: 25.4 ± 2.5

diabete/at risk of diabetes

16

100 g/day brown rice

white rice

1–2

FBG, FBI, HOMA-IR, HbA_1C

Tighe et al., 2010

[45]

parallel

I1: 73; I2:70; C: 63

F: 102; M: 104

England

I1: 51.6 ± 0.8; I2: 52.1 ± 0.9; C: 51.8 ± 0.8

I1: 28.0 ± 0.5; I2: 27.0 ± 0.4; C: 28.0 ± 0.5

healthy adults

12

I1: 3 servings of whole wheat products: 70–80 g whole grain bread + 30–40 g whole grain cereals; I2: 1 serving of whole wheat products and 2 servings of oats products

refined grain mix

≥ 5

FBG, HOMA-IR

Giacco et al., 2010

[44]

crossover

15

F:3 M: 12

Italy

54.5 ± 7.6

27.4 ± 3.0

healthy

3

whole grain wheat products

refined wheat products

≥ 5

FBG, FBI, HOMA-IR

Brownlee et al., 2010

[43]

parallel

I1: 85; I2: 81; C: 100

F: 133; M: 133

England

I1: 45.9 ± 10.1; I2: 45.7 ± 9.9; C: 45.6 ± 10

I1: 30.0 ± 3.7; I2: 30.3 ± 4.5; C: 30.0 ± 4.0

adults with BMI > 25

16

I1: 60 g/day whole grain products for 16 weeks; I2: 60 g/day whole grain products for 8 weeks followed by 120 g/day whole grain products for 8 weeks

consuming < 30 g/day whole grain products

≥ 5

FBG, FBI

Kim et al., 2008

[42]

parallel

I: 23; C: 24

F: 47

Korea

20–35

I: 27.57 ± 0.43; C: 27.27 ± 0.59

overweight women

6

mixture of brown rice and black rice 3 meals per day

white rice

1–2

FBG, FBI

Katcher et al., 2008

[41]

parallel

I: 24; C: 23

F: 23; M: 24

USA

I: 45.4 ± 8; C: 46.6 ± 9.7

I: 35.5 ± 4.1; C: 36.1 ± 4.9

obese adults with MetS

12

5 servings/day; obtain all of their grain servings from whole grains

<0.2 servings/day; avoid whole grain products

≥ 5

FBG, FBI

Andersson et al., 2007

[40]

crossover

30

F: 22; M: 8

Sweden

59 ± 5

28.3 ± 2.0

moderately overweight adults and/or with abdominal obesity

6

whole grain products (ingredient: 112 g/day)

refined grain

≥ 5

FBG, FBI

McIntosh et al., 2003

[39]

crossover

28

M: 28

Australia

40–65

30 ± 0.9

overweight men

4

products containing whole grain rye flour and wheat flour (ingredient: 88 g)

low-fiber refined cereal products

≥ 5

FBG, FBI

Li et al., 2003

[38]

crossover

10

F: 10

Japan

20.4 ± 1.3

19.2 ± 2.0

healthy

4

70% rice and 30% barley mixture

100% rice

1–2

FBG, HbA_1C

Pins et al., 2002

[37]

parallel

I: 45; C: 43

F: 43; M: 45

USA

I: 48.7 ± 16.9; C: 46.4 ± 15.3

I: 31.2 ± 5.1; C: 30.6 ± 4.7

Men and women being treated for hypertension

12

60 g Quaker oatmeal + 77 g Quaker oat squares

65 g Malt-O-Meal hot wheat cereal + 81 g Kellogg’s crispix

1–2

FBG

Pereira et al., 2002

[36]

crossover

11

F:6; M:5

USA

41.6 ± 2.67

30.2 ± 1.01

overweight and obese hyperinsulinemic adults.

6

whole grain mix (ingredient: 356 g/day)

refined grain mix

≥ 5

FBG, FBI, HOMA-IR

Hawrysh et al., 1998

[35]

crossover

11

M: 11

Canada

51 ± 6.5

27.4 ± 0.1

type 2 diabetes patients

12

83 g/day waxy hulless barley bread

white bread

1–2

FBG, FBI, HbA_1C