Table 2.
Summary findings from randomized control trials based on the impact of soy on hyperglycemia.
| Study | Sample Size & Population | Duration | Treatment | Dose; Format | Results | Conclusions |
|---|---|---|---|---|---|---|
| [89] | 389 osteopenic postmenopausal women | 2 years, parallel RCT | Genistein extract with calcium and Vitamin D3 supplement compared to placebo | Purified supplement (54 mg/day) | Significant reductions in FBG, insulin, HOMA-IR, fibrinogen, F2-isoprostanes, soluble intercellular adhesion molecule-1, and soluble vascular cellular adhesion molecule-1 | Genistein supplements improve markers of glycemic control and other markers of CVD risk |
| [97] | 42 postmenopausal women with MetS | 8 weeks, randomized crossover trial | Control diet (Dietary Approaches to Stop Hypertension, DASH); DASH diet with red meat replaced with soy nuts; DASH diet with red meat replaced with soy protein | 30 g soy nut = 1 serving read meat; 30 g soy protein = 1 serving red meat. Normal diet for 3 weeks followed by all 3 diets for 8 weeks each, with 4-week washout period in between each diet | Soy nuts reduced HOMA-IR and fasting plasma glucose more than soy protein (p < 0.01 for both factors) and control (p < 0.01 for both factors) | Soy nuts have greater role in attenuating blood glucose response markers compared to soy protein in postmenopausal women with MetS |
| [96] | 75 women with MetS, age 60–70 | 12 weeks, parallel RCT | Soy nuts; textured soy protein (TSP) | 35 g/day soy nut; 35 g/day textured soy protein | Compared to control, serum FBG, HOMA-IR and insulin were lower in soy-nut group (p < 0.05, p < 0.1, p < 0.05) and the mean changes were higher in soy nut group vs. TSP (p < 0.001) | Soy nut leads to greater reductions in markers of glycemic control than soy protein |
| [88] | 203 postmenopausal women, age 48–62. | 1 year parallel RCT | Calcium tablet with isoflavones | 40 or 80 mg isoflavones/day compared to calcium with 0 mg isoflavones | Both treatment groups significantly lowered FBG. No dose-response effect. No effect on lipids | Isoflavone supplementation favourably influences FBG in postmenopausal women |
| [90] | 180 postmenopausal women with hyperglycemia | 6 months parallel RCT | Soy protein isolate with or without isoflavone conjugates | 15 g soy protein and 100 mg isoflavones, 15 g milk protein and 100 mg isoflavones, or 15 g milk protein | No significant improvements in fasting and 2-h postload glucose, fasting and postload insulin, glycated serum protein, HOMA-IR. and beta-cell function | Soy protein isolate with or without isoflavones does not improve glycemic control and insulin sensitivity |
| [99] | 20 healthy males and females | 1 day; within-subject design with 1 week intervals in between interventions | Intervention (1) Bar-type cake made of whole soy powder; (2) cooked paddy-rice; (3) cooked paddy rice with whole soy powder cake | 114 g whole soy powder cake containing 50 g carbohydrates, 144 g cooked paddy-rice containing 50 g carbohydrates; 144 g cooked paddy-rice with 60 g whole soy powder sake | (1) Blood glucose and insulin levels were lower than control (2) Blood was lower, while insulin levels were increased slightly | Postprandial blood glucose and insulin response may be improved with whole soy powder food; beneficial effects of combining soy products with carbohydrate-rich foods are less clear |
| [87] | 120 postmenopausal women with Metabolic Syndrome (60 received treatment; 60 received placebo) | 1 year, randomized, double-blind, placebo-controlled trial | Genistein | 54 mg/day in 2 tablets | Fasting blood glucose, fasting insulin and HOMA-IR were significantly decreased in the treatment group (p < 0.001) | Soy isoflavone, genistein, significantly lowers hyperglycemia and reduces insulin resistance |
| [98] | 10 type 2 diabetes patients in the 80 kcal meal tolerance test (Study 1); 11 diabetic patients in the 592 kcal meal tolerance test (Study 2) | 1 day, crossover study | Soybean nutrition bar | Study 1: 1 soybean nutrition bar containing 7.0 g carbohydrates, 4.3 g fat, 1.9 g fiber, 2.7 g protein, 8.2 mg isoflavones Study 2: 4.3 soybean nutrition bars, each containing 50.9 g carbohydrates, 31.3 g fat, 14.4 g fiber, 19.6 g protein, 14 mg isoflavones | Blood glucose was lower in both studies with the soybean nutrition bar intervention (p < 0.001); Insulin AUC was lower than the control in study 2 only; no significant changes in blood TGs and non-esterified fatty acids between treatment and control groups in either study | Soybean nutrition bars may have a role in preventing postprandial hyperglycemia in patients with type 2 diabetes compared to isocaloric cookies |
| [91] | 165 women with impaired glucose regulation, aged 30–70 | 24 week parallel RCT | Soy protein with or without daidzein or genistein extract | 10 g soy protein without isoflavones, or with 50 mg daidzein, or 50 mg genistein | No significant changes in FBG, 2-h glucose, HbA1c, fasting, and 2-h insulin, AUC of glucose and insulin. | Purified extracts of daidzein and genistein do not improve glycemic control and insulin sensitivity |
AUC = area under blood glucose response curve; CVD = cardiovascular disease; FBG = fasting blood glucose; HBA1c = glycated hemoglobin; HOMA-IR = homeostatic model assessment of insulin resistance; RCT = randomized controlled trial; MetS = metabolic syndrome.