Soy Protein and Diabetes Health

Doctor’s Advice
Ask the Expert…
Bob Blair, Ph.D. & Aaron Tabor, M.D.

Evidence is emerging that dietary isoflavones play a beneficial role in the management of diabetes. Adding soy to the diet provides a wide range of health benefits, many of which are applicable to a person with diabetes. Benefits include favorably altering insulin resistance, glycemic control, and serum lipid control, which can improve the cardiovascular risk profile.

In a randomized, double blind, cross-over trial of dietary soy supplementation (Jayagopal et al., 2002) 32 women with diet controlled type 2 diabetes received 30 grams of soy protein per day (containing 132 mg isoflavones) or placebo for 12 weeks. When compared with the mean percentage change from baseline seen after 12 weeks of placebo, isoflavone supplementation resulted in significantly lower mean values for fasting insulin (P = 0.006), insulin resistance (P = 0.003), HbA1C (P = 0.048), total cholesterol (P = 0.004), LDL cholesterol (P = 0.001), HDL/LDL ratio (P = 0.015) and free thyroxine (P = 0.004).

In a recent cross-sectional study of Chinese women in Shanghai, the relationship between dietary soy intake and the risk of developing glycosuria, a risk factor for diabetes, was examined. In this study, it was reported that higher levels of soy intake were associated (P for trend = 0.05) with a decreased risk of glycosuria in postmenopausal women with a low BMI (Yang et al., 2004).

One potential reason for soy’s apparent beneficial effects on diabetes risk is that soy is a low glycemic food. Soy’s low glycemic index helps to keep blood glucose levels under control. This is especially important for people with diabetes. Many experts believe that a high carbohydrate diet is best for people with diabetes. However, carbohydrates can raise blood glucose to dangerous levels, which lead many medical professionals to recommend a low carbohydrate diet. However, not all carbohydrates act the same. Some are quickly broken down in the intestine causing the blood glucose levels to rise rapidly. These types of carbohydrates are said to have a high glycemic index. Others, like soy, are broken down more slowly and have a low glycemic index. By consuming soy foods, a patient can get the value of carbohydrates and keep blood glucose under control. Table 1 shows the glycemic index of a variety of soy food products from Revival Soy.

Another advantage of low glycemic foods is that they prevent the spikes in blood sugar often observed with high glycemic foods. These blood sugar spikes cause food cravings and often result in binge eating that destroys so many diets. The consumption of low glycemic foods is becoming recognized as a smart way to eat since it helps with weight loss and is particularly helpful to diabetics for controlling blood sugar levels.

In addition to potential direct beneficial effects of soy on diabetes, adding soy to the diet may also provide health benefits for conditions associated with diabetes, including nephropathy, CHD, and weight loss. Soy can help improve kidney function in diabetes patients with nephropathy. Azadkbakht et al. (2003) conducted a study among 14 women and men and concluded that soy can modify the risk factors of heart disease and improve kidney function in patients with type II diabetes. A study conducted by Teixeira et al. (2004) found that isolated soy protein consumption improves several markers that may be beneficial for type 2 diabetic men with nephropathy.

Table 1. The Glycemic Index of Revival Soy products
Glycemic Index
Product, Carbohydrates (grams), Value, Category*
Chocolate Splenda Shake 34 25 Low
Choclolate Fructose Shake 36 33 Low
Chocolate Raspberry Bar 33 (6 net) 47 Low
Peanut Chocolate Pal Bar 31 52 Low
Soy Spaghetti (boiled) 34 47 Low
*Glycemic Index Categories: <55 = Low Glycemic Food; 56-69 = Medium GI Food; >70 = High Glycemic Goods

Soy works to improve serum lipids and has other cardiovascular benefits. Studies have demonstrated that adding soy to the diet can lower total cholesterol and lower LDL cholesterol (Anderson et al., 1995). In addition soy has been shown to improve arterial compliance (Nestel et al., 1997) and modify LDL oxidation (Wiseman et al., 2000)

Recent clinical trials have begun to describe the weight loss benefits of soy protein (Allison et al., 2003; Fontaine et al., 2003; Goodman-Gruen and Kritz-Silverstein, 2003; Deibert et al., 2004). While the exact mechanism of action is not clear there is preliminary work that suggests that genistein reduces adipose deposition in mice (Naaz et al., 2003). It has also been reported that genistein effects lipid metabolism and adipocyte proliferation (Nogowski et al., 1998; Harmon and Harp, 2001). Finally, soy protein may work to suppress food intake and gastric emptying through the ?-conglycinin peptone (Nishi et al., 2003).


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