Nutritional Pearls: Soybeans, Legumes, and Type 2 Diabetes

Rachel is a 28-year-old woman who struggles with her weight and who follows a vegetarian diet. Rachel is concerned about her risk of diabetes and asks if there are any healthy sources of protein that may also help her lower her risk of developing the disease.

How would you advise your patient?
(Answer and discussion on next page)

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Answer: Soybean consumption could help to lower the risk of developing type 2 diabetes.

It's true that legumes, which include black beans, great northern beans, soybeans, green beans, and okra, can help you improve your cholesterol scores and your blood pressure as well as reduce your risk of heart disease. Soybeans have been of particular interest because they are an important source of protein in large portions of the world's population. Consuming soybeans and processed soy has been linked with improvements in the elements of metabolic syndrome, and while there's been some concern that the phytoestrogens that soybeans contain might increase the risk of breast cancer, the best research we have now indicates that eating more soy might actually reduce your risk of breast cancer.

The Research

Today’s research looks at soy intake and diabetes. Researchers in China recruited nearly 65,000 Chinese women between the ages of 40 and 70 who lived in 7 urban areas in Shanghai, China, to participate in the prospective study. At the start of the study, trained interviewers administered detailed dietary, health, and demographic questionnaires and measured height, weight, and waist and hip circumferences. Women who had been diagnosed with diabetes, heart disease, or cancers were excluded from participation.
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Two years later, the participants were visited again, and dietary and health questionnaires were again administered, noting if any of the women had been diagnosed with type 2 diabetes in the interim. After another 2 years, the authors again noted any women who had been diagnosed with type 2 diabetes in the intervening period, and the study ended.

The authors analyzed the participants' intake of legumes in general and soybeans and soy products in particular and grouped that intake into 5 increasing levels of consumption. They then compared the diets of those who developed type 2 diabetes with those who did not, after taking into account such variables as body mass index, waist to hip ratio, physical activity, vegetable intake, total caloric intake, education, smoking status, and menopausal status.

The Results

Compared with those who ate the least legumes (including soybeans and peanuts), those who ate the most legumes were 38% less likely to develop type 2 diabetes. Soybeans alone seemed to be more powerful, however: Those who ate the most soybeans were 47% less likely to develop diabetes than those who ate the least soybeans, while those who ate the most soy protein were only 12% less likely to develop diabetes than those who consumed the least soy protein. Interestingly, those in the second quintile of intake of soy protein were 25% less likely to develop diabetes than those who ate the least—suggesting that it's the soybeans as a whole, and not just the soy protein they contain, that is what we might call the active ingredient.

What's the "Take-Home"?

The average Westerner is unlikely to consume as much soy as those who live in Asian countries. That said, it's clear that soybeans (also known as edamame) are great for you—but so are other legumes.

Reference:
Villegas R, Gao Y-T, Yang G, et al. Legume and soy food intake and the incidence of type 2 diabetes in the Shanghai Women's Health Study. Am J Clin Nutr. 2008;87(1):162-167.