Best Food Facts received a reader question asking, "Does eating soy negatively impact our health?" To answer this question, we reached out to Barbara Klein, PhD, Professor Emerita of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign.
Dr. Barbara Klein:
Soy foods have been part of the diet in many countries, particularly in China, Korea and Japan, for centuries. The types of whole soy foods used include edamame (green soybeans), tofu (many different types), and fermented foods (e.g. soy sauce, miso, tempeh). Traditional Asian diets typically have 20-30 grams of soy per day, while Westerners consume much less, at about 1-5 grams daily. The difference is that in the U.S. and other Western nations, whole soy foods are consumed but in lower amounts than in Asian countries. However, processed soy (textured soy) and ingredients (soy protein concentrates and isolates) appear in many commercial food products, often meat and dairy protein substitutes, but also in baked goods, salad dressings and baby formulas. This has raised questions about soy allergy and plant phytoestrogens (compounds called isoflavones that are similar in structure to estrogen) and their effects.
In the scientific literature, there are hundreds of studies about soy and its effects in animal systems (usually mice or rats). These studies review everything from growth rates to cancer protection to osteoporosis. Given the number of studies, there are both negative and positive findings. The preponderance of evidence is that whole soy foods, those usually used in Asian diets, have positive effects on health. Investigations of individual components of soy have resulted in mixed findings, due to differences in methodologies, subjects, amounts administered and outcomes measured. Controlled human studies are difficult to do and rare.
Based on population studies of large groups of people and human studies, the consensus of medical and nutritional professionals studying and assessing soy’s benefits and risks is that moderate intake of soy foods, primarily whole soy products, is beneficial in lowering the risk of many diseases—coronary heart disease, breast and prostate cancer, and osteoporosis. Based on animal studies, use of soy supplements with high concentrations of isoflavones, may be less beneficial.
If you like soy foods, especially the traditional ones, continue to eat them, knowing that they have high quality protein, vitamins and minerals, and compounds that promote human health and reduce risk of diseases.
For more information about soy, check out the fully-referenced technical fact sheets from the health and nutrition experts at SoyConnection.com.
Do you have a food question to ask the experts? Submit a question here!
Who determines what’s for dinner at your house?