Are You Afraid of Soy?

Since I am not a vegetarian or vegan I cannot say that I am a big Soy fan but, as a Professor of Nutrition I can surely tell you that Soybeans are a wonderful source of health promoting phytochemicals.  These plant-derived compounds have biological activities that include protecting DNA and other cellular compounds from oxidative damage, driving the expression of health promoting proteins, and mimicking the activity of the body’s own hormones.

Asians living in Asia have been consuming a soy-rich diet for thousands of years and currently appear to derive many health benefits including lower incidence of heart disease and certain cancers, and Asian women suffer fewer menopausal symptoms.  The effects on the heart are thought to be linked to the ability of plant sterols to lower blood cholesterol although, this may also be due to reduced consumption of saturated fatty acids (Clin Nutr 91:32).  Soy foods also contain phytoestrogens which are related to human estrogen and thought to both mimic AND oppose its effects.  Epidemiological studies have shown better breast cancer survival rates of Chinese soy eaters but no effect or mixed results on US women (Nutr Rev 568:542; JAMA 302:2437).  In cell-based studies the phytoestrogen genistein was shown to accelerate the growth of breast cancer cells at low doses and inhibit growth at high doses (Anticancer Res 32:1181;  Nutr Rev 67:398).  Such in vitro studies clearly do not translate in vivo but these opposing actions should give pause to those considering taking soy as a supplement.  Also, the American Heart Association could not determine any consistent findings to demonstrate a relationship between soy consumption and menopausal symptom.

Another serious concern is allergic reaction to soy.  Allergic response to soy proteins is as common as those seen with milk, eggs, peanuts, tree nuts and shellfish but the reaction tends to be less severe (Am Soc Nutr Sci 134:1213S).  To facilitate digestion, soybeans, like all legumes should be thoroughly cooked.  Edamame is an immature soybean which is appealing because the young beans are easier to digest.  Tofu is a bean curd derived from soybeans, and fermented versions include soy sauce, soybean paste, natto, and tempeh, among others.  Soybeans are a common source of lecithin, a phospholipid used as an emulsifier in many processed condiments and packaged goods.  People with soy allergies should definitely read food labels as small quantities of soy proteins have been found in some soy lecithin preparations (Int Arch Allergy Immunol 126:218). 

Taken together, the observations and findings of soy-based diet outcomes suggest that soy is a healthy phytochemical that should be consumed in moderation.  However, it should be avoided completely if you are allergic.  For those of you concerned about genetically modified soy be sure to read the previous blog:  http://egglrock.blogspot.com/2014/09/what-you-need-to-know-about-gmo.html.