As a former vegetarian, I’ve consumed more than my fair share of soy products. And I’m not alone: Vegans, health nuts, and the lactose intolerant alike have welcomed soy as an easy, cheap, and tasty way to get enough protein without the help of meat or dairy. But could this soy craze be bad for our health? Research suggests soy might mess with that essential hormone balance and derail physical development.
Soy Bad — Why It’s Dangerous
Soy isn’t just for the veg-heads among us — in fact, it’s everywhere, in many supermarket products (by some estimates up to 70 percent!). Whether such high levels are safe for consumers is hotly debated. The issue stems from soy’s phytoestrogens, compounds that mimic estrogen in the body. There’s conflicting research on the effects of phytoestrogens, but evidence is serious enough that the American Heart Association issued a warning against the use of soy supplements in food or pills. So what’re the major fears?
In men, soy has been shown to lower testosterone levels and sex drive, slow down sperm and lower sperm counts, and hamper erectile function (though only when consumed in huge quantities) Soy, phyto-oestrogens and male reproductive function: a review. Cederroth, CR, Auger, J., Zimmermann, C., et al. Department of Genetic Medicine and Development, University of Geneva Medical School, Switzerland. International Journal of Andrology, 2010 Apr;33(2):304-16 Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic. Chavarro, J., Toth, T., Sadio, S., et al. Human Reproduction, 2008 November; 23(11): 2584–2590 Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Messina, M. Department of Nutrition, School of Public Health, Loma Linda University, California. Fertility and Sterility, 2010 May 1;93(7):2095-104.
Women aren’t immune either: Soy consumption might mess with menstrual cycles, decrease fertility, and increase the risk for breast cancer (though cancer research is mixed — in fact, soy might help some women with breast cancer and might be a serious risk for others; it all comes down to the type of breast cancer a woman has) Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis. Hooper, L., Ryder, JJ, Kurzer, MS, et al. School of Medicine, Health Policy and Practice, University of East Anglia, Norwich. Human Reproduction Update, 2009 Jul-Aug;15(4):423-40 Effects of soy phytoestrogens genistein and daidzein on breast cancer growth. De Lemos, ML. Provincial Systemic Therapy Program, British Columbia Cancer Agency, Canada. Annals of Pharmacotherapy, 2001 Sep;35(9):1118-21 Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of combined evidence from cohort studies of US and Chinese women. Nechuta, SJ, Caan, BJ, Chen, WY, et al. Division of Epidemiology, Department of Medicine, Vanderbilt University School of Medicine. American Journal of Clinical Nutrition, 2012 Jul;96(1):123-32. Epub 2012 May 30. In younger girls, soy might induce premature puberty Soy isoflavones and human health: breast cancer and puberty timing. Valladares, L., Garrido, A., Sierralta, W. Laboratorio de Nutricion y Regulacion Metabolica. Instituto de Nutricion y Tecnologia de los Alimentos. University of Chile. Revista Medica de Chile, 2012 Apr;140(4):512-6.
In both genders, soy can interfere with the endocrine system, which regulates mood, growth, and development, and the thyroid, which helps the body use energy and ensures proper functioning of the brain, heart, muscles, and other organs Soy as an endocrine disruptor: cause for caution? Bar-El, DS and Reifen, R. School of Nutritional Sciences, The Hebrew University of Jerusalem, Israel. Journal of Pediatric Endocrinology and Metabolism, 2010 Sep;23(9):855-61 Unawareness of the Effects of Soy Intake on the Management of Congenital Hypothyroidism. Fruzza, AG, Demeterco-Berggren, C., Jones, KL. Division of Endocrinology, Department of Pediatrics, University of California San Diego. Pediatrics, 2012 Aug 20. And despite big claims, soy isn’t the best muscle fuel; it’s less effective than whey or milk protein when it comes to muscle protein synthesis.
Soy, Much Better — Your Action Plan
Whether soy is awesome or dangerous might come down to how much and what kinds of soy a person consumes Factors to consider in the association between soy isoflavone intake and breast cancer risk. Nagata, C. Department of Epidemiology & Preventive Medicine, Gifu University Graduate School of Medicine, Japan. Journal of Epidemiology, 2010;20(2):83-9. Genetically modified soy consumption in particular has shown devastating results in animal-based studies, including severely reduced fertility, slower growth, higher mortality, and (brace yourself) testicles that changed from pink in color to dark blue (granted, these results were in mice) Ultrastructural analysis of testes from mice fed on genetically modified soybean. Vecchio, L., Cisterna, B., Malatesta, M., et al. European Journal of Histochemistry, Oct 2004:48(4);448-454. But back in the human world, traditionally fermented soy products (think tofu or tempeh) seem to be healthy for humans in reasonable quantities.
Love that tofu? Good news is you probably don’t have to give up soy completely Soy isoflavones: a safety review. Munro, IC, Harwood, M., Hlywka, JJ, et al. CANTOX Health Sciences International. Nutrition Reviews, 2003 Jan;61(1):1-33. Just follow these guidelines to minimize any potential harm.
- Avoid highly processed soy products. Read labels. Beware of protein bars and fake meat, and stick to whole soy foods, like edamame and tofu.
- Stick to fermented. Fermentation reduces the level of phytoestrogens in soy by as much as a third. Fermented products include soy sauce, miso, tempeh, and (for the more daring among us) natto.
- Avoid fast foods. As if we needed another reason: Fast food is a common source of hidden soy ingredients, meaning regular fast food consumption equals regular consumption of large quantities of soy.
- Get enough iodine. Eating the RDA of iodine (150mcg) should prevent any thyroid problems that might otherwise result from munching down on too much soy Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Messina, M., Redmond, G. Department of Nutrition, School of Public Health, Loma Linda University, California. Thyroid, 2006 Mar;16(3):249-58. Good sources include cod, shrimp, tuna, milk, baked potatoes, and seaweed.
- Diversify your diet. Whether you’re animal-free or as carnivorous as they come, choosing variety instead of the same old soy-laden products is good for your health.
Are you a die-hard soy devotee, or just a little skeptical? Tell us in the comments below, or tweet the author @LauraNewc.