Soy comes in a variety of forms, from soy milk, to tofu, to whole soy beans; the options are endless! It has been a staple in Asian countries for centuries, consumed in all its forms. However, soy has become a controversial topic in recent times, with some schools of thought emerging that suggest soy may not be as healthy as we once thought…
Why is this? Well, soy contains isoflavones, which are a class of phytoestrogens (oestrogen-like chemicals), thought to act in a similar way to oestrogen in the body1. These compounds aren’t unique to soy. In fact, they are in most beans and legumes, but the concentration in which they are found in soy is a lot higher than other sources. Phytoestrogens compete with oestrogen to bind to and activate oestrogen receptor sites1. However, the oestrogenic activity of phytoestrogens is far weaker than that of human oestrogen2. Indeed, it is suggested that this can be beneficial in the context of breast cancer, as a woman’s risk of developing it can be linked to lifetime exposure to oestrogen2. When a woman has children under the age of 30, breastfeeds, has her first period over the age of 12, and does not undergo early menopause, her exposure to oestrogen is decreased or interrupted, reducing her lifetime exposure and therefore overall breast cancer risk2.
Men often voice concerns that soy will increase their risk of developing prostate cancer and alter their body composition. A large review of multiple studies found neither to be true1. However, it was identified that men who consumed significant amounts of miso soup had a slightly higher risk of developing stomach cancer, although the correlation appears to be dose-dependent (I.e., the more you eat, the higher your risk)2. In terms of the purported effects of soy on testosterone and body composition, a 2010 meta-analysis found that soy did not alter the body composition or testosterone levels of men3. Therefore, encourage the men in your life to eat soy!
It is important when considering what the literature tells us that the body of evidence is considered as a whole, providing a general consensus, rather than single studies in isolation, which can facilitate fear-mongering. Dr. Tim Crowe, a career nutrition research scientist summarised the evidence around soy here, essentially concluding that soy can be included as part of a healthy diet for most people. He asserts that if you trawl the internet hard enough, you will find evidence to infer that most foods can cause harm, even humble broccoli!
Generally, it is advised that moderate consumption of soy should not lead to any increase in cancer risk and can be an excellent way to reduce saturated fat intake when substituting for meat2. So, it’s best to just view soy as another food! So, enjoy your tofu, soy milk and soy beans as you please, in moderate amounts as is advised with all foods.
References:
- Li N, Wu X, Zhuang W, Xia L, Chen Y, Zhao R et al. Soy and Isoflavone Consumption and Multiple Health Outcomes: Umbrella Review of Systematic Reviews and Meta‐Analyses of Observational Studies and Randomized Trials in Humans. Molecular Nutrition & Food Research. 2019;64(4):1900751.
- Crowe T. The science of soy: health, harms and hyperbole - Thinking Nutrition [Internet]. Thinking Nutrition. 2020 [cited 29 October 2020]. Available from: https://www.thinkingnutrition.com.au/soy-health-harms-hyperbole/
- Hamilton-Reeves, J. M., Vazquez, G., Duval, S. J., Phipps, W. R., Kurzer, M. S., & Messina, M. J.. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: Results of a meta-analysis. Fertility and Sterility. 2010;94(3), 997–1007. https://doi.org/10.1016/j.fertnstert.2009.04.038