I get asked a lot whether or not soybeans and soy products, such as tofu and tempeh, are good for you. And it’s easy to see why there’s so much confusion on this topic, as many of the headline messages we see in the media are very conflicting. Some hail tofu as some kind of superfood, while after reading others you might expect to grow a third eye. So, I thought I would bring you the best quality and most up-to-date scientific evidence on the health topics surrounding soy.
Soy and hormones in men
The top concern I hear about from men is whether soy can affect male hormone levels. There have in the past been concerns about oestrogen-like activities of the isoflavones found in soy decreasing testosterone levels in men. However, the basis of these claims stems from early studies in rodents (1), but it has been shown that rodents metabolise isoflavones differently to humans. In fact, a recent meta-analysis – the best form of scientific evidence – combined the results from 15 human clinical trials, and concluded that soy foods do not alter testosterone levels in men (2). (See my article about which kinds of evidence to believe). Even at higher than average rates of consumption (higher than is even typical among some Asian cultures), there is also no evidence that soy isoflavones affect circulating oestrogen levels in men (3). This does all kind of make sense… the hundreds of millions of men in Asian cultures who frequently eat soy products are not infertile or growing man boobs. In fact, there is reason to believe that soy is one of the reasons why the Japanese, among the biggest soy eating countries in the world, is also one of the healthiest nations. This brings me on to the health benefits of soy:
Soy is an excellent source of protein
Soybeans are a complete protein, meaning they provide all the essential amino acids (the ones we have to get from our food because we can’t make them in our body). A cup of cooked soy beans contains a whopping 22g protein, a 100g serving of tempeh has 19g, and a 100g serving of tofu contains 13g.
Soy could be protective against breast cancer in women
This has been a topic of debate in the past but recent meta-analyses, which analyse loads of clinical trials, show that soy consumption could in fact be associated with reduced risk of breast cancer incidence (4, 5).
Soy can replace foods that are bad for you
As mentioned, soy provides an excellent source of protein, and all without the cholesterol and saturated fat levels found in most red meats. So if you swap a pork sausage hot dog for a soy-based alternative, you are avoiding processed meat, which has been classified by the International Agency for Research on Cancer as a carcinogen (cancer causing) (6). If you are instead replacing it with a high protein, low fat, high vitamin and mineral based food like tofu, there are significant advantages for your health.
The downsides of soy products
Soy products that have been processed to resemble the shape of a chicken nugget or the taste of a bacon rasher require quite a bit of processing, and the ingredients list can look worryingly long. There is often added salt and fat in anything that has been battered, and other flavourings and colourings in mock-meat style products to give it a meaty flavour. As with any foods, the less processing the better. For this reason, simple tofu is much better than the heavily processed imitation meats. Better still, tempeh is a soy product made by simply fermenting cooked soybeans, so is even less processed than tofu, and contains more protein too. It also has a denser texture, so while it has been around for ages, 2018 is looking like the year it will finally outshine tofu as a great alternative to meat for vegans and meat-eaters alike!
1. K.S. Weber, K.D. Setchell, D.M. Stocco, E.D. Lephart (2001). Dietary soy-phytoestrogens decrease testosterone levels and prostate weight without altering LH, prostate 5alpha-reductase or testicular steroidogenic acute regulatory peptide levels in adult male Sprague-Dawley rats. J Endocrinol, 170 (2001), pp. 591–599
2. Niederberger, C. (2011). Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: Results of a meta-analysis. Journal of Urology, 185(2), 638.
3. Messina, M. (2010). Soybean isoflavone exposure does not have feminizing effects on men: A critical examination of the clinical evidence. Fertility and Sterility, 93(7), 2095-2104.
4. Fritz, H., Seely, D., Flower, G., Skidmore, B., Fernandes, R., Vadeboncoeur, S., . . . Shioda, T. (2013). Soy, Red Clover, and Isoflavones and Breast Cancer: A Systematic Review (Isoflavones and Breast Cancer). 8(11), E81968.
5. Xie, Q. L., Chen, M. Y., Qin, Y. X., Zhang, Q. T., Xu, H. D., Zhou, Y., . . . Zhu, J. (2013). Isoflavone consumption and risk of breast cancer: A dose-response meta-analysis of observational studies. Asia Pacific Journal of Clinical Nutrition, 22(1), 118-127.
6. Cancer.org (2015). World Health Organisation Says Processed Meat Causes Cancer. Accessed at: http://www.cancer.org/cancer/news/world-health-organization-says-processed-meat-causes-cancer