There are many persistent myths surrounding the consumption of soy. One of them is that soy can ‘feminise’ men because it contains estrogen. In addition, many women have been warned about consuming soy because of the estrogen it contains. I will, first of all, explain the origin of this myth and then go on to show why it is not supported by any of the available evidence. This anti-soy propaganda has been fuelled by the Weston A. Price Foundation (an organisation which advocates the health benefits of animal-based fats and opposes vegetarian and vegan diets). Interestingly, many studies actually suggest that soy has a number of health benefits.
The myth that soy can ‘feminise’ men most likely has its basis in flawed animal intervention experiments. In these experiments, animals were injected with isolated isoflavones (a class of phytoestrogens – plant estrogens – found predominantly in in legumes and beans). It is important to point out first of all that plants do not contain estrogen, but phytoestrogen; a point of confusion which probably contributes to the misconception that consumption of soy will give you ‘man boobs’. Secondly, with these animal intervention studies, there is a difference between studying the effects of soy isoflavones in isolation compared to the effects of whole soy foods when consumed.
Jay Kaplan, head of comparative medicine at Wake Forest University School of Medicine, argues:
I’m reasonably sure that any time you take one of those isoflavones and give it separately, you don’t see the same effects as when all three of the isoflavones of soy are given.
Indeed, many nutritionists argue that the effects of an isolated vitamin are different compared to the effects of a whole food which contains that vitamin, along with many others. This would partly explain why the animal studies result in negative health effects, whilst epidemiological studies of Asian populations – who eat whole soy foods – do not show signs of negative health effects. In fact, quite the opposite is suggested in these population studies; a point I will elaborate on later.
The third issue with these animal intervention studies is that phytoestrogens behave differently in different species, so the effects of these isoflavones on animals may bear no relevance to humans whatsoever. The fourth issue with these studies is that they involve exposing animals to phytoestrogen levels many times higher than those absorbed by humans through eating whole soy foods. And finally, the fifth issue with these studies is that they involve injecting the animal with the isolated isoflavones, which means that the compounds bypass the usual metabolic pathways.
It has been established that soy isoflavones and other phytoestrogens can bind to estrogen receptors, mimicking the effects of estrogen in some tissues, while blocking the effects of estrogen in others. There is no evidence that mimicking the effects of estrogen in some tissues has negative health effects in humans. A meta-analysis of 15 studies on the effects of soy isoflavones on male hormones, carried out by the University of Minnesota, found no evidence of significant effects. Testosterone levels remained healthy. Low levels of testosterone in men can lead to depressed mood, loss of muscle mass, weight gain and erectile dysfunction – however, there is no evidence that the consumption of soy results in anywhere near such low levels of testosterone.
The authors of this meta-analysis also noted that for all of the studies they examined, soy protein and isoflavone intake “greatly exceeded” typical Japanese dietary intake. Moreover, the authors criticised those studies which did find decreases in levels of testosterone, due to their flawed methodology. One study, for example, included only 12 subjects, had no control group and did not describe the method used to assess hormone levels. Therefore, men shouldn’t worry that consuming soy will take their manhood away.
What men (and women) should be worried about are the high levels of female sex hormones (progesterone and estrogen) contained in milk, not to mention quantities of growth hormones as well. Evidence suggests that dairy products are closely correlated with the incidence of testicular and prostate cancer, as this study points out. This could be related to the levels of female sex hormones present in dairy products. These hormones may also be related to the high incidence of breast cancer in the West. That said, more research needs to be done in order to confirm this.
Many nutritionists have become interested in the health benefits of soy. Epidemiological studies show that the significantly higher levels of soy consumed by Asian populations do not result in low testosterone for men or fertility problems for women. In fact, populations that consume a lot of soy, particularly those in eastern Asia, have less breast cancer (a hormone-dependent cancer), prostate cancer (also a hormone-dependent cancer) and cardiovascular disease. The fact that soy can lead to a lower incidence of hormone-dependent cancers may be down to the way in which soy isoflavones can block the effects of estrogen in some tissues. However, more research needs to be done in this area. Additionally, women in Asian populations report fewer menopausal symptoms, while both men and women have a lower incidence of osteoporosis and ageing-related brain diseases.
On the other hand, we must also bear in mind that many lifestyle factors can lead to this lower incidence of various diseases. In The China Study, for example, the authors argue that it is the lower consumption of animal products which result in this lower incidence of various diseases. However, other lifestyle factors may be at play, such as lower rates of drinking, smoking and other harmful lifestyle choices. That said, diet is probably the most significant difference between Asian and Western populations. When Asians emigrate to Western nations such as the US and adopt the American diet, their disease rates change. As Professor Kaplan explains:
It does seem to be something that’s in the environment, and it looks like this reliance on plant proteins is one of these things that go away after [immigrants have] been here a while…What also goes away is any protection from chronic disease that we ascribe to those populations.
It is entirely feasible that these health benefits can be attributed to soy consumption. Many clinical and epidemiological studies point to the disease-preventing properties of soy consumption. Soy-based infant formulas have so far proved to be completely safe, with no adverse effects observed in infants fed a soy-based infant formula compared to those fed a cow’s milk-based infant formula. This contradicts claims made by Sally Fallon (co-founder of the Weston A. Price Foundation) who criticises soy-based infant formulas and wants them banned. A high intake of soy isoflavones has not been shown to create significant changes in thyroid hormone levels. The soybean is high in protein and is rich in micronutrients such as calcium, iron, magnesium, potassium, various B vitamins, vitamin C and zinc. Fiber and omega-3 fatty acids are also present. Soy can therefore easily be incorporated into a healthy diet.
The only worry people should have about soy is if they have an allergy to it. A sign that you might have an allergy to soy is if when you consume soy products, you get an itchy mouth or throat, or an outbreak of acne. If you have a mild allergy to soy this may only happen when you consume large quantities of soy products; soy consumption in moderation is unlikely to cause any issues. The hormonal effects of soy are weak at best, so these are unlikely to be the cause of an outbreak of acne. Soy can actually be good for the skin (assuming you aren’t allergic to it) based on the micronutrients and fatty acids it contains.