In the last 50 years, soy production has grown tenfold from 27 to 269 million tonnes.
The rise of soy can be attributed to the perceived health benefits of the bean, however, it is a controversial topic with strongly conflicting opinions. Search soy on the internet and you’ll find that it has positive and negative effects on thyroid activity, heart health, testosterone, and breast cancer.
In terms of nutritional content, soybeans contain uniquely high levels of protein and fat, and anti-nutrients which impair the digestion and absorption of proteins and macronutrients. Thankfully, those anti-nutrients are vulnerable to the processing methods used in the production of soy foods, limiting their effect.
Soybeans also contain bioactive compounds, notably isoflavones and phytosterols. Isoflavones are believed to be responsible for some of soy’s health effects due to the estrogenic effect on the body. Unfortunately, the isoflavone content of each type of soy food varies greatly, which makes it difficult to ascertain one’s intake level. The amount of isoflavone you need to consume to experience health benefits depends on the composition of your bacterial flora, however we would recommend between 25-50 mg/day, the average intake in Japan, where soy is regularly consumed.
When it comes to health effects, soy does not appear to affect thyroid activity in humans. In terms of heart health, Soy-protein supplementation benefits LDL-C levels, blood pressure, and endothelial function, but only slightly, so the benefit to your health is uncertain.
In men, regular intake of soy protein may reduce the risk of developing prostate cancer. Soy protein also has the potential to reduce testosterone levels and interfere with fertility, but only when consumed in excess — no such effects have been observed from the daily consumption of 10–70 grams of soy protein or 60–240 mg of isoflavones. (THIS IS VERY IMPORTANT).
In women, soy-protein intake is associated with a reduced risk of breast-cancer incidence and mortality.
To conclude, criticism of the soybean is overblown. While it may not have all the benefits that others claim, if consumed in the right amounts it can have a positive impact on health.