The dangers of soy for men are a result of the high levels of the female hormone estrogen that soy and soy-based products contain. Primarily, soy affects the quality and concentration of a male’s sperm, especially if taken in large quantities or if the subject was exposed to high levels in the womb. A recent study at Harvard University showed that there was a definite correlation between men with low sperm counts and a high intake of soy foods. The study revealed that the average sperm concentration of 80 to 120 million per millimeter of an adult male was more than halved when soy formed part of the diet. The case is more compelling in the study of obese males whose sperm levels are even lower owing to the estrogen making properties of fat tissue.
Scientists believe that the isoflavones (daidzein, genistein and glycitein) found in soy is to blame for poor sperm concentrations. These isoflavones act like estrogen does and they therefore inhibit the production of sperm. Moreover, Professor Lynn Fraser of King's College London has also issued warnings about the isolflavone genistein which is believed can contribute to the failure of the sperm to fertilize the egg. However, these findings were founded on test-tube based experiments and soy industry bodies have countered that the genistein found in soy-based products reacts differently to the pure form of the isoflavones that was used to conduct the research.
Soy is found most abundantly in foods such as soya beans, tofu, tempeh, tofu or soy sausages, bacon, burgers, soy milk, cheese, yogurt, ice cream and nuts. However, soy and soy derivatives are to be found in approximately 70% of all foods and therefore reducing intake can be difficult. For example, pork pies, breakfast cereals, mayonnaise and margarines, sausages, lasagna, beef burgers and chicken nuggets are some of the foods that rely on soy as a source of cheap protein. The soy derivative lecithin is also pervasive in the bakery and confectionary industries because of its effectiveness as an emulsifier.
It should be noted that soy is very much a mainstay of Asian diets and no significant side-effects have been found in these countries. However, it is salutary to bear in mind that the Asian soy diet is based largely on fermented soy products, such as miso soup and tofu; the fermentation process is thought to destroy the chemicals that are considered harmful in the above experiments.