A study, published online in Human Reproduction, has found that statistically, men who eat a lot of food made from soy have a lower sperm count. The suspected reason is the presence, in nearly all soy-based foods, of some chemicals, isoflavones, which closely match female hormones.

The Harvard School of Public Health study has some limitations as it was retrospective and encompassed only 99 subjects, but the findings point that just one soy portion every two days leads to 41 million fewer sperm per milliliter of semen. The difference was significantly sharper in overweight men, whose fat tissue produces more estrogen.

Although, at least in obese and overweight men, there seems to be a negative effect of soy products on the sperm count, it is not the direct equivalent of reduced fertility. More important factors such as sperm quality are more relevant, as long as sperm count remains within the acceptable limits.

Soyfoods Association of North America has quickly issued a statement rebuffing the findings, and pointing out that the study observed an actual "watering down" of the sperm, which is caused by the increase of ejaculate volume. What this means is there are the same number of spermatozoa in a higher volume of fluid.

The soy bean, Glycine max, is an annual plant native to East Asia. Its seed is made up of 40 percent protein and around 20 percent oil. Overall, there is no actual proof that consuming soy decreases cancer risks. Its alleged health benefits are almost all subject to debate.