Question: Will eating soy foods lower a man's sperm counts and affect his fertility?
Answer: This is a great question, this is really -- I don't want to say controversial -- but it's a big unknown.
The Arbor Clinical Review for Nutrition just came out with three studies and a review looking at this very question. There's isoflavones in soy and phytoestrogens in soy that act as weak estrogen molecules in the body, and there's been some concern and question whether this can affect sperm count and production, which is dependant on testosterone. So there have been some interesting studies.
Some veterinarians taking care of cheetahs in captivity, noting that they had difficulty with their reproduction found that they had a soy diet and pulled them off the soy diet and then noted an increase in FSH and LH -- those are hormones that are precursors testosterone, which is helpful for sperm production.
So finally, soy intake in the form of edamame, soy nuts, soybeans, soy milk, tempeh and tofu, in one to two servings per day is very healthy, it's probably very preventative against prostate cancer, but if a man has a low sperm count and he comes in, I'll certainly do counseling and do a dietary intake and remove soy for a period of one to two months to see if that's helpful. But generally, soy is a very healthy whole-protein plant food source.