Can soy intake decrease sperm count, delay puberty or decrease size of sexual organs?
Researchers presenting in Tokyo reported on two studies that assessed the impact of soy intake on both sperm and semen parameters. In one crossover study conducted on 32 healthy young men consuming diets in random order supplemented with milk protein isolate, low-isoflavone isolated soy protein or high-isoflavone soy protein, no significant effect of diet on semen parameters was observed, including semen volume, sperm concentration, sperm count, total motile sperm count, sperm motility or sperm morphology. In the second study, 20 volunteers were randomized to receive different levels of isoflavones for 3 months. When compared to baseline, there were no statistically significant differences in ejaculate volume, sperm concentration, count and motility of spermatozoa in men given isoflavones (Messina, 2009). In addition, three intervention studies with men consuming 40-70 mg/day of soy isoflavones from soy foods or soy supplements failed to show effects on plasma hormones or semen quality
