Soy Products can reduce men's Sperm Counts

Soy products reduce men's sperm counts, especially if they are obese
Source: Human Reproduction 2008; Advance online publication
Researchers correlate intake of soy products and sperm counts among men seeking assessment for infertility.

MedWire News: Eating a lot of soy products appears to lower men's sperm counts, research suggests.

US researchers asked 99 men who attended a fertility clinic to be assessed for subfertility how often they ate soy products over the previous 3 months, and the size of the serving.

Jorge Chavarro (Harvard School of Public Health, Boston, Massachusetts, USA) and colleagues found that men who ate the most soy had 41 million sperm/ml less than the other men. "Normal" sperm concentrations range from 80 to 120 million sperm/ml.

"Men in the highest intake group had a mean soy food intake of half a serving a day: in terms of their isoflavone content that is comparable to having one cup of soy milk or one serving of tofu, tempeh or soy burgers each other day," the researchers explain.

Soy intake was more strongly associated with reduced sperm counts in men who were overweight or obese than those with a healthy weight, the team notes.

High intake of isoflavones-a type of phytoestrogen-have been related to decreased fertility in animal studies, but not previously in humans.

Chavarro et al suggest that the estrogenic activity of soy products may impair sperm production by interfering with other hormonal signals.

This would be consistent with the finding that sperm counts were reduced further in overweight men, whose high levels of body fat produce more estrogen than their slimmer counterparts.