Soy Foods, Sperm Concentration Link?
Study Links Soy Foods to Lower Sperm Concentration; Soy Foods Industry Critical of Study
July 23, 2008 -- Men who eat a lot of soy foods may have a lower sperm concentration than men who don't eat soy foods, according to a new study.
But the study, published online in Human Reproduction, doesn't claim that soy foods are to blame for those lower sperm concentrations, most of which were still in the normal range. Meanwhile, the soy foods industry is drawing attention to the study's limits.
The study's data came from 99 men who visited the Massachusetts General Hospital Fertility Center with their partners between 2000 and 2006.
The men submitted semen samples and completed a questionnaire that included a question about how often they had eaten 15 different soy foods (such as tofu, soy milk, soy burgers, and edamame) and how much of those foods they ate in the previous three months.
Almost all of the men -- 90% -- had sperm concentrations that were within the normal range, and 42% of the men had normal semen analyses, which include sperm shape and motion in addition to sperm concentration.
Most of the men -- 39 of them -- said they hadn't eaten any soy foods during the previous three months. Another 18 men said they ate soy foods less than twice a month, 22 said they ate soy foods between twice a month and twice a week, and 20 said they ate soy foods at least twice a week.
Men who ate soy foods tended to have lower (but still normal, in most cases) sperm concentrations than men who ate no soy foods. That was especially true of overweight and obese men.
Soy foods weren't associated with any other aspects of the semen analyses, such as sperm's shape or movement.
Since the study was a snapshot in time, it doesn't prove that eating soy foods affected the men's sperm concentration; the researchers note that other factors -- including being overweight or obese -- could have been involved. And the men who took part in the study may not be representative of all men.
"The clinical significance of these findings remains to be determined," write the researchers, who included Jorge Chavarro, MD, ScD, ScM, of Harvard School of Public Health's nutrition department.