Flavonoids (Soy)Pregnancy

Negative effect of soy on sperm

Researchers from the Harvard School of Public Health in Boston tell us eating (a lot) more soy food results in lower sperm counts.

First, the details.

  • 99 male partners of subfertile couples were studied to determine the association of soy foods and isoflavones intake with semen.
  • The intake of 15 soy-based foods during the previous 3 months was recorded.

And, the results.

  • Greater intake of soy food was associated with lower sperm concentrations.
  • This relationship was not affected by age, abstinence time, body mass index, caffeine and alcohol intake, and smoking.
  • Men in the highest level of soy food intake had 41 million sperm/mL less than men who did not consume soy foods — a significant difference.
  • Results for individual soy isoflavones were similar to the results with soy foods, and were strongest (but not statistically significant) for glycitein.
    • Glyciten accounts for 5% to 10% of the total isoflavones in soy food products.
  • The inverse relation between soy food intake and sperm concentration was more pronounced in men with the highest soy food intake and among overweight or obese men.
  • Soy food and soy isoflavone intake were unrelated to sperm motility, sperm morphology, or ejaculate volume.

The bottom line?
The authors make the obvious conclusion, “Higher intake of soy foods and soy isoflavones is associated with lower sperm concentration.”

But the significance of these findings (aside from the intuitive conclusion) on the ability to impregnate a female remains to be documented. We don’t know if the inability of these subfertile couples to conceive was a direct result of the men’s soy diet. Afterall, they were all subfertile regardless of the soy intake.

But I’ll bet they’ll be eating a lot less edamame.

The authors discuss other studies in this field. Apparently, one study found no effect and another reported a positive effect of high soy intake on sperm.

7/25/08 09:35 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at www.Vicus.com, a complementary and alternative medicine website.