Harvard Men's Health Watch

Medical memo: Soy and sperm

Soy has come a long way. Once considered an obscure and inscrutable staple of the far-off Asian diet, it became an icon of American counterculture in the 1960s and '70s, then a prized health food in the decades that followed. Soy has been touted as lowering cholesterol, reducing the risk of heart disease, and protecting the prostate. But studies of these possible benefits have had mixed results at best, and a report from Harvard raises the possibility that dietary soy may lower sperm counts.

The study

The soy study was part of a long-term investigation of environmental factors and fertility. The subjects were 99 male partners of sub-fertile couples. Each man had a medical evaluation and complete semen analysis, and each provided a detailed three-month dietary history that evaluated 15 soy-based foods, ranging from tofu and tempeh to soy milk, veggie burgers, and "energy bars" containing soy protein.

The study found that the men who consumed the most soy had the lowest sperm counts. And it didn't take much soy to do the trick — as little as one portion every other day was linked to a reduction in sperm count. All in all, the men who ate the most soy had counts that averaged 41 million fewer sperm per cubic milliliter than men who ate the least. The impact was greatest in overweight men, and the results remained valid after age, smoking, alcohol, caffeine, body mass index, and the time between specimen collection and the preceding ejaculation were taken into account.

To continue reading this article, you must login.
  • Research health conditions
  • Check your symptoms
  • Prepare for a doctor's visit or test
  • Find the best treatments and procedures for you
  • Explore options for better nutrition and exercise
Learn more about the many benefits and features of joining Harvard Health Online »