Does Soy Raise Estrogen Levels in Men?

Introduction

Soy is a high protein food from the soybean plant which has been eaten in Asian countries for centuries. There are a few different ways to consume soy. Soy milk is growing increasingly popular, tofu (made from soybean curds) and tempeh, which is fermented soybeans are all different forms of soy. There has been considerable concern over the years that soy could adversely affect estrogen levels in men. Soy contains phytoestrogens, which are similar to estrogen but exert weak estrogenic effects.

Is there any truth to the notion of soy raising estrogen levels in men? Read this article to find out.  

Soy and phytoestrogens

Phytoestrogens are compounds found in a variety of plant foods that may exert estrogen like effects. The two main phytoestrogen compounds are isoflavones and lignans ¹. Surprisingly, these phytoestrogens appear to have both estrogenic and anti-estrogenic properties. Phytoestrogens are the reason that many people believe soy intake could increase estrogen levels in men.  Phytoestrogens are not all bad however and there are many health benefits associated with phytoestrogens.

Health benefits of phytoestrogens

Animal studies and evidence from experiments suggest a role for phytoestrogens in the prevention of cancer, cardiovascular disease, osteoporosis and menopausal symptoms ¹.  Although experiments studying the effects of phytoestrogens in humans is limited, populations that tend to eat a lot of soy products often have lower rates of the aforementioned diseases.

Does soy have hormonal effects in men?

Soy and sperm quality

Does intake of soy isoflavones affect sperm quality in men? A study which gave 14 young men 40 mg/day of soy isoflavones found no negative effect of the soy supplement on sperm quality². After 2 months of daily soy supplementation researchers found no effect on testicular or ejaculate volume or sperm concentration, count or motility.

Does soy increase estrogen levels in men?

A study in older Japanese men that consumed soy daily found that as soy intake increased the  serum concentrations of estradiol decreased but also found soy intake had a small effect on levels of estrone³.

A few studies found that soy intake in men had no effect on estrogen levels in men. A study comparing older men assigned to eat meat or tofu for one month found no difference in estradiol levels at the end of the study ⁴. In another study men consuming 40 mg/day of soy isoflavones saw no changes in serum levels of estradiol at the conclusion of the study⁵.

It appears that soy intake does not affect sperm quality or estrogen levels in men. In fact, soy intake has been associated with a decreased risk of prostate cancer in men. In a future article I will discuss the link between soy intake and risk of prostate cancer in men.

Summary

• Soy has been safely consumed in Asian countries for centuries.
• Soy contains phytoestrogens, which may exert weak estrogenic effects in humans.
• The phytoestrogens in soy have been linked to prevention of cancer, cardiovascular disease, and osteoporosis.
• A study giving young men soy isoflavones found no effect on sperm quality.
• The few human studies testing the effects of soy intake on estrogen levels found that soy had little to no effect on estradiol levels in men.

Sources

1. Tham, D. M., Gardner, C. D., & Haskell, W. L. (1998). Potential health benefits of dietary phytoestrogens: a review of the clinical, epidemiological, and mechanistic evidence. The Journal of Clinical Endocrinology & Metabolism, 83(7), 2223-2235.
2. Mitchell, J. H., Cawood, E., Kinniburgh, D., Provan, A., Collins, A. R., & Irvine, D. S. (2001). Effect of a phytoestrogen food supplement on reproductive health in normal males. Clinical science, 100(6), 613-618.
3. Nagata, C., Inaba, S., Kawakami, N., Kakizoe, T., & Shimizu, H. (2000). Inverse association of soy product intake with serum androgen and estrogen concentrations in Japanese men. Nutrition and cancer, 36(1), 14-18.
4. Habito, R. C., Montalto, J., Leslie, E., & Ball, M. J. (2000). Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult males. British Journal of Nutrition, 84(4), 557-563.
5. Mitchell, J. H., Cawood, E., Kinniburgh, D., Provan, A., Collins, A. R., & Irvine, D. S. (2001). Effect of a phytoestrogen food supplement on reproductive health in normal males. Clinical science, 100(6), 613-618.