Soy products contain isoflavones, compounds that have estrogen-like properties. In men, higher levels of estrogen equal lower levels of testosterone. As a result, men may worry that consuming soy will increase estrogen and decrease testosterone. There are conflicting results regarding soy's ability to reduce testosterone levels in the body.
Testosterone
Testosterone is an androgen found in both men and women, but predominantly in males. This hormone is responsible for a number of functions in your body, including muscular development, libido and bone function. Testosterone naturally starts to decline with age and is often the cause of muscle loss and lack of sexual desire. Signs of low testosterone are increased body fat, infertility and tender breasts, according to the Mayo Clinic.
Decreases Testosterone Levels
Soy might reduce your testosterone levels, according to a study conducted by scientists at the University of Medicine and Dentistry of New Jersey/Robert Wood Johnson Medical School. They examined the impact of soy protein powder on testosterone levels in male participants. Subjects consumed two scoops of soy protein powder, which contained 56 g of soy, daily for 28 days. Researchers reported in the April 2007 issue of "Cancer Epidemiology, Biomarkers & Prevention" that subjects experienced decreases in testosterone levels. In addition, testosterone levels increased within two weeks after discontinuing soy protein powder use.
No Changes in Testosterone
Another study published in the December 2006 issue of "European Journal of Clinical Nutrition" contradicts this finding. Scientists from the University of Hawaii studied the effects of a high-soy diet on testosterone levels. Participants were assigned to either a high-soy diet, which contained two daily soy servings; or a low-soy diet for three months. At the end of the study, researchers found that those in the high-soy diet group experienced no change in testosterone levels compared with those in the low-soy diet group.
Considerations
If you are allergic to soy or have kidney disease, you should avoid soy use. In addition, soy consumption might disrupt normal thyroid function; however, further research is necessary, according to the University of Maryland Medical Center. Consult your health care provider before consuming soy.
References
- Mayo Clinic; Testosterone Therapy: Key to Male Vitality?; April 2010
- "Cancer Epidemiology, Biomarkers and Prevention"; Clinical and Biological Activity of Soy Protein Powder Supplementation in Healthy Male Volunteers; S. Goodin et al.; January 2007
- "European Journal of Clinical Nutrition"; Serum Prostate-Specific Antigen But Not Testosterone Levels Decrease In Randomized Soy Intervention Among Men; G. Maskarinec et al.; December 2006
- University of Maryland Medical Center; Soy; 2011
