Does Too Much Fiber Lower Testosterone?

The brain releases luteinizing hormone, which is then sent to the testes where it stimulates testosterone production. Testosterone plays a role in numerous functions, from building muscle to increasing libido. If you plan on maximizing your testosterone levels, adhering to a high-fiber diet may be doing more damage than good.

Dietary Fiber

Although dietary fiber is indigestible, it plays a role in lowering cholesterol, balancing intestinal pH, regulating blood sugar and providing satiety. In addition, it increases stool bulk and normalizes bowel movements. According to the Mayo Clinic, adults should aim for 25 to 35 grams of fiber per day. Good sources of fiber include whole grains, nuts, beans, vegetables and apples.

Low-Fat, High-Fiber Diet

High-fiber diets may lower testosterone levels, according to a study conducted by researchers at Helsinki University Central Hospital in Finland. Scientists found that healthy middle-aged men changing from their regular diet to a low-fat, high-fiber diet experienced significant decreases in testosterone levels, according to research reported in the March 1983 issue of "Journal of Steroid Biochemistry. 2

Additional Research

Results similar to the previously mentioned study were also reported in the June 2005 issue of the "Journal of Clinical Endocrinology and Metabolism.” Researchers at the Harbor University of California at Los Angeles Medical Center and Los Angeles Biomedical Research Institute investigated the effects of a low-fat, high-fiber diet on healthy men 3. Subjects followed a high-fat, low-fiber diet and then switched to a low-fat, high-fiber diet for eight weeks. Testosterone levels were measured before and after the study. Scientists observed that subjects experienced a small but significant decrease in testosterone levels while following a low-fat, high-fiber diet.

Cruciferous Vegetables

Although high-fiber diets may decrease testosterone, you should still aim to consume 25 grams of dietary fiber a day. Cruciferous vegetables, such as broccoli, cabbage and cauliflower, contain fiber and may indirectly improve testosterone levels. They contain compounds called indole-3-carbinol, which increase urinary excretion of estrogen. Lower levels of estrogen equal higher levels of testosterone. Researchers at Rockefeller University discovered that men and women consuming indole-3-carbinol for three months experienced increases in urinary excretion of estrogen. The findings were published in the March 1997 issue of "Journal of the National Cancer Institute.”