Effects of diet supplementation with wheat bran on serum estrogen levels in the follicular and luteal phases of the menstrual cycle.

There is both epidemiologic and experimental support for the hypothesis that a high-fiber diet can reduce breast cancer risk; this may be due, at least in part, to a reduction in circulating estrogens. This study examined the effects of three levels of wheat bran supplementation (5, 10, and 20 g/d for 2 mo) on the major serum estrogens during both the luteal and follicular phases of the menstrual cycle. The 10- and 20-g supplements, which increased the total dietary fiber intakes to approximately 20 and 32 g/d, respectively, resulted in significant decreases in the luteal serum estrone (P < 0.05 and < 0.02, respectively). The serum estradiol was significantly reduced in the 10-g wheat bran group after 2 mo (P < 0.05); the 20-g supplemented group showed a significant decrease in estradiol at 1 mo (P < 0.02), but not at 2 mo. No changes occurred in the estrone sulfate concentrations. During the follicular phase, the 10-g wheat bran group exhibited a significant reduction in the serum estrone (P < 0.02). Only the serum estrone sulfate showed any reduction with the 20-g supplement, and this just failed to achieve significance (P = 0.07). Serum sex hormone-binding globulin levels were unaffected by wheat bran. When of long duration, these effects may be sufficient to favorably influence breast cancer risk in Western women.