High serum levels of
testosterone and
estradiol, the bioavailability of which may be increased by Western dietary habits, seem to be important risk factors for postmenopausal
breast cancer. We hypothesized that an ad libitum diet low in animal fat and refined
carbohydrates and rich in low-glycemic-index foods, monounsaturated and n-3
polyunsaturated fatty acids, and
phytoestrogens, might favorably modify the hormonal profile of postmenopausal women. One hundred and four postmenopausal women selected from 312 healthy volunteers on the basis of high serum
testosterone levels were randomized to dietary intervention or control. The intervention included intensive dietary counseling and specially prepared group meals twice a week over 4.5 months. Changes in serum levels of
testosterone,
estradiol, and
sex hormone-binding globulin were the main outcome measures. In the intervention group,
sex hormone-binding globulin increased significantly (from 36.0 to 45.1 nmol/liter) compared with the control group (25 versus 4%,; P < 0.0001) and serum
testosterone decreased (from 0.41 to 0.33 ng/ml; -20 versus -7% in control group; P = 0.0038). Serum
estradiol also decreased, but the change was not significant. The dietary intervention group also significantly decreased
body weight (4.06 kg versus 0.54 kg in the control group), waist:hip ratio, total
cholesterol, fasting
glucose level, and area under
insulin curve after oral
glucose tolerance test. A radical modification in diet designed to reduce
insulin resistance and also involving increased
phytoestrogen intake decreases the bioavailability of serum
sex hormones in hyperandrogenic postmenopausal women. Additional studies are needed to determine whether such effects can reduce the risk of developing
breast cancer.