The European Food Safety Authority (EFSA) has conducted a comprehensive review of the available scientific evidence and released a report that says there is “no indication that isoflavones at levels typically found in food supplements cause harm to post-menopausal women.” Isoflavones are naturally occurring substances which are found, among other sources, in soy, red clover, and kudzu root.
Reviewing 43 human studies and 62 animal studies, the Panel on Food Additives concluded it is safe for post-menopausal women to consume soy isoflavones daily without concern of breast and uterine cancer and thyroid function. Specifically the panel concluded that:
Interventional human trials and population studies did not suggest an association between exposure to isoflavone and adverse effects in mammary glands in post-menopausal women.
No reported statistical changes in endometrial thickness and no cases of endometrial carcinoma/uterine cancer in post-menopausal women taking up to 150 mg of isoflavone supplement for up to 2.5 years compared to controls.
In controlled, randomized studies, there was no clinically relevant effect on thyroid function detected in post-menopausal women with normal thyroid function.
Although the isoflavone doses in the reviewed human intervention studies ranged from 30–900 mg/day, the panel did not set recommended values; they indicated a typical supplement can range from 35–150 mg/day of isoflavones. The panel also suggested people can get isoflavones by eating soy-based foods and beverages. For example, firm tofu has about 29 mg of isoflavones per half-cup serving, soy milk has 27 mg per 1-cup serving, and 1 oz of soy protein isolate has 27 mg, according to the U.S. Dept. of Agriculture (USDA) database.
