Japanese postmenopausal women in Japan have about one ninth the rate of American postmenopausal women. Rates of breast cancer double even after just ten years among Japanese women who migrate to the US. Diet is thought to be an important factor, and the investigators were interested in whether dietary seaweed, with and without soy supplements, could influence known biomarkers of breast cancer risk in American women.

33 healthy postmenopausal women were randomized to 6 wk seaweed then 1 wk seaweed plus soy or 6 wk placebo then 1 wk placebo plus soy. Blood and urine samples were collected at the end of each treatment period and analyzed for estrogen, homocysteine, antioxidants, insulin-like growth factors and thyroid hormones. Urine was analyzed for phytoestrogens and iodine.

Inclusion Criteria:

• Postmenopausal (self-reported cessation of menstruation 1 y prior to enrollment)
• If breast cancer survivor, all therapy completed at least 6 months prior to enrollment
• Agreed to eat their normal diet, avoiding seaweeds and phytoestrogen-rich foods,
• Restricting alcoholic intake to #2 drinks (24 g alcohol)/wk -Continuing habitual intake of vitamins, supplements, and medications during the study. -

Exclusion Criteria:

• No allergies to seaweed, soy, shellfish, or iodine
• No current use of tobacco;
• No thyroid dysfunction or treatment within the previous 5 y;
• Negative thyroid peroxidase antibodies as determined by screening;
• No hormone replacement therapy or for breast cancer survivors, no chemotherapy or radiation treatments within the preceding 6 mo
• No history of cancer (other than breast cancer)
• No current gastrointestinal disorders or diabetes; omnivorous eating habits, including meat and dairy products at least twice/wk
• No oral antibiotics, iodine containing medications, or corticosteroids treatment within the previous 3 mo.