Flax seeds are rich in lignans (fibre) and phytoestrogens. Phytoestrogens are plant substances with estrogen-like properties. In the body, they can prevent negative effects of estrogens made by our bodies. They do this either by blocking estrogen actions or by replacing estrogen at estrogen receptor sites without stimulating the receptor. Lignans in flax seed bind testosterone in the same manner as for estrogen. Researchers at Duke University found that supplementation with milled flax resulted in significant decreases in both total and free testosterone in prostate cancer patients. They also found a decrease in PSA levels in men with early stage prostate cancer. Flaxseed also is rich in alpha-linolenic acid that is both an essential fatty acid and an omega-3 fatty acid. Researchers are interested in omega-3 fatty acids for their roles in reducing risk factors for heart disease and stroke (regulation of cholesterol, triglycerides, blood pressure, blood clotting), immune and inflammatory disorders.
I think they are a reasonable thing to supplement into the diet