Genistein is a polyphenol that is found in soybeans and other plants, such as red clover and kudzu. It is a type of flavonoid known as an isoflavone. Genistein is frequently found with the isoflavone daidzein, and together they are considered soy isoflavones. These compounds have been widely studied for their effects on human health. They have been associated with a reduction in cancer in population studies that examine diets and rates of diseases.
Both of these molecules are capable of binding to animal and human estrogen receptors. Due to this, they are known as phytoestrogens. Receptors stimulate cellular activity when a specific compound binds to them. Genistein binds to estrogen receptors, and stimulates their activity, but not as effectively as human estrogen. Thus, it can partly block the effects of estrogen. This may account for the protective effect against cancers that have hormones involved in their development, such as prostate and breast cancer.
In Asia, soy consumption is much higher than that in the West, and possibly up to 20 times higher. Soy products — such as flour, milk, tofu, and soybeans themselves — are readily consumed. Studies examining the diets of populations of people and their disease rates have found that Japanese men have significantly lower rates of prostate cancer than American men. Also, Asian women have lower rates of breast cancer than Western women. These differences have been hypothesized to be due to the differences in the amount of soy in the diets.
Genistein has been shown to slow the growth of a variety of cancer cells in laboratory studies. It has several different biochemical properties, besides acting as a phytoestrogen, that might result in these effects on cancer cells. Its anti-cancer activity is significant enough that it is listed in the National Cancer Institute’s Drug Dictionary. The timing of its use in treatment is important, however, since some studies have found genistein to increase the spread of existing breast cancer. Treating patients with a compound that blocks estrogen can ameliorate this effect.
This isoflavone also appears to have effects against the bone loss that occurs once menopause has started, and estrogen levels decrease in women. This can cause osteoporosis and be severely debilitating. Estrogen treatment used to be common in post-menopausal women to prevent these effects, but research has shown it to have dangerous side effects. Treatment with genistein has been found to increase bone density in women who took it as a dietary supplement.
Genistein is also a strong antioxidant. This activity can protect DNA from oxidative damage, and prevent mutations from occurring. It can also keep cholesterol from oxidizing and contributing to the risk of a heart attack. This isoflavone is hypothesized to protect against heart attacks.
There can be side effects from taking this compound as a dietary supplement, however. It can cause gastrointestinal problems. There is some research that suggests it may impair the immune system. Daidzein does not appear to have these side effects. It may be wise to try and get the benefits of soy isoflavones solely by eating more soy, rather than taking genistein dietary supplements.