Phytoestrogens

by Joy Hammond

Phytoestrogens are non-steroidal estrogens that occur naturally in certain plant foods. They are similar to estrogen produced in your body, but are much weaker. However, they have estrogen-like effects only on some tissues and processes in the body, and anti-estrogen effects on other tissues and body processes. Isoflavones are the most noted kind of phytoestrogens in regards to menopause, and are mainly found in soybeans, chickpeas, and other legumes.

Menopause is the time in a woman's life when menstrual periods permanently stop, characterized by a change in levels of hormones with a variable array of symptoms such as hot flashes, night sweats, mood swings, forgetfulness, and trouble sleeping. Other concerns of menopause are osteoporosis, cardiovascular disease, and breast cancer.

Hormone replacement therapy (HRT), the combination therapy of estrogen and progesterone, is currently used to treat menopause symptoms and concerns. It is therefore thought that phytoestrogens might have similar effects.Like other alternative therapies, their popularity precedes their scientific proof of safety and efficacy.

Recent research efforts are directed at understanding what isoflavones do in our bodies when we eat soy.Genistein and daidzein are the two isoflavones with the most estrogen-like activity and under great scrutiny at this time for their therapeutic and medicinal use. Many claims have been made of their effectiveness, such as reducing the symptoms of menopause; having a positive effect on bone mass; lowering blood cholesterol and thereby reducing the risk of heart disease; and preventing certain types of cancer.

Menopausal symptoms are rarely life threatening, however sufferers can be quite miserable.Most women do not choose HRT. Approximately 85% of women in Western cultures have hot flashes and night sweats, but less than 10% of Japanese women have hot flashes and less than 4% have night sweats.This led researchers to focus on the possible effects of soy foods abundant in the Japanese diet. Albertazzi and colleagues studied the effect of isolated soy protein on hot flashes in post-menopausal women.The soy group had a 26% reduction in the mean number of hot flashes by week 3 and a 45% reduction by the end of week 12.This was significantly fewer hot flashes than the milk protein group. Isoflavones do relieve hot flashes but not to the proportion of HRT.

With the decline of estrogen production and presence of estrogen in the body, the destruction of bone is accelerated. Factors other than hormones also influence bone health. Ipriflavone, a medication used in Europe, is noted for osteoporosis prevention. Interestingly, the isoflavone daidzein metabolizes to ipriflavone in the body. Studies on soy phytoestrogens and osteoporosis are limiting because the amount of phytoestrogens in soy is variable and the trials have been short (3-6 months). Like the synthetic ipriflavone, daidzein also inhibits bone resorption, and enhances osteoblast function.

Estrogen has two targets when working against heart disease- the liver and the blood vessels. It dampens liver production of fatty materials, resulting in more high-density lipoproteins (HDL) and less low density lipoprotein (LDL) cholesterols. Estrogen strengthens blood vessels against accumulation of plaque by keeping them resilient. Phytoestrogens have the same effect: decrease LDL and increase HDL cholesterols; help prevent plaque formation and blood clots; and increase arterial elasticity.Most studies show that an intake of 25-50 grams(g) soy protein per day results in about a 10% decrease in serum LDL levels. This doesn't appear to work with isolated isoflavones. These effects are more pronounced in persons with hypercholesterolemia.In the hallmark meta-analysis study conducted in 1995 by Anderson et al., 38 controlled clinical trials found that an average intake of 47g soy protein per day produced an average 13% decrease in LDL cholesterol levels and a 10% decrease in triglyceride levels. Some studies also illustrate that soy isoflavones increase arterial compliance, decrease platelet aggregation, and decrease blood pressure. The Food and Drug Administration (FDA) has concluded from these fifty or more studies that 25g of soy protein in a daily diet low in saturated fat and cholesterol may reduce the risk of heart disease.

Genistein, as the most estrogenic of the phytoestrogens binds more weakly than tamoxifen to the estrogen receptor in breast cells, and reduces endogenous binding to the receptor. It has been shown to inhibit the growth of human breast cancer cells in vitro. A preliminary study by McMichael-Phillips et al. showed 45mg of isoflavones increasing breast cell proliferation, a sign of increased cancer risk. A study published this year by Jenkins et al. concluded that there was no evidence of estrogenic activity in subjects fed 86mg of isoflavones a day. Perhaps the question ought to be concerning the effects of genistein on the breast in the presence of high, moderate and low levels of estrogen throughout the life cycle. Further studies must be done before the true scope of genistein's actions can be understood in regards to breast cancer.

There continues to be a multitude of questions concerning the efficacy and safety of phytoestrogens.Will isoflavones become an acceptable form of HRT in relieving menopausal symptoms such as hot flashes, and useful in inhibiting bone resorption as research illuminates our understanding? The therapeutic and medicinal dose and safety of phytoestrogens still needs to be determined in regards to breast cancer. For now, the FDA approves 25g soy protein per day to reduce the risk of heart disease. That is what is considered true! That is what is safe!