In the eighties, scientists discovered the alpha- and beta-receptors for estrogens. Estrogens, like all hormones, act by using receptors located on the cell, which provokes some reaction. The alpha-receptors are linked with a risk of estrogen related cancers. On the other hand, the beta-receptors initiate only favourable effects. The repartition of these two types of receptors in the cells and organs is different. Different tissues appear to have different ratios of each receptor type. This discovery allowed us to understand why isoflavones can act differently than estrogens even though the structure of isoflavones is similar to estrogens.
The isoflavones mechanism
How can we explain that isoflavones have an estrogenic effect and an anti-estrogenic effect? When the natural levels of estrogens are low, isoflavones can help the estrogens by activating the beta-receptors. When the natural levels of estrogen are high, for example during Adolescence, the isoflavones bind with the alpha-receptors and prevent the natural estrogens from binding with these receptors. Isoflavones activate the beta-receptor and reinforce the favourable estrogenic properties. On the other hand, isoflavones protect the estrogen alpha-receptors. Consequently the proneness to estrogen-related cancers is lower.
The alpha-receptor can be mainly found in the breast tissue, the uterus, the ovaries, the testicles and the liver. In those places, isoflavones protect the receptor against estrogens and help reduce the proneness to tumors.
The beta-receptors, which exercise favourable effects for health, can be found mainly in the blood cells, the lungs, the prostate, the bladder, bones and thymus. Isoflavones stimulate their function even after the level of estrogens has decreased.
Regulation of the hormonal balance during menopause
Isoflavones regulate the estrogen levels in the body. Isoflavones play a role when the estrogen level is low. The typical symptoms of the menopause, such as hotflushes and night sweat become less severe. When taking daily 40-50mg of isoflavones, the symptoms of menopause will decrease after 2 to 3 weeks. This treatment will also reduce the risk of hormones related tumors, osteoporosis and arterio-sclerosis.
Other isoflavones actions
Most interest in isoflavones has been generated by their potential hormonal effects. But isoflavones have other physiological effects. There are indications that isoflavones can stop the growth of cancer cells through inhibition of DNA replication and reduction in the activity of various enzymes. Isoflavones also have antioxidant effects and inhibit the actions of various growth factors.
More literature about the action of isoflavones
Dietary isoflavones: biological effects and relevance to human health. J Nutr. 1999 Mar;129(3):758S-767S
Biological effects of a diet of soy protein rich in isoflavones on the menstrual cycle of premenopausal women. Am J Clin Nutr. 1994 Sep;60(3):333-40
Phytoestrogens: the biochemistry, physiology, and implications for human health of soy isoflavones. American Journal of Clinical Nutrition, Vol 68, 1333S-1346S