Phytoestrogens

A number of compounds shown in Figure 14.12 that occur in plant foods as glycosides and other conjugates have weak estrogenic/antiestrogenic actions, and are collectively known as phytoestrogens. They all have two hydroxyl groups that are the same distance apart as the hydroxyl groups of estradiol and can bind to estrogen receptors. The amounts of phytoestrogens produced increase in response to microbial and insect attack, suggesting that they have antibacterial or antifungal actions in the plant. They produce typical estrogen responses in animals, with a biological activity 1/500 to 1/1,000 of that of estradiol.

OH CH3I

I estradiol

I estradiol

Figure 14.12. Estradiol and the major phytoestrogens.

High consumption of legumes, especially soya beans, which are rich sources of phytoestrogens, is associated with lower incidence of breast and uterine cancer, as well as a lower incidence of osteoporosis. The estrogenic action is probably responsible for the effects on the development of osteoporosis, whereas three factors may be involved in the effect on hormone-dependent cancer:

1. The isoflavones are mainly antiestrogenic, because they compete with estradiol for receptor binding, but the phytoestrogen-receptor complex does not undergo normal activation, thus it has only a weak effect on hormone response elements on DNA. Even those phytoestrogens that have a mainly estrogenic action will reduce responsiveness to estradiol because they compete for receptor binding but have lower biological activity.

2. The phytoestrogens increase the synthesis of sex hormone binding globulin in the liver by stabilizing mRNA, leading to a lower circulating concentration of free estradiol.

3. Some of the phytoestrogens inhibit aromatase and therefore reduce the endogenous synthesis of estradiol, especially the unregulated synthesis that occurs in adipose tissue.

FURTHER READING

Bingham SA, Atkinson C, Liggins J, Bluck L, and Coward A (1998) Phyto-oestrogens: where are we now? British Journal of Nutrition 79, 393-406.

Crane FL (2001) Biochemical functions of coenzyme Q10. Journal of the American College of Nutrition 20, 591-8.

Dallner G and Sindelar PJ (2000) Regulation of ubiquinone metabolism. Free Radicals in Biology and Medicine 29, 285-94.

Davies SR, Dalais FS, Simpson ER, and Murkies AL (1999) Phytoestrogens in health and disease. Recent Progress in Hormone Research 54, 185-211.

Johnson I, Williamson G, and Musk SRR (1994) Anticarcinogenic factors in plant foods: a new class of nutrients? Nutrition Research Reviews 7, 175-204.

Kurzer MS and Xu X (1997) Dietary phytoestrogens. Annual Reviews of Nutrition 17, 353-81.

Liao S, Kao YH, and Hiipakka RA (2001) Green tea: biochemical and biological basis for health benefits. Vitamins and Hormones 62, 1-94.

Liu L and Yeh YY (2002) S-alk(en)yl cysteines of garlic inhibit cholesterol synthesis by deactivating HMG-CoA reductase in cultured rat hepatocytes. Journal of Nutrition 132, 1129-34.

Nugon-Baudon L and Rabot S (1994) Glucosinolates and glucosinolate derivatives: implications for protection against chemical carcinogenesis. Nutrition Research Reviews 7, 205-32.

Overvad K, Diamant B, Holm L, Holmer G, Mortensen SA, and Stender S (1999) Coenzyme Q10 in health and disease. European Journal of Nutrition 53, 764-70.

Persky AM and Brazeau GA (2001) Clinical pharmacology of the dietary supplement creatine monohydrate. Pharmacology Reviews Reviews 53, 161-76.

Rebouche CJ and Seim H (1998) Carnitine metabolism and its regulation in microorganisms and mammals. Annual Reviews of Nutrition 18,39-61.

Redmond HP, Stapleton PP, Neary P, and Bouchier-Hayes D (1998) Immunonutrition: the role of taurine. Nutrition 14, 599-604.

Ross JA and Kasum CM (2002) Dietary flavonoids: bioavailability, metabolic effects and safety. Annual Reviews of Nutrition 22, 19-34.

Schaffer S, Takahashi K, and Azuma J (2000) Role of osmoregulation in the actions of taurine. Amino Acids 19, 527-46.

Schwartz B and Klinman JP (2001) Mechanisms of biosynthesis of protein-derived redox cofactors. Vitamins and Hormones 61, 219-39.

Various authors (1996) Colloquium proceedings: bioactive components of food. Biochemical Society Transactions 24,771-835.

Various authors (1996) Symposium proceedings: physiologically active substances in plant foods. Proceedings of the Nutrition Society 55, 371-446.

Vaz FM and Wanders RJ (2002) Carnitine biosynthesis in mammals. Biochemical Journal 361, 417-29.

Wiseman H (1999) The bioavailability of non-nutrient plant factors: dietary flavonoids and phyto-oestrogens. Proceedings of the Nutrition Society 58, 139-46.

Wyss M and Kaddurah-Daouk R (2000) Creatine and creatinine metabolism. Physiolog-icalReviews 80,1107-1213.

Yang CS, Landau JM, Huang MT, and Newmark HL (2001) Inhibition of carcinogenesis by dietary polyphenolic compounds. Annual Reviews of Nutrition 21, 381-406.

Zeisel SH (2000) Choline: an essential nutrient for humans. Nutrition 16, 669-71.

References cited in the text are listed in the Bibliography.

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