Phytoestrogens metabolism

Numerous questions concerning the effects of phytoestrogen supplements for women remain unanswered. Further studies should be performed to clarify the effects of isoflavone extracts, their optimal doses, the significance of individual variation in phytoestrogen metabolism and long-term effects, particularly on men. Risk, benefits, and interactions between phytoestrogens and drugs also need to be carefully evaluated. 

Teas, J., Hurley, T., Hebert, J., Franke, A., Sepkovic, D., and Kurzer, M. (2009). Dietary seaweed modifies estrogen and phytoestrogen metabolism in healthy postmenopausal women. /. Nutr. 139,939. 

Phytoestrogens may also modulate the concentration of endogenous steroid hormones by binding to and inactivating the enzymes involved in their biosynthesis and metabolism. 

MEi J, YEUNG s s, RUNG A w (2001) High dietary phytoestrogen intake is associated with higher bone mineral density in postmenopausal but not premenopausal women, J Clin Endocrinol Metabol 86(11), 5217-21. 

The mucosa of the GIT represents an interface between the external and internal environments. The expansive surface area is necessary for the efficient hydrolysis of foodstuffs and the absorption of energy and nutrients. The mucosa also influences the systemic availability of non-nutrient compounds in the diet, both beneficial and detrimental. Digestion and absorption of glucosinolates are critical determinants of health benefits (see Chapter 4) Similarly, the bioavailability and health benefits of phytoestrogens, such as genistein (see Chapters 5 and 10) are at least partly dependent on the carrier-mediated processes of absorption associated with the GIT (Oitate et al, 2001). Moreover, the metabolic activities of the mucosa can influence the systemic concentrations and forms of dietary phytochemicals, as exemplified by research with soy isoflavones (Andlauer et al., 2000). 

ROWLAND I, WISEMAN H, SANDERS T, ADLERCREUTZ H and BOWEY E (1999) Metabolism of oestrogens and phytoestrogens role of the gut microflora. Biochem Soc Trans. 27 (2) 304-8. 

SETCHELL K D, ZIMMER-NECHEMIAS L, CAI J and HEUBI J E (1998) Isoflavone Content of infant formulas and the metabolic fate of these phytoestrogens in early life. Am. 1 Clin Nutr. 68 (6 Suppl) 1453S-1461S. 

Three dietary intervention studies reported the effects of soy or soy phytoestrogen consumption on reproductive hormones in men and very modest alterations of doubtful clinical significance were found (Habito et al., 2000 Nagata et al., 2001). None of these studies evaluated the prostate itself, and it is possible that soy consumption alters local hormone metabolism and action within the gland. 

Milligan, S.R. et al.. Identification of a potent phytoestrogen in hops (Humulus lupulus L.) and beer, J. Clin. Endocrinol. Metabol, 84, 2249, 1999. 

The basis for understanding the health benefits of isoflavones requires detailed knowledge on the absorption, distribution, metabolism, elimination, and bioavailability of these phytoestrogens that demands robust, precise, accurate, and affordable analyses from biological and other matrices. 

King R. 2002. Digestion, absorption, and metabolism of isoflavones. In Gilani G, Ed. Phytoestrogens and Health. Illinois AOCS Press, PP. 209-234. 

Unlike the phytoestrogens mentioned earlier, flavones do not possess estrogenic activity. However, the flavones apigenin and luteolin act as potent inhibitors of aromatase and 17P-hydroxy-steroid oxidoreductase, enzymes involved in estrogen metabolism. Studies have also demonstrated these flavones and several glycosylflavones are potent goitrogens, particularly in association with millet consumption. 

Certain phytoestrogens have also been suggested to inhibit enzymes involved in estrogen biosynthesis and metabolism, as well as thyroid biosynthesis. Preliminary studies suggest they inhibit protein kinases and topoisomerases, as well as influence the cell cycle and subsequent proliferation, differentiation and apoptotic pathways. Interest in phytoestrogens, such as isoflavones, has increased since they are reported to exhibit some nonhormonal effects, such as antioxidation. 

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