Metabolism of phytoestrogens

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. 

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. 

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

Kaldas R.S., Hughes G.L. (1989) Reproductive and general metabolic effects of phytoestrogens in mammals. Reprod. Toxicol. 3, 81—9. 

Nikolic D, Li Y, Chadwick LR, Grubjesic S, Schwab P, Metz P, et al. Metabolism of 8-prenylnaringenin, a potent phytoestrogen from hops (Humulus lupulus), by human liver microsomes. Drug Metab Dispos 2004 32 272-279. 

Patel RP, Bames S (2010) Isoflavones and PPAR signaling a critical target in cardiovascular, metastatic, and metabolic disease. PPAR Res. doi 10.1155/2010/153252 Patisaul HB, Jefferson W (2010) The pros and cons of phytoestrogens. Front Neuroendocrinol 31 400-419... 

Joannou, G.E., Kelly, G.E., Reeder, A.Y., Waring, M., and Nelson, C., A urinary profile study of dietary phytoestrogens The identification and mode of metabolism of new isoflavo-noids, J. Steroid Biochem. Mol. Biol., 54, 167-184, 1995. 

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

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. 

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