Isoflavones metabolism

The importance of the gut microflora in the metabolism of isoflavones has been demonstrated. Antibiotic administration blocks isoflavone metabolism and germfree animals do not excrete metabolites. Moreover, only germfree rats colonized with microflora from a good equol producer excrete equol when fed soy. ... 

According to Rowland et al [92] dietary fat decreases the capacity of gut microbioflora to synthesize equol. Additionally, the subjects may be poor or good equol excretors, confirming that extensive interindividual variation in isoflavone metabolism exists. 

Frankenfeld CL, McTiernan A, Thomas WK, LaCroix K, McVarish L, Holt YL, Schwartz SM, Lampe JW. 2006. Postmenopausal bone mineral density in relation to soy isoflavone-metabolizing phenotypes. Maturitas 53 315-324. 

Burmeister, G. and Hosel, W. (1981) Immunohistological localization of fj-glucosidases in lignin and isoflavone metabolism in Cicer arietinum (L.) seedlings. Planta, 152, 578-86. 

Fig. (3). Chemical structures of major isoflavones, metabolic derivatives, coumestrol and estradiol.

Regarding the formation of these isoflavone derivatives, it is extremely interesting that some people are unable to produce equol or that they produce it in very low amounts. In fact, studies report that a third part of the general population cannot form equol. This demonstrates that the breakdown of isoflavones by the microflora in the gut determines the recovery of the compounds, and that the excretion to the urine of equol and other isoflavones derivatives, such as O-DMA, is dependent on the different composition of intestinal microflora. To confuse the issue even more, some researchers report that the production of isoflavone derivatives, such as equol, also depends on diet and gender a high fat/meat content diet increases equol production in women but not in men, which is explained by promotion of the growth or the activity of the bacterial populations responsible for equol production. On the other hand, no age-related differences for isoflavone metabolism have been reported [12, 13],... 

A different behaviour has been described in non-monogastric animals. Thus, in ruminants, isoflavones are mainly absorbed in the rumen, where the gastrointestinal epithelium is the major site of metabolism and the liver contributing very little to total isoflavones metabolism in these animals [26],... 

First, the deconposition by isoflavone metabolism enzymes could change isoflavones such as daidzein (6) to their metabolites such as equol (7). 

ISOFLAVONES ALSO COULD BE PRODUCED IN HUMAN Body Equol (49) of Isoflavone Metabolism Product with Estrogen Activity... 

Tian L, Dixon RA (2006) Engineering isoflavone metabolism with an artiflcial bifunctional enzyme. Planta 224 496-507... 

Red Clover Derived Isoflavones Metabolism and Physiological Effects in Cattle and Sheep and their Concentrations in Milk Produced for Human Consumption... 

Hedlund, T.E., Maroni, P.D., Ferucci, P.G., Dayton, R., Barnes, S., Jones, K., Moore, R., Ogdert, L.G., Wahala, K., Sackett, H.M., and Gray, K.J. 2005. Long-Term Dietary Habits Affect Soy Isoflavone Metabolism and Accumulation in Prostatic Fluid in Caucasian Men. J. Nutr. 135, 1400-1406. 

An overall osteoprotective effect is associated with soy diets, the major active component being the isoflavones although the contribution (if any) of soy protein has to be clarified. The spine, rather than the femur, appears to be the most consistently protected bone site. The average daily intake in Japanese women is around 50 mg/day and appears to be sufficient to have a long-term protective effect on the spine. In non-Asian, postmenopausal women, the demonstrated effective dose is 80-90 mg/day. In future clinical studies, investigating the effect of isoflavones on bone metabolism, larger scale, randomized, controlled, intervention trials for longer time periods (1-3 years) will be necessary with a standardized source of soy protein/isoflavones and... 

KELLY G E, lOANNOU G E, REEDER A Y, NELSON 0 and WARING M A (1995) The Variable metabolic response to dietary isoflavones in humans. Proc Soc Exp Biol Med 208, 40-43. 

ROWLAND I R, WISEMAN H, SANDERS T A, ADLERCREUTZ H and BOWEY E A (2000) luteriudividual variation in metabolism of soy isoflavones and lignans influence of habitual diet on equol production by the gut microflora. Nutr Cancer 36, 27-32. 

Upid metabolism abnormality in ovariectomized rats by soy isoflavones, daidzin, genistin, and glycitin. Biol Pharm Bull 24, 368-72. 

UESUGi T, FUKUi Y and YAMORi Y (2002) Beneficial effects of soybean isoflavone snpplementation on bone metabolism and serum lipids in postmenopausal Japanese women a four-week study. JAm Coll Nutr 21, 97-102. 

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). 

ANDLAUER w, KOLB J, FURST p (2000) Isoflavones from tofii are absorbed and metabolized in the isolated rat small intestine. JNutr. 130 3021-7. 

HUR H G, LAY J o Jr, BEGER R D, FREEMAN J p and RAFii F (2000) Isolation of human intestinal bacteria metabolizing the natural isoflavone glycosides daidzin and genistin. Arch Microbiol. 174 (6) 422-8. 

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. 

The basic structures of flavanones, flavones, and isoflavones together with coumestrol, an intermediate in the phenylpropane metabolism, are given in Fig. 2. The 3,5,7,3 -tetrahydroxy-4 -methoxyflavanone is a nod gene inducer in Rhizo-bium leguminosarum bv. viciae the 3, 4, 5,7-tetrahydroxyflavone, in Rhizobium ineliloti and 4,7-dihydroxyisoflavone, in Bradyrhizobium japonicum. Coumestrol, an intermediate in phenylpropane metabolism, is only a weak inducer (7). 

Several studies have evaluated dietary supplements such as isoflavones, which are found in soy products and red clover. A well-controlled trial in more than 400 postmenopausal women evaluating a specific isoflavone, ipriflavone, found no benefits on bone mineral density or fracture rates after 3 years.47 Nevertheless, because these therapies are available without prescription and are not regulated by the FDA, patients may choose to self-medicate with isoflavones. Lymphocytopenia appeared in several patients treated with ipriflavone in clinical trials. Additionally, ipriflavone should be used with caution in immunocompromised patients or those with renal disease. It may inhibit CYP1A2 and CYP2C9 and may interact with drugs metabolized by those pathways, such as warfarin. 

Cassidy A, Handley B and Lamuela-Raventos RM. 2000. Isoflavones, lignans and stilbenes — origins, metabolism and potential importance to human health. J Sci Food Agric 80(7) 1044-1062. 

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