Abstract
Epidemiological data suggest that regular intake of isoflavones from soy reduces the incidence of estrogen-dependent and aging-associated disorders, such as menopause symptoms in women, osteoporosis, cardiovascular diseases and cancer. Equol, produced from daidzein, is the isoflavone-derived metabolite with the greatest estrogenic and antioxidant activity. Consequently, equol has been endorsed as having many beneficial effects on human health. The conversion of daidzein into equol takes place in the intestine via the action of reductase enzymes belonging to incompletely characterized members of the gut microbiota. While all animal species analyzed so far produce equol, only between one third and one half of human subjects (depending on the community) are able to do so, ostensibly those that harbor equol-producing microbes. Conceivably, these subjects might be the only ones who can fully benefit from soy or isoflavone consumption. This review summarizes current knowledge on the microorganisms involved in, the genetic background to, and the biochemical pathways of, equol biosynthesis. It also outlines the results of recent clinical trials and meta-analyses on the effects of equol on different areas of human health and discusses briefly its presumptive mode of action.
Highlights
Abundant epidemiological evidence suggests that diets rich in phytoestrogen-containing foods, such as soy and soy products, reduce the risk of a number of syndromes and chronic diseases, notably menopause symptoms in women, cardiovascular and neurodegenerative diseases, and certain types of cancer [1,2,3]
Current interest in dietary isoflavones has been driven by epidemiological studies, suggesting that diets rich in phytoestrogens are beneficial to human health
Soy isoflavones and isoflavone-derived metabolites are structurally similar to estrogen and might have some of its effects
Summary
Abundant epidemiological evidence suggests that diets rich in phytoestrogen-containing foods, such as soy and soy products, reduce the risk of a number of syndromes and chronic diseases, notably menopause symptoms in women, cardiovascular and neurodegenerative diseases, and certain types of cancer [1,2,3]. Absorbed aglycones are metabolized mainly lower than in animal models Animal studies may not, be extrapolated to humans They may be further catabolized in the liver or secreted into the bile, returning to the intestine metabolized mainly to glucuronidated and sulphated derivatives by endogenous phase. Certain aglycone conjugates may have estrogenic activity too, and serve as an intracellular reservoir returning to the intestine via the enterohepatic circulation [12]. 456–559 nmol/kg in breast adipose and glandular quantification of the isoflavone derivatives in target tissues has rarely been determined [14]. More absorbed, and has a lower clearance than its precursor molecule daidzein [24] It shows stronger estrogenic activity than any other isoflavone or isoflavone-derived metabolite [23,25]. It is the isoflavone-derived compound with the strongest antioxidant activity [27,28]; antioxidants are thought to have a prominent role in the onset and progress of different chronic diseases, including cancer [29]
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