Phytoestrogens and Health Effects

Abstract

Phytoestrogens are literally estrogenic substances of plant origin. Although these substances are useful for plants in many aspects, their estrogenic properties are essentially relevant to their predators. As such, phytoestrogens can be considered to be substances potentially dedicated to plant-predator interaction. Therefore, it is not surprising to note that the word phytoestrogen comes from the early discovery of estrogenic effects in grazing animals and humans. Here, several compounds whose activities have been discovered at nutritional concentrations in animals and humans are examined. The substances analyzed belong to several chemical families, i.e., the flavanones, the coumestans, the resorcylic acid lactones, the isoflavones, and the enterolignans. Following their definition and the evocation of their role in plants, their metabolic transformations and bioavailabilities are discussed. A point is then made regarding their health effects, which can either be beneficial or adverse depending on the subject studied, the sex, the age, and the physiological status. Toxicological information is given based on official data. The effects are first presented in humans. Animal models are evoked when no data are available in humans. The effects are presented with a constant reference to doses and plausible exposure.

Keywords: bone health; cancer; cardiovascular; health; hypothyroidism; menopause; metabolism; nutrition; phytoestrogens; reproduction; toxicology.

Figure 1

Chemical structures of the main phytoestrogens and their precursors beside the molecular structure of estradiol.

Figure 2

Cellular pathways triggered by estradiol via the nuclear ER, Membrane ER, and membrane GPER.

Figure 3

In vitro relative potencies of phytoestrogens. The scale does not take into account the metabolism and the bioavailability of the compounds. 8-PN: 8-prenylnaringenin; Coum: coumestrol; ZEN: zearalenone and zearalenol; Isofl-OH: hydroxylated isoflavones (C4′ position), i.e., genistein, daidzein, equol and glycitein; ENL: enterolignans, i.e., enterodiol and enterolactone; Isofl-CH3: methoxylated isoflavones (C4′ position), i.e., biochanin A and formononetin.

Figure 4

Global features of isoflavone metabolism in animals and human beings.

Figure 5

Metabolic transformation of lignans into estrogenic enterolignans by gut bacteria clusters.