What are Soy Isoflavones?

Soy isoflavones.

Soy extracts contain a number of soy isoflavones (SI), including genistein, diadzein, and glycetin, which are structurally similar to estrogen  and exhibit estrogen-like effects, including binding directly to estrogen receptors, inhibiting aromatase, and disrupting estrogen signaling . In general, it is assumed that phytoestrogens act as defense chemicals against insect herbivory, disrupting endocrine function and modifying the insect’s life course and fertility. There are also many examples of similar effects in vertebrate and mammalian herbivores .

SI exert a number of effects relevant to general health, including modulation of enzymatic function, antioxidant activity, immune function, and the mechanisms underlying carcinogenesis . These factors may underlie putative neuroprotective effects and tentative epidemiological observations of a relationship between SI consumption and breast cancer . In terms of effects on brain function, it is theorized that isoflavones are potentially cognitive enhancing. In animal models, some improvements have been observed following SI in the memory function of ovariectomized rodents  and in middle-aged or older rats as a consequence of supplementation with both genistein  and SI , with concomitant improvements in cholinergic  and prefrontal dopaminergic function . In humans, supplementation with SI in females has been shown to significantly improve the physical, but not psychological, symptoms of premenstrual syndrome compared with placebo and, in post-menopausal women, SI has been shown to improve ratings of quality of life , decrease follicle-stimulating hormone and luteinizing hormone, increase estradiol , and have modest positive effects on neurocognitive function and mood ). However, it is notable that only 4 of 7 studies published between 2000 and 2007 reported a positive impact of isoflavones on cognitive function in this group. In hormonally intact humans, a diet rich in SI, as opposed to a depleted diet, for 10 wk improved short- and long-term memory tasks in males and females, with additional improvements in 2 executive function tasks for the females in the cohort. Most recently, SI supplementation for 6 weeks in males was associated with selective improvement in a spatial working memory task in which females usually outperform males .

What are Soy Isoflavones?