The female hormones estrogens influence not only reproductive function, but also learning and memory. In postmenopausal women, a lack of estrogen increases the incidence of Alzheimer’s disease (Mayo Clin. Proc. 75 (2000), pp. 1174–1184.). Soy has a high estrogenic potency, and if soy intake is high, this kind of diet may trigger many of the biological responses. In the brain, soy-enriched diet increased the size of sexually dimorphic nucleus of the hypothalamus of males while decreasing it in females while other hypothalamic nuclei (e.g., anteroventral periventricular) displayed opposite reaction to the soy diet (Neurotoxicology and Teratology Volume 24, Issue 1, January-February 2002, Pages 5-16).

The results published in October 2010 issue of the Phytotherapy Research journal (pages 1451–1456) showed that soy isoflavones can improve memory in the intoxicated (chronically aluminum exposed) mice, possibly by modulating the metabolism of brain neurotransmitters. However, a recent study suggested that soy phytoestrogens may improve working memory through estrogen-independent mechanisms (Nutritional Neuroscience, Volume 11, Number 6, December 2008 , pp. 251-262(12).

“Possible beneficial effects (e.g., reduction of serum lipids, increased bone mineral density, relief of hot flashes and other menopausal symptoms, mammary and prostate cancer chemoprevention) in humans have been attributed to consumption of isoflavones but evidence for potential adverse effects (e.g., stimulation of estrogen-dependent mammary tumors and aberrant perinatal development) has also been reported in experimental animal models.” — Daniel R. Doerge (Toxicology and Applied Pharmacology, Article in Press)