deep dive into phytoestrogens

Phyto-estrogen refers to a plant-derived substrate that behaves like oestrogen and activates the oestrogen receptor (ER) within humans and other mammals.
They can be found in a wide range of grains, seeds, legumes and medicinal plants. 

Phytoestrogens are known to influence the menstrual cycle, reduce incidence of oestrogen-responsive cancers and decrease severity of menopausal substances (Nagata et al., 2006; Guha et al., 2009; Kurzer, 2008).

The most commonly consumed phytoestrogen are known as flavonoids or isoflavaonoids, which possess a structural similarity to the human oesotrgen molecule, this allows them to bind to ERs.

Isoflavones are found in small amounts in a number of legumes, grains, and vegetables, however soybeans are by far the most concentrated source. High isoflavone intake from soy foods in Asian countries (average range, 25 to 50 mg/day) has been suggested to contribute to reducing the risk of breast cancer; in contrast, the incidence of breast cancer remains elevated in Europe, North America, and Australia/New Zealand where average isoflavone intakes in non-Asian women are generally less than 2 mg/day. Nevertheless, several hereditary and lifestyle factors likely also contribute to this difference.

Soy products that are fermented and aqueous washed are far higher in total isoflavones (including miso, mature seed/ dry roasted soybeans, tempeh) compared to soy-based meat substitutes, soy milk, soy cheese and soy yoghurt or ethanol washed products.

The study of phytoestrogens is complex and ever-evolving, and it should be understood that there are two major types of ERs in the body; ER-alpha (more widely known) and ER-beta (discovered less than 30 years ago).

Oestrogen and ER-α create an interaction that is responsible for the growth of hormone- sensitive tissues (proliferation-enhancing effects) therefore playing a large role in the menstrual cycle and changes during pregnancy. ER-α is also involved in bone turnover such that over-activation is related to osteoporosis. Over-activation of ER-α has also been related to the growth of hormone-sensitive tumors such as breast, endometrial and prostate cancer.

ER-β has complex functions, but in many ways counteract processes induced by ER-α.
ER-β prevents an overstimulation of proliferating tissue, in the breast or uterus for example.
The precise outcome of the mix of activations of these two receptors will depend on the receptor distribution in the organs. Therefore, terming a food or plant as a phytoestrogen lacks sufficient discrimination between compounds that will bind to ER-β or ER-α, and have quite opposing effects. 

The effect might be pro-or anti-oestrogenic depending on the physiological environment, for example:
- When post-menopausal women (who are oestrogen-deprived) consume isoflavones an oestrogen-like effect can be observed through reduction of hot flushes by activation of ER- β receptors.
- When women of child-bearing age (with relative oestrogen levels) consume isoflavones they may experience an anti-oestrogenic effect causing lighter periods or prolongation of the menstrual cycle by one or two days.

Therefore phytoestrogens can have effects that are considered both ‘oestrogenic’
- increase in bone density
- cardiovascular protection
- reduction in menopausal symptoms

While at the same time possessing actions that are considered ‘anti-oestrogenic’
-inhibition of cancer initiation and progression
- neo-angiogenesis.

The composition of one’s colonic microbiota (gut flora) can also influence the biological effects of isoflavones. Some of the potential health benefits of soy intake are thought to depend on one’s capacity to convert isoflavones to key metabolites during digestion. Specifically, some colonic bacteria can convert the soy isoflavone to a metabolite that has greater oestrogenic activity than to other metabolites that are less estrogenic.

The extent to which soy isoflavones exert estrogenic and anti-estrogenic effects in humans is currently the focus of considerable scientific research.

References:

https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/soy-isoflavones

Women, Hormones & the Menstrual Cycle. 1998. R, Trickey.