Phytoestrogens are a special group of phytonutrients that occur naturally in most plant foods. The two major classes are isoflavones in soy, and lignans in seeds, whole grains, legumes, fruits, and vegetables.
They’re called phytoestrogens because they interact with estrogen receptors but they’re not estrogen. In fact, they bind so weakly to estrogen receptors that they effectively block estradiol and are therefore better classified as anti-estrogen.
It’s long been observed that phytoestrogen crops such as red clover suppress the estrogen and fertility of livestock. It’s even been proposed that plants evolved phytoestrogens to reduce the fertility of female herbivores and prevent overgrazing.
In a chapter called “Agriculture and Selection for High Levels of Estrogen,” evolutionary biologist Grazyna Jasienska makes the case that ancient humans evolved higher levels of estradiol as a way to adapt to agriculture and phytoestrogen-rich plant food. In that context, it could be said that those of us with agrarian ancestors are “hormonally calibrated” to a relatively high intake of phytoestrogens to shelter us from our own high estrogen.
So, what does this mean for period health? Well, for one thing, it’s fine to eat phytoestrogens like legumes and seeds. They’ve long been part of our traditional diet, and our hormonal system is adapted to them.
How phytoestrogens affect women’s hormones
For women of reproductive age, phytoestrogens have a beneficial anti-estrogen effect and help to promote the healthy metabolism or detoxification of estrogen. Food-based phytoestrogens may even help to prevent some hormone-sensitive cancers.
Heavy periods. By reducing estrogen, phytoestrogens generally make periods lighter. However, if the dose is high enough to suppress ovulation and progesterone (the hormone that lightens periods), the result can be a heavier period.
Endometriosis. In general, phytoestrogens should be neutral for endometriosis, or even slightly beneficial. Some women with endometriosis report a worsening of symptoms with soy which is probably due to soy-induced iodine deficiency or an immune reaction. Read Immune treatment for endometriosis.
PCOS. Phytoestrogens can improve insulin resistance and have been found to have a beneficial effect on the hormonal condition polycystic ovary syndrome.
Hypothalamic amenorrhea. Phytoestrogens cannot correct the estrogen deficiency of hypothalamic amenorrhea. The treatment for hypothalamic amenorrhea is to promote ovulation by eating more. Read my blog post about estrogen deficiency.
Menopause. During menopause, when estrogen is low, phytoestrogens can have a mild pro-estrogen effect. That has led to a great deal of research into the use of phytoestrogen supplements such as soy as an alternative to menopausal hormone therapy. From hundreds of studies and a few meta-analyses, it appears that isoflavones may help hot flushes, but don’t do much, if anything, for other symptoms of menopause.
Thyroid disease. Concentrated extracts of soy isoflavones may suppress thyroid function. Food-based soy is probably okay as long as you also have enough iodine.
In conclusion, phytoestrogens generally have a beneficial anti-estrogen effect in women. They have a mild pro-estrogen effect in menopausal women, which may be beneficial, and a pro-estrogen effect in men and children, which may be detrimental at a high dose.
Ask me in the comments.