A Primal Primer: Estrogen

The human endocrine system exists in a state of delicate balance. None of its constituents function in a vacuum, and trying to explain every hormonal interrelationship would take volumes, but one statement is fairly safe to make: one hormone affects another. Secreting one often inhibits the next, which in turn sets off an entirely different chain reaction of hormonal secretions, inhibitions, and syntheses. I almost feel like trying to micromanage your entire endocrine system is tedious and counterproductive (and probably impossible to do effectively). I much prefer to simply eat right, exercise smart, get good sleep, normalize stress, and take advantage of simple lifestyle hacks. Still, it doesn’t hurt to understand some of the major hormonal players, especially one as widely maligned by the strength and fitness community as estrogen.

When people talk about estrogen, people are usually referring to estradiol, which is the major form of estrogen in both men and post-pubescent, pre-menopausal women (after menopause, estrone is the major estrogen, while estriol appears mostly during pregnancy). Today, for our purposes, estrogen will refer to estradiol, since it’s the hormone with the most wide-ranging effects on both men and women:

Skeletal Growth

Estrogen inhibits increases in height, with estrogen therapy having been used to effectively “normalize” the heights of tall girls. It’s also an important player in bone mineralization for both sexes, but especially for women; people with genetic aromatase (the enzyme responsible for synthesizing estradiol from testosterone) deficiency often suffer from unchecked vertical growth and poor bone density because they are unable to produce normal amounts of estrogen. Estrogen replacement therapy generally rectifies this.

Female Reproduction

Estrogen is responsible for the maturation of the female sex organs: thickening of the vaginal wall, production of natural lubrication, growth of the cervical glands, growth of the various walls of the uterus. It helps prepare the uterus for implantation, and baboon research indicates that estrogen production is crucial for sustaining a pregnancy and avoiding a miscarriage.

Male Reproduction

Though testosterone is responsible for most male reproductive development, estrogen inhibits sperm cell apoptosis, or cell death, in vitro (try having kids with a bunch of suicidal sperm at your disposal), and the testes are rife with estrogen receptors. Most research confirms that estrogen indeed plays an important role in male gonadal function. Interestingly and somewhat paradoxically, excessive estrogen levels have been linked to low sperm counts, but it’s obviously not a simple “more estrogen/bad for sperm, less estrogen/good for sperm” type of thing.


Women suffering from clinical depression produce far less estrogen (and more testosterone) than normal, and estrogen replacement therapy tends to alleviate their condition. Depressed men produce far more estrogen than normal.

Arterial Function

In women, estrogen appears to increase the function of atherosclerotic coronary arteries. Estradiol production remains high in women until menopause, perhaps explaining the relative paucity of heart events in pre-menopausal women.

Brain Health

In animal Alzheimer’s disease models, estrogen was shown to reduce the formation of amyloid plaques in the brain. In vitro, estradiol displayed potent neuronal protection against oxidative stress, while other steroid hormones did not.


Most breast cancers (as many as 80% of cases) contain estrogen receptor sites and rely on estrogen for “fuel.” A common, effective treatment for these types of breast cancers is suppression of estrogen production and function. Males exposed to supranatural levels of estrogen in the womb are at a greater risk for developing both testicular cancer and prostate cancer as adults.

Estrogen seems pretty useful, right – so why the bad rap? Estrogen gets a bad rap from a lot of (male, bodybuilding) people because it’s responsible for the secondary sexual characteristics of females: fat deposition in the breasts, hips, and butt, along with a widening of the hips (man, what grave injustices evil estrogen perpetrates on women – curves, breasts, and the hourglass shape). Excess estrogen in men can even lead to gynecomastia. Men, by and large, don’t desire these characteristics on their own bodies (others’ bodies is an entirely different story). Estrogen also has the reputation of reducing strength and lean muscle mass while promoting body fat accumulation, as estrogen-dominant males are often obese and under-muscled – check out this article from a bodybuilder’s perspective for exhaustive info on how estrogen can actually promote fat burning and appetite suppression. It’s definitely coming from a different perspective, but it’s useful for breaking down some estrogen myths. And finally, the idea of “height stunting” sounds negative when you first hear it, but then you realize that unchecked growth can have terrible health consequences.

Read that back – “estrogen-dominant.” It’s not the mere existence of estrogen that poses a problem. It’s the preponderance of large amounts of estrogen throwing off the delicate hormonal balance and causing problems. To assign blanket blame to estrogen misses the mark. We (both males and females) produce estrogen for a reason – it has some pretty important responsibilities in the human body. We need the stuff. The real issue lies in unnatural amounts of the hormone and unnatural resistance to the hormone. Insulin isn’t the problem; it’s insulin resistance brought on by Neolithic foods causing chronic, unnatural increases in insulin that we need to worry about. Estrogen isn’t the problem; it’s estrogen dominance brought on by exogenous phytoestrogens (from food, like soy, bran, and other legumes) and xenoestrogens (from plastics, pesticides, herbicides, and other synthetics). I’ve discussed the potential complications arising from widespread exposure to bisphenol A, a potent xenoestrogen, in the past, but we live amidst dozens of various other estrogen-like compounds – and it’s not a stretch to think they might be disrupting our natural hormonal balance.

Estrogen is absolutely necessary, for both men and women. Estrogen imbalance in males and post-menopausal women can lead to fat gain and muscle loss, but it’s unwise to demonize a hormone for transgressions committed in a false, unnatural state.

Stay tuned next week for more on exogenous sources of estrogen. Thanks for reading and Grok on!

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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