Every time I tweet my concern about women losing their periods to a low-carb or keto diet, I get a lot of angry responses.
“It’s purely anecdotal,” men explain to me. “There is no known mechanism, so it can’t really be happening.”
Except it is really happening. Ask anyone who works with young menstruating women. Or not menstruating, as the case may be.
“Does a keto diet stop periods?”
A woman’s hormonal system is different from a man’s because a woman’s hypothalamus is very sensitive to energy deficiency. Not just a little sensitive, like “Oh, I’m a little stressed,” but very sensitive like “Oh, it looks like I’m not likely to have access to the additional 75,000 calories it will take to complete a pregnancy, so I’ll just shut it all down.”
In other words, when the hypothalamus perceives signals from the environment that food is scarce (or likely to be scarce), it will make the entirely logical decision to switch off ovulation. That switches off hormones, so the result is irregular, anovulatory, or no cycles! (And remember pill bleeds are not menstrual cycles.)
Carbohydrate availability is part of the “signal”
The hypothalamus is waiting for dietary signals about food supply. That means adequate calories, adequate protein, and yes, adequate carbohydrates for some women.
There is substantial anecdotal evidence from myself and colleagues that too little carbohydrate can stop periods (especially in young women), even when there are sufficient calories and protein.
Physiologist Professor Anne Loucks observed that, when it comes to maintaining menstrual cycles, the hypothalamus is just as sensitive to carbohydrate availability as it is to total calorie availability. She states that pituitary “LH pulsatility is regulated by brain glucose availability” and “may depend specifically on carbohydrate availability rather than energy availability in women, just as it does in other mammals.”
There are a few things to say at this point.
- Men don’t have the same requirement for carbohydrates because they don’t have to ovulate or hold a pregnancy.
- Women over 35 may not have the same requirement for carbohydrates because their ovulatory cycles are more robust (i.e. less sensitive to being shut down).
- Women with insulin resistance don’t have the same requirement for carbohydrates; in their case, reducing carbohydrates (especially sugar) could actually promote ovulation.
- Finally, it depends on ancestry. Women descended from agrarian ancestors may be more sensitive to carbohydrates as a food signal.
In her book Fragile Wisdom, evolutionary biologist Grazyna Jasienska builds the case that the hypothalamic-pituitary-ovarian (HPO) axis is calibrated to relatively recent ancestry. She calls it “ovarian set point,” which she defines as the ability to ovulate given a particular energy availability.
Like so many things in women’s health, there is almost no research, but one 2003 clinical trial of the keto diet for teenagers found that 45 percent of the female participants lost their periods within six months.
Is a low-carb or keto diet right for you?
Before you start a keto diet, ask yourself:
- Do you have insulin resistance? If yes, you may benefit from a short-term low-carb or keto diet but only until you’ve reversed insulin resistance. If not, then a keto diet is probably not the right approach.
- Do you suffer from stress or insomnia or HPA (hypothalamic-pituitary-adrenal) dysfunction? If yes, then be careful because you might need starch to calm your nervous system.
- Did your period go “missing in action” on a keto diet? If yes, then you might want to try reintroducing starch for a minimum of four months to see if you can get your period back.
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