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 must not 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 in that she needs to do a lot more than just be healthy and make a few hormones. A woman’s hormonal system has to make the life-or-death decision of whether there is likely to be an additional 75,000 calories available to safely complete a pregnancy.
If the hypothalamus perceives signals from the environment that food is scarce (or likely to be scarce), then the hypothalamus will make the very sensible decision to switch off reproduction.
Is carbohydrate availability part of the “signal” to ovulate?
What are the dietary signals that the hypothalamus is waiting for? Well, adequate calorie intake for starters. And almost certainly adequate protein intake. And there is reason to believe that the hypothalamus is also waiting for adequate carbohydrate intake for some women.
There is substantial anecdotal evidence from myself and colleagues that some young women develop amenorrhea (lack of periods) on a low-carb or keto diet, even when there are sufficient calories and protein.
Physiologist Professor Anne Loucks says 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.
1) This doesn’t apply to men, 2) it probably doesn’t apply to women over 30 or women who have insulin resistance, and 3) it depends on ancestry. In other words, starch signalling may be more important for women descended from agrarian ancestors.
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.
But what if you have insulin resistance?
If you currently have insulin resistance, you may do well on a low-carb or keto diet. Especially if you’re older than 30. You may even regain the periods you’d lost to a high-carb diet.
But step one to reversing insulin resistance is to cut sugar, not all carbohydrates. That’s because high-dose fructose induces insulin resistance more strongly than any other food. According to Dr Richard Johnson:
“There’s a fair amount of evidence that starch-based foods don’t cause weight gain like sugar-based foods and don’t cause the metabolic syndrome like sugar-based foods. Potatoes, pasta, rice may be relatively safe compared to table sugar. A fructose index may be a better way to assess the risk of carbohydrates related to obesity.”
Quitting sugar is the most effective kind of low-carb diet, so please don’t make the mistake of forgoing potatoes only to binge on Paleo desserts. Read High-dose fructose can cause or worsen insulin resistance (but fruit is okay).
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, then you may benefit from a short-term low-carb or keto diet but only until you’ve reversed insulin resistance. If no, then a keto diet is probably not the right approach.
- Do you suffer 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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