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By Dr Lara Briden
As more women move to restricted diets such as “clean eating”, vegan, or keto, more women are losing their periods.
Losing periods to undereating is called hypothalamic amenorrhea, and it’s common.
How does under-eating stop periods?
Too few calories or too little of any macronutrient can switch off signalling from the hypothalamus to the ovaries. It’s an ovarian “off switch” and not a malfunction. It’s a woman’s hormonal system working exactly the way it’s supposed to work.
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”?
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 that some young women become amenorrheic (lose periods) on a low-carb or keto diet — even when they are eating sufficient calories and protein.
Also, physiologist Prof 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.
Why does it matter?
Menstrual cycles are not just for making a baby. Ovulation and the making of ovarian hormones are also highly beneficial for general health.
For example, every monthly dose of estrogen promotes muscle gain, insulin sensitivity, and the long-term health of bones, brain, and the cardiovascular system. Every monthly dose of progesterone reduces inflammation, regulates the immune system and supports thyroid, brain, bones, and breast tissue.
According to Canadian endocrinology professor Jerilynn Prior, “women benefit from 35 to 40 years of ovulatory cycles, not just for fertility but also to prevent osteoporosis, stroke, dementia, heart disease, and breast cancer.” In that sense, each and every ovulation is like a monthly deposit into the bank account of long-term health.
What if you have PCOS?
Women with polycystic ovary syndrome (PCOS are often told to avoid carbohydrate. Reducing carbohydrate can definitely be helpful for the insulin-resistant type of PCOS. It’s less helpful for other types of PCOS or for hypothalamic amenorrhea that has been misdiagnosed as PCOS because there were polycystic ovaries on ultrasound. Read Maybe It’s Not PCOS.
Hormonal birth control is not the answer
The pill doesn’t solve the problem of amenorrhea because pill-bleeds are not periods and contraceptive drugs are not hormones. The current consensus is that the pill does not improve bone density, and one study found that the pill can actually impair recovery from hypothalamic amenorrhea.
The solution is to eat more. A lot more. To recover from hypothalamic amenorrhea, most women need at least 2500 calories per day, including some starch. Recovery can take at least six months.
If you’re frightened by the idea of eating more, please consider whether you have an eating disorder and reach out for help. One possible resource is The Eating Disorder Association of New Zealand.
Bio: Lara Briden is a naturopathic doctor and Executive Member of the Society (AHSNZ). She is also the author of the bestselling book Period Repair Manual.