The Weird Way the Ketogenic Diet Affects Your Period
You probably know all about how the keto diet may lead to weight loss and a host of other possible health benefits, but it may also be the reason your cycle is irregular or has halted completely.
The ketogenic, or “keto,” diet — the high-fat, very low carb approach that’s taken the diet world by storm over the past several years — has been linked to weight loss and other health benefits, but it can also have a strange effect on your period. Some women on the keto diet report irregular periods, while others say their monthly cycle vanished altogether — a phenomenon called amenorrhea — after they adopted keto.
In fact, amenorrhea seems to be right up there with weight loss as one of the main side effects of the diet. In some research, 60 percent of study participants reported they lost weight as a result of the diet, and 45 percent of the female participants reported menstrual dysfunction.
The Reason the Keto Diet May Mess With Your Period
What gives? It could be due to the quick weight loss. “If someone is cutting too many calories, cycle irregularities can develop,” says Kristen Kizer, RD, with Pura Vida Behavioural Nutrition in Canberra, Australia.
This can happen with any diet, not just keto, though keto has been shown to lead to drastic weight loss. Previous research found that one year into a low-calorie version of keto, most study participants lost at least 10 percent of their initial body weight. The keto diet can result in quick weight loss because it causes your body to burn fat instead of carbs through a process called ketosis.
John Thoppil, MD, a board-certified obstetrician-gynecologist with River Place Obstetrics and Gynecology in Austin, Texas, says low carb intake has also been linked with disrupted periods, but he says most of that evidence is anecdotal or comes from small studies. He agrees that changes in your period are likely related to weight loss and not keto specifically.
How Does the Keto Diet Affect Hormones?
The irregular or disappearing periods can be traced to hormone changes. “To have a normal period, you have to have a pulsatile release of hormones from the brain,” Dr. Thoppil says. “Any sort of stressor — weight loss or a lot of exercise — can affect that pulsatile release that has to happen for this normal choreography of hormone release that allows you to have regular menses.” A study published in September 2018 in the Journal of Obesity and Weight Loss Therapy noted that keto caused disruption to women’s hormonal systems.
One of the main hormones in play here is estrogen, which is responsible for regulating the menstrual cycle. As weight drops, so do estrogen levels, says Luiza Petre, MD, a board-certified cardiologist and nutrition expert based in New York City. According to previous research, when participants lost an average of 17 pounds, their levels of the estrogen hormone estrone decreased 5.7 percent and the estrogen hormone estradiol dropped nearly 10 percent. The study authors note that weight loss as a result of calorie restriction and exercise significantly decreased estrogen levels.
Another hormone that seems to mess with period regularity is the gonadotropin-releasing hormone (GnRH). GnRH is the signal for pituitary production of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are responsible for stimulating ovarian production of estrogen and progesterone, and therefore ovulation). A small study published in the Journal of Translational Medicine in February 2020 found overweight women with PCOS who followed the keto diet for 12 weeks lost a significant amount of weight and also saw a decrease in the ratio between LH and FSH, which is a healthier balance between the two. Another small study, published in the October 2022 Nutrients involving 25 people with obesity and polycystic ovarian syndrome (PCOS) found the keto diet helped the participants improve their metabolism and ovulatory dysfunction.
Body composition changes (such as those that come with weight loss as a result of the keto diet or another diet) can alter GnRH levels, according to an article published in Endotext in May 2018.
The disruption of GnRH causes reduced estrogen, and these changes can disrupt ovulation and lead to amenorrhea.
How Worried Should You Be if Keto Does Affect Your Cycle?
Decreasing estrogen levels can be a cause for concern. “Lower estrogen levels have certain side effects that go along with that, [such as] vaginal dryness, but the long-term health concern would be the increased risk of bone loss,” Thoppil says. According to the Mayo Clinic, osteoporosis is a known complication of amenorrhea. To protect the bones, he sometimes recommends patients supplement with a natural estrogen. Estradiol (estrace) is an example of a natural estrogen supplement.
Of course, low estrogen and missed periods can also affect fertility. But, “if you’re not worried about getting pregnant, and thus ovulation is not the end all be all, from a pure health standpoint [it’s not much to worry about],” says Thoppil. If you’ve had regular cycles before and continue seeing irregularities for three to six months, he recommends seeing your doctor.
How to Get Your Period Back to Normal on Keto
Thoppil says most people have a threshold, a “happy weight,” where they’ll resume regular periods. He admits it’s very individual and can involve a bit of trial and error. “The first thing I would do is try to increase weight a little bit and see if that helps,” he says. Maybe that means increasing your calorie intake by 250 calories per day or toning down your high-intensity workouts. “For some, 5 pounds would make a difference and return the menses,” Thoppil says.
Dr. Petre suggests staying close to the maximum amount of carbs you’re able to eat each day while maintaining ketosis (it’s different for everyone, but usually between 20 and 50 grams). Or she says to consider keto cycling, which involves keeping your body in ketosis for five days followed by two days of higher carb intake.
How long it will take to return to normal depends on when you settle into that threshold weight. “It could be as soon as within the month,” Thoppil says. “But everybody’s body is different in how they respond and what they need for adequate nutrition.”
How Keto May Also Help Periods Return
Interestingly, just as having success on keto can make your cycle disappear, the reverse may also be true: Overweight people who lose weight on keto may see periods return. “Weight gain often leads to difficulty with ovulation,” Thoppil says. “There are probably people who resume menses because they’re ketogenic.” In fact, he says there are likely just as many people who fall into this camp as those who lose their cycle.
A Final Word of Caution About Keto and Your Period
Keep in mind that your diet may not be to blame at all. Missed periods can be a sign of a larger health issue, such as hormone imbalance, genetic abnormalities, or polycystic ovary syndrome (PCOS), according to the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Kizer says losing your cycle — on keto or otherwise — is a good reason to visit your doctor.