Hormonal naturopathic doctor and The Hormone Boost author Natasha Turner, ND, listened intensely as a female patient sat across from her, lamenting on her struggles with maintaining a healthy weight. “I’ve been doing keto for months and at first, the weight was falling off me so easily. But now I’m gaining it back. I have no idea what happened!” Dr. Turner recalls the woman saying.
Dr. Turner wasn’t surprised. Ever since the ketogenic diet exploded in popularity, she’s been fielding complaints like this on a regular basis, primarily from her female patients. “I’m seeing a consistent trend of women adopting the ketogenic diet and the majority of them do not lose weight,” she says. She says she’s seen lots of patients who end up gaining unwanted weight, losing muscle, and developing signs of adrenal fatigue while on the buzzy eating plan.
This isn’t just something “keto haters” are warning about. A study published last year in the journal Diabetes (and recently presented at a conference) points to this potential downside, too. When researchers looked at how the ketogenic diet affected male and female mice, they found that while the male mice in the study lost weight, female mice ended up gaining weight. They also developed impaired glucose intolerance, a sign of prediabetes.
Of course, mice are very different from humans—so these findings don’t automatically mean that the ketogenic diet will mess with all women’s blood sugar levels and weight. But hormonal experts like Dr. Turner and others say that while many women may experience short-term success on keto, it may also have some sex-specific downsides. Why? Blame your hormones.
Drastically reducing carb intake can put stress on the body
Carbs have been painted as the devil, but all three experts I spoke to said that carbohydrates are a key part of women’s health. Not only do they contain crucial vitamins and nutrients like fiber, but the female body in particular needs a good amount carbohydrates along with fats and protein in order to sustain healthy hormone levels, says Aimee Raupp, MS, LAc, a licensed herbalist and acupuncturist specializing in fertility. “When we [as women] don’t get those complex carbs, we have a shift in serotonin levels, a shift in progesterone, and shift in insulin metabolism. All of that in turn affects our health and can make insulin levels go up and cause us to gain weight,” adds integrative health expert and Superwoman Rx author Taz Bhatia, MD.
According to Dr. Turner, cutting carbs very drastically can cause an increase in cortisol—the “stress” hormone. “According to the keto rules, followers are [usually] only allowed 30 grams of carbs a day from green vegetables. No starchy carbs. No fruit,” she says. (Some variations, like the ketotarian diet, do allow for some fruit and more relaxed carb macros). “This puts stress on the body, which raises cortisol levels.”
Why does this happen? Dr. Turner says that while in theory, people on the ketogenic diet burn fat for energy, it can actually dip into the body’s protein reserves because some people need more protein than what’s allowed for on the diet’s ratios. “You have to consume a minimum amount of protein to preserve your muscle mass,” she says—about 46 grams of protein a day for the average sedentary woman, although very active women need even more. Burning protein for energy instead of fat or carbs causes stress on the body, Dr. Turner says, spiking cortisol levels.
When cortisol levels are high over long periods of time, the body compensates by producing more testosterone and estrogen, and less progesterone. This hormonal change could cause problems like acne and missed periods, or worsen existing conditions like endometriosis or PCOS, says Raupp. While men and women can see their cortisol levels spike from cutting carbs, Dr. Bhatia says women tend to be more sensitive to changes in cortisol levels because our hormonal balance is more complex.
Plus, if people are doing keto over long periods of time, Dr. Turner fears that they could be putting themselves at risk for insulin resistance and prediabetes, which could ultimately lead to type 2 diabetes and other health issues. Why? Because elevated cortisol levels have been associated with those health issues. “The same thing happens when you wake up in the morning after not getting enough sleep,” she says. “Being sleep-deprived makes you have higher levels of cortisol, and it’s proven that those patients are more insulin resistant and have more glucose intolerance. It’s also related to change of cortisol levels.”
The high fat-hormone connection
Dr. Turner says another factor at play with keto is all of the fat. She says a diet high in fat spurs more estrogen production, which is also linked to weight gain (at least in mice). “Higher estrogen levels suppress the thyroid in women, which can lead to weight gain,” she explains.
Basically, the thyroid controls the metabolic process, which is the control system for weight management, energy levels, sex drive, concentration, and mood. When estrogen levels go up, thyroid activity goes down in attempt to balance it out. Likewise, when estrogen levels go down—such as during menopause, the thyroid goes up. It’s a very delicate dance.
“It’s a triple whammy,” Dr. Turner says of the keto diet. “One is that it increases your risk of having high cortisol because of the carbohydrate restriction. Two, it’s going to increase the production of estrogen because of the high fat diet. And three, these two changes—the high cortisol and high estrogen—suppress your thyroid and makes you more prone to weight gain.”
Dr. Bhatia agrees. “The reason why this is so critical for women is because the thyroid regulates so many other hormones,” she says. “Women’s hormonal systems are so delicate that doing anything to the extreme stresses the hormones, whether it makes you estrogen dominant or thyroid resistant. This is why women will maybe initially lose weight, but then plateau or even gain weight.”
What it could mean for fertility
Beyond weight, the ketogenic diet could have some serious consequences for fertility, says Raupp. “A menstrual cycle and optimal fertility is a luxury that the body imparts when it has enough to sustain itself,” she says. “When the body doesn’t feel like it can sustain itself, the hormones that impact fertility and menstruation will be compromised because the last thing on its list is to support and nourish another life if it can’t support and nourish its own life.”
Raupp says the strict macros on keto (particularly when combined with intermittent fasting) can create exactly this situation. “You are growing a human, or trying to, and going extremely low-carb or going for longer periods of time without eating tricks the body into a state of chronic stress,” she says. Hence the above-mentioned cortisol spikes, which subsequently suppresses the hormones that support fertility.
While keto advocates often claim that the eating plan can help balance hormones and can be used to manage conditions like endometriosis and PCOS (there are small studies that back this up), Raupp says she’s not convinced. “I’ve been in clinical practice for 15 years and the only thing I have ever seen work for balancing hormones is eating a nutrient-dense diet filled with healthy carbs, fats and protein,” she says.
Of course, some women really do claim to enjoy benefits and long-term success on the ketogenic diet. Dr. Turner says the jury is still out on how beneficial the eating plan will prove to be over time for women or men—as of yet, there’s no study out there yet that has extensively looked at the potential sex differences of the keto diet in humans. This is one case where time will tell. That is, if a whole bunch of let-down women don’t first.