Hormonal naturopathic doctor and The Supercharged Hormone Diet ($16) 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. Dr. Turner says she’s seen lots of patients who end up gaining weight, losing muscle, and developing signs of adrenal fatigue while on the buzzy eating plan—opposite of what is promised to people who follow it.

Hold up, what’s keto again? Check out this video for all the need-to-know intel: 

This isn’t just something “keto haters” are warning about. A study published in 2018 in the journal Diabetes (and 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 pre-diabetes.

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 benefits on keto, it may also have some sex-specific downsides. Why? Blame your hormones.

How the ketogenic diet affects hormones in women

On the surface, the ketogenic diet sounds like a great plan for hormone balance. Advocates of it point to the fact that the eating plan champions healthy fats, which do exactly that. Cutting back on simple carbohydrates and reducing sugar intake are also both connected to supporting hormone health.

Dr. Turner is all in favor of minimizing sugar and simple carbs while upping healthy fat intake in the name of hormone balancing. She just thinks the ketogenic diet takes it too far. This is because, she says, the eating plan nixes many high-fiber foods, like starchy vegetables and whole grains, and fiber is key for hormone balance. “From what I have read, the keto diet does not favor enough fiber and, in fact, there is a link to digestive microbiome imbalance with this diet [at least in mice],” she says.

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,” Dr. Turner says.

And that’s not the only hormone cutting complex carbs affects.”When [people with uteruses] don’t get complex carbs, we have a shift in serotonin levels, a shift in progesterone, and shift in insulin metabolism,” says integrative health expert and Superwoman Rx author Taz Bhatia, MD.

These hormonal changes can cause problems like acne or worsen existing conditions like endometriosis or PCOS, says Aimee Raupp, MS, LAc, a licensed herbalist and acupuncturist specializing in fertility. It can also affect the menstrual cycle in a range of ways. Dr. Turner adds that some women may experience heavier periods and worse PMS because of the increase in estrogen. Other women may experience the complete opposite and their period may cease completely or come less often. If this happens, if could be a sign your body isn’t getting enough nutrients to function properly and it’s crucial to consult a doctor.

For women in perimenopause or menopause, the increase in cortisol and estrogen could make symptoms worse. “I do not recommend the ketogenic diet for women in menopause at all,” Dr. Turner says. She reiterates the importance of fiber and starchy carbs, also adding that protein is another nutrient women in perimenopause or menopause need to be especially mindful of; you want to up your intake of this nutrient. “This will help maintain muscle mass and prevent bone density decline,” she says.

While the ketogenic diet does prioritize protein, it does so while neglecting the complex carbs and fiber, Dr. Turner says are key for women in menopause (and truly all stages of life).

Drastically reducing carb intake can put stress on the body

As you can see, even though carbs have been painted as the devil, they’re a key part of women’s health. In fact, all three experts emphasize this. Raupp explains that when the hormonal balance is disrupted, stress is put on the body, which can then lead to weight gain. Dr. Bhatia cosigns this. “The shift in serotonin levels, progesterone, and insulin metabolism all can make insulin levels go up and cause us to gain weight,” she says. There isn’t anything necessarily wrong with weight gain, but if one’s goal on keto is for weight management, then this isn’t the desired outcome.

Remember how Dr. Turner pointed out that drastically reducing carbs can cause cortisol levels to go up? That puts stress on the body and can cause weight gain too. Dr. Turner says that while in theory, people on the ketogenic diet burn fat for energy (through a metabolic process called ketosis), 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. And remember, protein is especially important for menopausal women, so this can be especially detrimental for them.

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, thyroid activity increases. 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

The ketogenic diet could also 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.

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. Nor is there substantial long-term research on its effects in humans. This is one case where time will tell. That is, if a whole bunch of let-down women don’t first.

Oh hi! You look like someone who loves free workouts, discounts for cult-fave wellness brands, and exclusive Well+Good content. Sign up for Well+, our online community of wellness insiders, and unlock your rewards instantly.