April 18 2019

Keto and the Menstrual Cycle: Is There Reason To Worry?

By Lindsay Taylor, PhD
21 Comments

It seems every “keto for women” forum abounds with stories about menstrual cycles gone wild in the first few months of keto. Irregular cycles, breakthrough bleeding, and periods lasting much longer than normal are common complaints. Sometimes these stories are cited as evidence that keto isn’t good for women, at least not premenopausal women, and that we need carbs for healthy hormones. Yet, many women don’t notice any changes in their menstrual cycles at all, while others report improvement in PMS symptoms and cycle regularity from the get-go.

What gives? Why do some women’s cycles apparently become wacky when they start keto, while others feel like keto is the key to period bliss? Can keto “mess up” the menstrual cycle?

We know that diet—what and how much we eat—can profoundly affect our hormones. This is true for both women and men. One of the reasons people are so excited about ketogenic diets is specifically because keto shows promise for helping to regulate hormones and improve cellular sensitivity to hormones such as insulin and leptin.

At the same time, women’s hormones are especially sensitive not only to dietary changes but also to downstream effects such as body fat loss. Furthermore, one of the ways women’s bodies respond to stressors is by turning down the dial on our reproductive systems. It’s reasonable to hypothesize, then, that women might have a tougher time adapting to or sustaining a ketogenic diet. Keto can be stressful depending on one’s approach, and that might negatively impact women’s reproductive health. But do the data actually bear that out, or is so-called “keto period” more misplaced hype than genuine fact?

Note that throughout this post, I’m going to use the term “reproductive health” to refer to all aspects of women’s menstrual cycle, reproductive hormones, and fertility. Even if you aren’t interested in reproducing right now, your body’s willingness to reproduce is an important indicator of overall health. When your reproductive health goes awry—irregular or absent periods (amenorrhea) or hormone imbalances—that’s a big red flag. Of course, post-menopausal women can also experience hormone imbalances that affect their health and quality of life (and low-carb and keto diets can be a great option for them).

Menstrual Cycle 101

Let’s briefly review what constitutes a normal, healthy menstrual cycle, understanding that everybody’s “normal” will be a little different. A typical cycle lasts from 21 to 24 days on the short end to 31 to 35 days on the long end, with 28 days being the median. Day 1 is the first day of your period and begins the follicular phase, which lasts until ovulation. Just before ovulation, levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), and estradiol (a form of estrogen) spike. Next comes the luteal phase covering the approximately 14 days from ovulation to menses. LH, FSH, and estradiol drop, while progesterone rises. Estradiol bumps up again in the middle of the luteal phase. If a fertilized egg is not implanted, menstruation commences, and the whole cycles starts over again. All this is regulated by a complex communication network under the hypothalamic–pituitary–gonadal (HPG) axis, which is closely tied to the actions of the adrenal (the A in HPA axis) and thyroid glands.

Across the cycle, fluctuations in body weight are common as fluid is retained and then released along with shifts in estrogen and progesterone. Changes in blood glucose are also normal, and insulin-dependent diabetics often find that they need to adjust their dose at different times of their cycles to keep their blood sugar in check. The most common pattern is higher blood glucose readings in the pre-menstrual period (the second half of the luteal phase), and lower readings after starting your period and before ovulation. This is generally attributed to the fact that progesterone, which is highest during the luteal phase, is known to reduce insulin sensitivity. However, different women experience different patterns, which can also be affected by other factors such as oral contraceptive use.

Normal fluctuations in insulin resistance and blood glucose can mean that women get lower ketone readings at certain times of the month than others. When these occur premenstrually—and so they tend to coincide with a period of (transient) weight gain and food/carbohydrate cravings—women often feel as though they are doing something wrong. Rest assured that these variations reflect normal physiology.

The many factors that affect your cycle and the levels of your sex hormones include: other hormones, gut health and microbiome, metabolic health (e.g., insulin sensitivity), environmental toxins, stress, sleep, immune health, nutrient deficiencies, activity level and energy expenditure, and age. Each affects the others, and all (except age of course) can be affected by diet. It’s no surprise, then, that it can be extremely difficult to pin down a root cause of menstrual changes or reproductive issues.

What the Research Tells Us About Keto and Menstruation

As I said at the outset, there are lots of anecdotes, both positive and negative. In my experience, most women whose cycles seem to go crazy when they start keto find that things get back to normal—and often a better version of normal—after a few months.

First, it’s tricky to determine the effects of keto per se, since many people combine a ketogenic diet with calorie restriction (intentionally to lose weight or unintentionally due to the appetite suppressing effects of keto) and with fasting (intermittent and/or extended). Each of these can independently impact the factors listed above, lead to weight loss, and affect the menstrual cycle and reproductive health.

So, is there any evidence that keto itself causes changes to menstruation?

The scientific evidence is scant….

The one statistic you’ll see floating around the interwebs is “45% of (adolescent) females experience irregular menstrual cycles on keto.” This statistic comes from one small study of adolescent girls using a therapeutic ketogenic diet to treat epilepsy. Six of the twenty girls reported amenorrhea (loss of period) and three were diagnosed with delayed puberty. However, the ketogenic diet used for epilepsy is different and usually much stricter than an “everyday” keto diet needs to be, and epilepsy is frequently associated with menstrual dysfunction regardless of diet.

To extrapolate the findings of this study and argue that nearly half of teenage girls (or women generally) are likely to experience menstrual problems from going keto is a huge leap.

The fact is, I’m unable to find any studies done in healthy human females (or mice for that matter) demonstrating that otherwise normal menstrual cycles are disturbed by going keto.

5 Ways Keto-Related Factors *Might* Affect Your Menstrual Cycle

With the limited amount of research looking directly at keto and menstruation, let’s look first at whether there are direct effects of carbohydrate restriction or elevated ketone production on the menstrual cycle. Those are the defining characteristics of keto and what differentiates keto from other ways of eating. Then we can examine indirect effects that occur due to factors such as weight loss. These are not unique to keto, though they might be more likely on a ketogenic diet compared to other ways of eating.

Carbohydrate Restriction

There is no real body of evidence that looks at ketogenic levels of carb restriction and menstruation, but there are some clues. In this small study, functional hypothalamic amenorrhea (FHA) was associated with dietary fat restriction; women with FHA actually ate non-significantly more carbs than matched controls and nearly identical total calories. Likewise, in this small study, FHA was associated with lower fat intake but no significant difference in carb intake.

This meta-analysis looked at the effect of low-carb (not keto) diets on markers of reproductive health among overweight women. The researchers found four studies that examined effects on menstruation; all showed improved menstrual regularity and/or ovulation rates. Of six studies that looked at levels of reproductive hormones, five reported significant improvements.

Carb restriction also results in decreased insulin production. Hyperinsulinemia and insulin resistance are frequently associated with polycystic ovarian syndrome (PCOS), one of the leading causes of female infertility and a frequent cause of menstrual irregularity. There is currently a lot of interest in using keto to treat PCOS, but only one small study has so far directly tested the effectiveness of a ketogenic diet to treat PCOS, with positive results.

Ketones

No studies have looked at the direct effects of ketones on menstruation.

Weight Loss

Of course weight loss is not unique to keto, but keto can be very effective for weight loss. Some women experience rapid weight loss when first starting a keto diet. Weight loss in and of itself can impact menstruation through a variety of pathways. A key way is by reducing the hormone leptin. Leptin’s main job is to communicate energy availability to the hypothalamus—high levels of leptin tell the hypothalamus that we have enough energy on board, which also means we can reproduce. Low leptin can disrupt the menstrual cycle and is linked to hypothalamic amenorrhea.

Body fat loss can also affect estrogen levels since estrogen is both stored and produced in adipocytes (fat cells). While fat loss in the long term will decrease estrogen production, it is possible that rapid fat loss might temporarily raise estrogen levels and can also affect estrogen-progesterone balance. These transient changes in estrogen levels might underlie some of the menstrual irregularities women report.

Stress

Stress can impact the menstrual cycle in myriad ways. Cortisol acts on the hypothalamus and pituitary glands, affecting hormone levels, sleep, immune function, and gut health, to name a few. Diets can be a source of stress, both at the physiological and psychological levels. Keto has a reputation for being especially stressful because it is more restrictive than other low-carb diets, but this can be mitigated by following the Keto Reset tips for women.

Thyroid Function

Thyroid dysregulation is another common cause of menstrual irregularities, and there remains a pervasive belief that keto is bad for thyroid health. Indeed, the thyroid is sensitive to nutrient deficiencies and caloric restriction, and thyroid hormones, especially T3, do frequently decline on keto. However, as Mark has discussed in a previous post, changes in T3 levels might not be a problem, especially in the absence of other problematic symptoms. Moreover, many practitioners now use keto as a cornerstone in their treatment of thyroid disorders.

What Should I Take From These Findings?

The first takeaway: there just isn’t much direct evidence about how keto might affect your menstrual cycle, positively or negatively. We have some studies suggesting that low-carb diets improve some aspects of menstruation and reproductive health, but keto is more than just another low-carb diet. Ketones themselves have important physiological properties, such as being directly anti-inflammatory, which might positively impact women’s reproductive health.

Second, the ways that keto is likely to (negatively) affect menstruation aren’t unique to keto, they’re common to any diet: hormone shifts mediated by energy balance, stress, and weight loss.

Furthermore, since keto is so often combined with caloric restriction, time-restricted eating, and fasting, even the anecdotal evidence might not be able to tell us all that much. If a woman is eating ketogenically, in a big caloric deficit, and doing OMAD (one meal a day), and her leptin plummets, how are we to know what really caused it? We don’t have good evidence that otherwise healthy women start a well-executed ketogenic diet and end up messing up their menstrual cycles.

That said, women do need to be cognizant of the sum total of the signals they are sending their bodies when it comes to energy availability and stress. A lot of women come to the keto diet with a history of adrenal, thyroid, metabolic, and reproductive issues. It’s important that they’re extra careful about how they approach keto. Done correctly, it might be just what the doctor ordered. I encourage any woman who’s dealing with other hormonal issues to work with a medical practitioner to tailor a keto diet to her unique needs.

But I’m Telling You, Keto Made My Period Go Haywire!

Ok, I believe you, really! But changes do not necessarily equal dysfunction. It is normal to experience hormone fluctuations when you make a massive—or even a relatively small but important—shift in your nutrition. Sometimes those fluctuations are unpleasant or unwanted, such as a period that lasts 14 days or one that arrives a week before you planned while you’re on vacation. However, that doesn’t make them bad from a health perspective. We need to respect that our bodies are dynamic systems. Changing the input will invariably change the output, and the system might need a few months to adapt to a new normal.

If your cycle goes wonky but you’re otherwise feeling good, give it a few months to sort itself out. If after a few months it’s still all over the place (or definitely if you’re having other disruptive symptoms), enlist help. In the meantime, check to make sure you’re not short-changing yourself nutritionally or calorically. Scale back on fasting efforts, and consider shifting more toward a traditional Primal way of eating.

At the end of the day, if you go keto and experience negative effects, stop. Keto is super hyped right now, but if your body is sending you clear signals that keto is not a good approach for you at this time, don’t do it. You can always try again later. It might be that your first attempt at keto didn’t work, but with a few adjustments and some experimentation over time you can find a version of keto that works for you.

Thanks for reading, everyone. Do you have comments, questions, or feedback? Let me know below.

References:

Comninos AN, Jayasena CN, Dhillo WS. The relationship between gut and adipose hormones, and reproduction. Human Reproduction Update 2014; 20(2): 153–174.

Fontana R, Della Torre S. The Deep Correlation between Energy Metabolism and Reproduction: A View on the Effects of Nutrition for Women Fertility. Nutrients. 2016;8(2):87.

Klok MD, Jakobsdottir S, Drent ML. The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review. Obesity Reviews 2007;8(1):21-34.

Meczekalski B, Katulski K, Czyzyk A, Podfigurna-Stopa A, Maciejewska-Jeske M. Functional hypothalamic amenorrhea and its influence on women’s health. J Endocrinol Invest. 2014;37(11):1049–1056.  

Tena-Sempere M. Roles of Ghrelin and Leptin in the Control of Reproductive Function. Neuroendocrinology 2007;86:229-241.

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21 thoughts on “Keto and the Menstrual Cycle: Is There Reason To Worry?”

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  1. I think that IF these stories are true, as opposed to the latest hysterical attempt to discredit the “keto diet”, they are likely coming from women who have made a sudden, extreme change in their diet. I think that ketogenic diets are best approached gradually. For everyone, not just women.

  2. Here’s my anecdotal 2c worth. When I was doing strict paleo/primal (keto, I guess), my normally very predictable periods went haywire. Long, missing, short, spotting, you name it. But it turns out I was perimenopausal, so I don’t really know if things would have been weird regardless. Too many variables.

  3. Good overview. I am a functional dietitian who has been eating a Paleo diet for 5 years – so keto is not a huge shift in diet- and had Periods like clockwork every 28 days… Until I started keto and IF, not restricting calories but practiced mindful eating. I didn’t see more than a couple pounds of weight loss in those months but started having shorter cycles- over several months I got to a 12 day cycle and hair was falling out! Thyroid was ok. I thought I was perimenopausal but when I added back more carbs (followed Mark’s keto reset book at 50g CHO) and fasted less frequently, things started to shift back to normal (currently a 25 day cycle). I love keto and I love IF but I do think women should use caution and find their carb “sweet spot” to avoid hormonal changes if their hormone levels are already optimal. Also recommend limiting longer fasts to a couple times a week plus 12 hr overnight fast every day.

    1. The Adrenals back up the Ovaries in production of hormones. If the Adrenals are damaged and can’t back up the hormone production required, your menstruation goes haywire. Also, Keto dumps a ton of fat-soluble vitamins down the drain and it is important to consume these in larger quantities daily until your liver can catch up. And on top of that you need ALL trace elements and esp. IODINE in a plant form such as sea kelp DAILY. This will heal the endocrine system responsible for the hormone communication and production. It is NOT a lack of starchy carbs or fruity fructose carbs, it’s the result of a damaged/nutrient deficient endocrine system (adrenals included) that can’t deal with any more loss of ANY nutrient, which Keto does. This is why Keto gets such a bad rep.

  4. To be honest I’ve never heard this rumor. But I have heard the rumor over and over again that women have used keto to fix infertility issues, especially those, like me who suffer from PCOS. I think when women have been duped into starvation dieting of the low fat kind for generations, and then one of them suddenly reverses that, you’re bound to have an effect on hormones. The extremely low fat diets popular now also have an effect on the menstrual cycle and men’s sex hormones. Take it from someone who was vegan in the 1990s, it was never as low fat as it is today. The low fat, low protein craziness is what drove me to finally read Dr. Atkins. So I suppose I should be grateful for the madness. I think if we’re looking for rumors that have validity, the PCOS rumor, and the “hey, I’m fertile again!” rumor are more likely to be true. Are they changes? Oh yes. Are they worrisome? Nope. Well, not unless you’re an IVF drug seller.

  5. First of all, thanks for talking about this! Here’s my experience…since going Primal, and gradually transitioning to Keto my cycles have improved. They became more regular with very little to complain about…no major mood swings, little to no cramping, and not any significant bloating. This is a definite contrast to my days as a vegetarian/vegan (and I was eating very clean then.) I think the increased fat intake, and animal fat in general, has been very beneficial. At the age of 52 I am starting to notice some irregularity, but that’s to be expected. I have yet to experience a hot flash or anything menopause related.

  6. Also wanted to add that fasting doesn’t really work for me. Sometimes it just kind of happens, and I feel great, but in general I get too hungry. Since my overall health is excellent I’m not trying to force the fasting or restricted eating window. I just listen to my body.

  7. Interesting factors to consider. I did have hormonal troubles trying to do Keto, but…. I did not ease myself into it , was in a stressful period of my life, and also attempting prolonged fasting (e.g. occasional 24 hr). As others have stated, I think that especially for women, Keto and fasting should should be done intuitively, listening to what is working for your body rather than following a strict, prescribed regiment.

  8. I’m surprised to hear so much fear of fasting by your readers, Mark. I mean, I don’t consider it “fasting” unless it’s longer than 24 hours. And unless someone has significant enzyme problems which were probably found in infancy, everyone’s hunger stops completely after 48 hours of fasting. Now, if you eat something, anything, even broth, after that time, some people will feel hunger instantly. But you just went through the things that most people say are ok for them. So how did this discussion turn into one about fasting instead of about women?

    FWIW, I cured PCOS with keto and so have several women I know. A young woman tried it on my suggestion and managed to save herself thousands in IVF treatments. Keto is extremely beneficial for women’s hormones. I think this rumor is mostly manufactured from the bad experience of a few people. That said, we don’t know anything hardly at all about women or their health. Women have been systematically ignored by science for hundreds of years. (The male lab rat effect.) So if something is wrong with keto and women, I wouldn’t expect a lot of answers from science on it.

    1. May I ask how old you are? I’ve never given keto a long enough try because I’m a stressed sugar addicted mother of 2 toddlers, but I would like to give it an honest try, and I do go days here and there with almost zero carbs without issue. I actually just had my longest cycle ever at 35 days which was super weird for me, so that’s why I’m interested in info about keto and female health.
      I also agree that it isn’t fasting if it’s shorter than 24 hours. Time restricted eating is the correct term for less than 24 hours.

      1. If you are a stressed mom of 2 toddlers, make your dietary changes gently and slowly, so as not to add to your stress! Switch out sweetened drinks for water, use nuts for snacks – start with changes like that. Make new habits,
        And I would be cautious about fasting with toddlers, as you can get hangry…

      2. Oh Mama, I feel you! I am mother to just one toddler and I can’t even imagine two!!!!

        My personal experience is that if I have any sugar at all (that includes most fruit) then I am much less stable emotionally. Little things can make me just totally snap, and as you know, toddlers are the masters of the little things. I’ve found that after I have been off all sugar for several days – usually at least 3 – is when my emotional stability comes back and I am so much more tolerant and cheerful. It feels so much better.

        The hard part of course is getting through those three days, when your head is exploding and you need something sugary (for me it’s chocolate…) RIGHT NOW to keep your sanity intact. I have found that a cup of decaf coffee/tea with cream in it is a great substitute, because it’s warm and soothing and a little decadent, and it fills that hand-to-mouth motion that’s so comforting. Other snacks like nuts, cheese, meats, etc might also do it for you. But if you decide you’re going to try to kick that sugar dependency, have some alternatives planned out ahead of time, so you don’t have to think when you’re in crisis mode.

        Marge suggested making the changes gradually, which is a good place to start as far as making new habits, but I know that at least for me, to still have any sugar in my diet will never give me that emotional release that going completely cold turkey eventually gets for me. I still trip up of course, but each time is a smaller speed bump and I am able to make the choice to not have sugary stuff a lot of the time because I like feeling good and I know what a pain it is to dig out of the hole again.

        Good luck, and don’t beat yourself up when you trip! 🙂

        1. Also I wanted to add that for me, at least, starches don’t have that effect. If anything, having some starch is good for my mood. It’s just the sugars that make me happy in the short run, and crazy in the long run…

  9. As a woman with PCOS (with a normal BMI and without insulin resistance, but still meeting Rotterdam criteria with cysts on my ovaries, irregular cycles, and signs of high androgen levels), I’ve found eating more fats and fewer carbs is particularly helpful for regulating my cycle, but like anything, it takes a gradual changes. Even traveling can change my context, behaviors, and diet too drastically resulting in intermenstrual spotting, a very long cycle, or extended periods of bleeding. What has been helpful for me has been thinking of my lifestyle in terms of adding more fats to what I eat rather than cutting out carbs and not doing too much too soon, especially if weight loss is not a goal. Anyway, I appreciate this article as I’ve experienced very irregular periods and have often been confused with my own diagnosis of PCOS as I don’t have the associated metabolic factors such as high insulin levels or a high BMI (mine is 20 and has not changed significantly over the years). For me, just eating more fats (without doing too much too soon) has definitely helped with regulating my cycle independent of weight loss demonstrating that the composition of one’s diet can affect hormone levels. I don’t eat a ketogenic diet every day but rather, I’ve gone in and out and have tried to do so without drastically fast changes to my diet. Obviously, take my experience with a grain of salt as I’m one person, but I think that being gentle and kind with one’s body as well as changing the composition can work synergistically.

  10. I really appreciate this article for the reminder of the many variables we have to deal with as women. Our stories are all so unique which backs up the idea that there is no one size fits all. I’ve diipped in and out of keto and find it had no impact on my cycle, if anything I get less PMT. I’m 47 so likely approaching perimenopause. I have no symptoms yet but there’s no way to know if this is due to my diet. The challenge for me is to really pay attention to myself and to learn what works best for me. When we are stressed and juggling lots of things it’s hard to do this.

  11. Premenopausal here. No big deal going keto, I like IF, just can’t do it as long just before my period. Keto is awesome.

  12. Thank you so much for your article. On my end, I went keto by accident and found plenty of positive health effects including less painful periods BUT though my periods became less painful, they stopped listening to my birth control pills and have been coming about every 2 weeks. This has been going on for almost 5 months now and of course has worried me immensely. I have changed my birth control pills and also adjusted my keto diet (I realized that I was consuming too few fats) and I do hope that in a month or so, my menstrual cycle will stabilize again.

    1. Hi Christina, I have just started keto and this has happened to me also 2 weeks in. I’m not surprised as I’ve had break through bleeding in the past. I do worry about the contraceptive efficacy though – I have three kids and don’t want another!

  13. I’ve been on more a for about a year and a half I’ve stopped having “periods” I still get moody and little cramps. But for the last week or so my breast have been super sore. Touch or just normal bounce during walking. I’ve been crampy along with the sore breast but not the same cramps as I usually get. Any ideas?

  14. Hi. I’m a little confused as to what to do regarding my birth control pill while on keto. I’ve been on the pill for 10+ years and have always started my period 2-3 days into the sugar pill week. Now that I have been on keto, I get my period in the middle of my pack! When this happened for the first time I just continued to take my pill all the way through but then I had my period for like a month. Last month I decided to stop my back when my period randomly started and treat that week as my sugar pill week even though it was not time yet. Does anyone have any advice on this? I also really don’t want to get pregnant. Thank you!

    1. Marielle, I would discuss the change with your doctor. You might want to consider upping your carbs for a while to 80-90 grams/day for a while and then slowly decrease toward 50 again to see if that takes care of the issue. And in the meantime, I’d use a backup method for birth control. Best — M