Intermittent fasting (IF) for women is complicated. There is a lot of positive research behind intermittent fasting, so it's hard not to feel tempted to jump right in after hearing so many fasting success stories. But is it safe and effective for everyone?
My goal with this article is to present the facts behind intermittent fasting— the good and the not-so-good— so you can make an educated decision about whether fasting is a good choice for you. We'll explore all the ins and outs of fasting, from schedules to safety, how it impacts your hormones, period, libido, and more.
Most importantly, I want you to understand why intermittent fasting can affect women differently than men. So let's dive in!
What is Intermittent Fasting?
Intermittent fasting (IF) is a pattern of eating that alternates periods of fasting with set windows of eating. Unlike a typical “diet,” IF emphasizes the timing of your meals instead of what or how much you eat. It's not that food quality doesn't matter, but it's not the primary focus.
Fasting means abstaining from anything with calories. Water, herbal tea, and black coffee are okay because they don't contain calories (or they contain trace amounts). But anything with calories is off-limits.
While intermittent fasting seems to be the talk of all wellness circles, fasting itself is not new. It's been an essential part of spirituality and religion for thousands of years. Fasting has also been a part of the wellness world for a long time, but it's only relatively recently that it's become so mainstream.
Part of why it's so popular is that IF can be tweaked to work with your lifestyle. There's no one right way to do it, and in fact, there are many different ways to practice intermittent fasting (which you'll learn about below). It also may feel less restrictive than a typical calorie-controlled diet.
Intermittent fasting experts suggest that part of the reason that fasting is so beneficial is that it works with our natural physiology. IF proponents argue that we are evolutionarily designed to go for extended periods without food, although this is still debated.
Either way, by going longer without food, especially overnight, IF may help you reduce caloric intake (especially if you are prone to late-night snacking). But as you'll learn, some research suggests that fasting benefits extend beyond weight loss.
Intermittent Fasting Schedules
As mentioned, part of the reason IF is popular is that you can make it work around your schedule. There are many different ways to do it, and each has research suggesting its efficacy.
As an aside, I'm not necessarily promoting any of these as it’s a very individualized approach, but they are the ones you are most likely to hear about:
- The 12-hour fast. A very gentle version of fasting, the twelve-hour fast is usually safe for most people. It matches the natural pattern you'd probably follow overnight anyway, assuming you don't eat late at night, but it still can be effective. Finish dinner at 7 p.m.? Just have breakfast at 7 a.m.
- The 16:8 method. This method is one of the most popular ways to practice IF. You fast for 16 hours and eat during an eight-hour window. People like it because it just means pushing breakfast a few hours later than usual. For example, if you stop eating at 8 p.m., you'd fast until noon the next day.
- The 5:2 method. This type of fasting is known more as a fasting-mimicking pattern because you never go entirely without food. Calories are limited to 500 each day for two days a week, and then you eat as you usually would on the other five days.
- Eat-stop-eat.This pattern follows a 24-hour fast for a few non-consecutive days a week while eating normally the other days. So you'd fast for a full day, normally eat for the next few days, and then choose one more day to fast. 24-hour fasts aren't recommended for people just getting started (or really at all in most cases).
- Alternate day fasting. A pattern where you follow a fasting protocol like 16:8 or 14:12, but you don't do it every day. This method may be a better choice for women (you'll learn more about why later in the article). Some people choose to fast for a full 24 hours every other day with alternate day fasting, but again, I can’t recommend 24-hour fasting in most cases.
- One meal a day (OMAD). Just as it sounds, OMAD only allows one large meal a day or a very short eating window of four hours or less. Since it's so restrictive and sets many up for disordered eating patterns, I don't recommend this pattern.
How Does Intermittent Fasting Affect Women's Health?
Despite its popularity, we have to discuss the fact that most research on IF is conducted on men. Few studies account for differences in women’s biology (as is the case for a lot of medical research, unfortunately). And since women's physiology is so different from men's, it stands to reason that intermittent fasting could affect us differently.
One of the few studies that included both male and female subjects found that while IF was supportive for men, it impaired blood sugar responses for women.
Does that mean fasting is never a good idea for women? No, but there are specific people who should avoid fasting, especially long-term. For those who can follow IF safely, there are ways to implement fasting in your life that are compatible with women's biology.
Let's explore the general pros and cons of intermittent fasting for women.
The Benefits of Intermittent Fasting
The benefits of intermittent fasting stem not just from eating less (although this can happen when you shorten a window of food availability) but also from metabolic adaptations that occur when you go longer without eating.
The primary adaptation that happens during fasting is known as autophagy. Autophagy is your body's self-cleaning mechanism that switches on when nutrients are unavailable. Damaged or old cells are cleaned out to make room for healthier cells, protecting cellular and metabolic health.
Autophagy is one benefit of intermittent fasting, but there are also many more interesting research findings, including:
- Weight loss. Many studies point to the benefits of intermittent fasting for weight loss. Not only do you limit late-night mindless eating, but some research suggests that those following intermittent fasting patterns lose as much weight as people cutting calories without the feelings of deprivation.
- Increased fat burning. If you drop carbohydrate intake, your body turns to alternatives for fuel. After burning through your limited stored carbs, fat can be used instead. Some research has found that fasting increases fat burning by turning on the metabolic switch to use fat as fuel.
- Cognitive health. Fasting may support cognitive function, especially associated with age. It could help also slow down neurodegeneration, the progressive decline of cells in the brain, although primarily seen in animal studies.
- Longevity. Since autophagy may support cellular health by cleaning up old damaged cells, it can reduce oxidative damage and support healthy aging.
- Heart health. Fasting may also support healthy cholesterol, which influences your risk of heart disease.
- Blood sugar and insulin resistance. Fasting may support improvements in weight, insulin, and insulin resistance as effectively as a calorie-restricted diet.
- Immunity. Fasting may positively influence the production of healthy white blood cells through autophagy.
- Inflammation. Several studies have found that fasting improves markers of inflammation and oxidative stress.
The Side Effects and Risks of Intermittent Fasting
It seems like a no-brainer to add fasting to your daily habits with all these potential benefits and that is in fact the allure that has so many people jumping in. But there are a few things to consider before starting, especially for women.
Like any other significant change to the way you eat, you should talk to a health care provider before starting any type of fast. Even gentle fasting can carry risks, especially for people who have:
- A history of eating disorders or disordered eating habits.
- Diabetes or hypoglycemia, especially if you take medications that lower blood sugar.
- Trouble gaining sufficient weight or people working through nutrient deficiencies.
- A history of electrolyte imbalances, especially with longer periods of fasting.
It's not that you can't fast if you fall into any of these categories, but it makes it extra important to ensure you have the proper guidance to see if it's safe for you. I can’t stress enough, if you have a history of disordered eating or an eating disorder, it is best to discuss it with a qualified health practitioner before beginning. The potential risk may not outweigh the benefits.
In some cases, fasting should be avoided altogether:
- Pregnancy or breastfeeding.
- History of amenorrhea (missed periods) or concerns with fertility or missing ovulation.
- High stress or hypothalamic-pituitary-adrenal axis (HPA-axis) dysregulation (we'll look at this in a bit, but your HPA-axis is closely involved in your stress and hormone response).
Many of the reasons why fasting can be different for women stem from the impact of stress on women's hormones, which we will explore in detail below.
Additionally, there are a few reported side effects, but most of them are generally mild, including:
- Feelings of hunger
- Mood swings or irritability
- Fatigue and lightheadedness
- Increased cravings
But many of these symptoms can be helped with minor adjustments like how long you fast. That said, some people just don't feel well fasting, and that's okay too.
If you decide to fast, it's helpful to consider how to do so safely. Here are some steps you can take.
- Start slowly. If you've never fasted before, you don't want to jump into an extended fast. Start by simply extending the time between dinner and breakfast a bit longer than usual. Even ten hours is fantastic if you usually graze all evening. Since digestion as well as insulin function naturally slows as the day goes on, perhaps a good way to begin is to eat dinner one hour earlier than you currently do.
- Drink water. Fasting may mean you don't eat anything with calories, but calorie-free fluids like water and herbal tea are encouraged. Drinking enough water can help with feelings of headaches and hunger. Plus, we meet some of our total fluid needs through water-containing foods, so you may need to drink extra to make up for it depending on the length of your fast.
- Plan ahead. Have yummy, healthy foods ready to eat when you break your fast. Choose a meal that includes healthy fat, protein, and complex carbs for optimal blood sugar balance and set the tone for the rest of your meals. You can use are free hormone balancing recipe guide for inspiration.
- Keep physical activity light. Depending on how long you fast, you may want to back off the high-intensity exercise. Shorter fasts won't necessarily impact your ability to exercise, but walks or gentle yoga may make more sense if you try a longer fast.
- Listen to your body. Don't feel great while fasting? Don't force it. If you don't feel well, there's absolutely no reason you need to continue to fast. You know your body best. Repeat after me: Don’t force it.
How Does Intermittent Fasting Affect Your Hormone Balance?
Now it's time to jump into why intermittent fasting may not be as effective for women. Or why women may need to tweak the schedule a bit to see the same benefits.
Surprise— it's because of our hormones!
Many of the supposed metabolic benefits from fasting are due to how your body adapts to perceived stress. We often think of stress as only a negative thing, but some short-term stress can actually be good for us.
A great example is seen with exercise. When you lift weights, you put stress on your muscles, which in turn helps you get stronger. Fasting is similar. It's a type of stress that forces your body to use alternative fuel sources and move into autophagy to respond to nutrient scarcity.
But the female reproductive system is especially sensitive to stress. So much so that the hypothalamus will turn down the production of your reproductive hormones necessary for ovulation and menstruation when under stress.
Stress includes calorie and food restriction, and your hormones are very sensitive to how much food you put into your body. So if you regularly participate in extended fasts or one of the more restrictive patterns above, you may be overly stressing your body out and negatively impacting your hormone balance.
How and why does this happen? Gonadotropin-releasing hormone (GnRH), which stimulates the release of luteinizing hormone (LH) and follicular stimulating hormone (FSH) from your pituitary gland, is sensitive to stress, including fasting, even the short-term fasts.
LH and FSH play essential roles in your menstrual cycle and ovulation. Turn GnRH down or interrupt production, and estrogen and progesterone drop too.
There's some indication that another hormone may be involved called kisspeptin. Kisspeptin is part of the process to stimulate GnRH production, and it also appears to be sensitive to stress. Both men and women have kisspeptin, but women have more.
One animal study found that kisspeptin production goes down during fasting, which would turn off the production of estrogen and progesterone. While more research is needed, it could provide a clue for why women respond differently.
So what does all of this mean for women and fasting? Intermittent fasting can put stress on the body that negatively impacts hormone balance for some people. Hormone imbalances can lead to a cascade of unwanted symptoms, issues with your period, and even infertility.
Will this happen to every woman? No, but knowing it can occur can make it easier to decide if it's the right fit for you. And if you notice you start to have symptoms when you start, take it as a sign that it may not be working for your body.
Lose your period while fasting? Bail on the mission! That’s a clear sign this isn’t for you as the crucial vital sign that is your menstrual cycle is flashing you an alert warning. It’s not a good thing to lose your period—ever.
Does Intermittent Fasting Affect Estrogen Levels?
The downstream impact of these hormonal changes means that fasting could decrease estrogen production. While we often think of estrogen as a hormone primarily involved in reproduction and sexual health, it does so much more.
Estrogen is protective for our heart and brain health. It plays a role in mood, sleep patterns, metabolism, body fat, and insulin sensitivity. Disruptions in estrogen balance, either too much (known as estrogen dominance) or too little, can significantly impact your health and just make you feel terrible.
To be clear, if you think you have estrogen dominance, it’s best addressed with diet and lifestyle changes first (as I share in the linked article). Once you have a solid foundation, IF could be considered as an additional approach
Stress and undernutrition can lead to hypothalamic-pituitary-ovarian (HPO) axis dysfunction, adversely impacting estrogen balance. HPO-axis dysfunction leads to drops in LH which in turn affects estrogen production.
Research suggests that the HPO-axis disruption can occur when the body is under stress from undernutrition or over-exercise. It's part of the reason athletes often experience amenorrhea. Fasting could have similar outcomes if taken too far.
What About Other Hormones?
Other hormones may also be impacted by fasting. Thyroid hormones, which regulate metabolism and energy, may decrease during extended fasts, according to animal studies.
Some human studies have also shown changes in thyroid hormones. Still, many practitioners question whether this is actually a concern as thyroid hormones appear to return to normal once subjects start eating again. More research specifically on fasting and the thyroid is needed.
Like estrogen, progesterone production can also drop due to alterations in the HPO-axis and GnRH, throwing off overall hormone balance. If you are curious about the signs of hormone imbalance, I've written about it extensively here.
Intermittent Fasting and Your Period
A small study that followed 15 women with PCOS over six weeks found that fasting for 16 hours significantly improved body weight and other markers of insulin resistance and inflammation. While it was only a small study, it's worth noting that the authors noted that more than 70 percent of the women had improvements in their menstrual cycles.
However, another review found evidence that longer fasts increased cycle lengths in overweight or obese women. Three days of fasting also affected luteinizing hormone dynamics for women with regular menstrual cycles. This study concluded that while none of these changes were dramatic, more research is needed to understand exactly how caloric restriction during fasting impacts women's hormones.
Needless to say, the science behind fasting and your period is inconclusive and depends on many factors, but overdoing it with longer fasts or extensive calorie restriction may not be ideal for hormone balance.
Intermittent Fasting and Menopause
Menopause and the years leading up to it are characterized by significant shifts in your reproductive hormones. But once you are postmenopausal, meaning you haven't had a period for at least a year, your hormones usually remain relatively stable.
Menopause is also associated with many other changes in a woman's health, especially metabolic shifts due to declining estrogen.
During menopause, women often notice weight gain, especially around the abdomen. With the drop in estrogen, the risk for heart disease, insulin resistance, and dementia increases because, as you learned earlier, estrogen plays a protective role.
Intermittent fasting may help since many of the benefits of fasting tie closely with menopause-specific health concerns, including blood sugar balance, blood pressure, weight loss, fat burning, and lipid improvements.
As a result, even practitioners who usually don't recommend IF may consider menopause a better time to try it simply because postmenopausal women have much more stable hormones during this period of their life, so the potential impact on hormone fluctuations is lower.
Unfortunately, there really isn't any solid evidence specifically examining intermittent fasting during menopause. From my perspective, IF could be beneficial for postmenopausal women, but once again, it really depends on the individual.
Intermittent Fasting and Cortisol
Since fasting is a stressor, another hormone to consider is cortisol. Cortisol is your primary stress hormone, and it also contributes to elevated blood sugar and belly fat – both already a problem for many women during menopause.
While we don't necessarily have to worry about stress impacting a woman's menstrual cycle during menopause, stress is still a concern throughout our lifetime. And as you learned, there is some indication that fasting can reduce estrogen. Since estrogen is already low for postmenopausal women, this is another factor that needs to be considered in the big picture.
So easing into fasting, listening to your body, and being mindful of what other influences could exacerbate stress are all realistic to consider before fasting during menopause.
Intermittent Fasting and Your Libido
Once again (I know you are surprised at this point), the research is lacking on women, libido, and intermittent fasting. A study on men who fasted during Ramadan found fasting decreased their sexual desire and frequency of sexual activity, but studies on women are sparse.
Since fasting can impact hormone balance and potentially decrease estrogen, it could negatively affect sexual desire, but no studies expressly point to this. Fasting could also negatively impact your energy or mood if taken too far, which can decrease your desire to have sex.
On the other hand, if fasting works for you and you feel healthy or notice positive physical changes in your body, then it could help with libido. Weight and confidence in our bodies directly impact sexual desire, something backed by research, but also most of us have experienced first-hand. So for women who do well with fasting, a welcomed side effect could be improved libido.
Intermittent Fasting for Women Requires an Individualized Approach
Should you try intermittent fasting? It really depends.
Intermittent fasting has a lot of compelling, valid research behind it, but the data on women is mixed. Until we see more studies that specifically examine women in various phases of life, it's impossible to say that it's a good idea for all women.
That said, there are ways to make it safer and still see many of the benefits. Start with shorter fasts and keep fasting to no longer than 16 hours. Alternating days or only fasting a few days a week may also be a good idea, especially if fasting is brand new for you.
Pay close attention to how you feel, including mood, sleep, and cravings, as these are all indications that your current plan may be putting too much stress on the body. And, of course, if you notice any changes in your menstrual cycle, it's an indicator that your body is out of balance.
If you are considering fasting for hormonal support, it's worth trying to optimize hormone balance through a nutrient-dense meal plan like the one I offer in my free hormone starter kit. You can even follow these meals during your eating window if you choose to IF to make sure you are making choices to optimize your hormones at mealtime.
Intermittent fasting can be an effective wellness tool for some people, but if you are unsure if it's right for you, I suggest reaching out to your health care provider to get individualized support. And remember, as women, different seasons of our life call for different lifestyles. What works for you at one moment might not work for you in another. Learning to accept that we are dynamic beings as women is an important step towards feeling whole and bountiful! This shift in perspective is about being compassionate towards ourselves. All health starts there.
- Trepanowski, J.F., Bloomer, R.J. The impact of religious fasting on human health. Nutr J. 2010. 9.
- De Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2019. 2541-2551.
- Lim, K. Why is autophagy important in human diseases?. Exp Mol Med. 2012. 44. 69-72.
- Jamshed H, Beyl RA, Della Manna DL, et al. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019. 11. 1234.
- Heilbronn LK, Civitarese AE, Bogacka I, et al. Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting. Obes Res. 2005. 13. 574-581.
- Welton S, Minty R, O'Driscoll T, et al. Intermittent fasting and weight loss: Systematic review. Can Fam Physician. 2020. 66. 117-125.
- Harvie, M., Pegington, M., Mattson, M. et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes. 2011. 35. 714-727.
- Phillips MCL. Fasting as a Therapy in Neurological Disease. Nutrients. 2019.
- Metaxakis A, Ploumi C, Tavernarakis N. Autophagy in Age-Associated Neurodegeneration. Cells. 2018.
- Bareja A, Lee DE, White JP. Maximizing Longevity and Healthspan: Multiple Approaches All Converging on Autophagy. Front Cell Dev Biol. 2019.
- Ahmed N, Farooq J, Siddiqi HS, et al. Impact of Intermittent Fasting on Lipid Profile–A Quasi-Randomized Clinical Trial. Front Nutr. 2021.
- Barnoskya AR, Hoddyb KK, Untermana TG, Varady KA. Krista A.Varady. In-Depth Review: Excess Adiposity and Disease. Translational Research. 2014. 164.
- Cheng CW, Adams GB, Perin L, et al. Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression [published correction appears in Cell Stem Cell. Cell Stem Cell. 2014.
- Aksungar FB, Topkaya AE, Akyildiz M. Interleukin-6, C-reactive protein and biochemical parameters during prolonged intermittent fasting. Ann Nutr Metab. 2007.
- Johnson JB, Summer W, Cutler RG, et al. Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radic Biol Med. 2007.
- Sundfør TM, Svendsen M, Tonstad S. Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial. Nutr Metab Cardiovasc Dis. 2018.
- Watkins E, Serpell L. The Psychological Effects of Short-Term Fasting in Healthy Women. Front Nutr. 2016.
- Harvie M, Wright C, Pegington M, et al. The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. Br J Nutr. 2013. 1534-1547.
- Guelinckx I, Tavoularis G, König J, et al. Contribution of Water from Food and Fluids to Total Water Intake: Analysis of a French and UK Population Surveys. Nutrients. 2016.
- Collier R. Intermittent fasting: the science of going without. CMAJ. 2013.
- Nagma S, Kapoor G, Bharti R, et al. To evaluate the effect of perceived stress on menstrual function. J Clin Diagn Res. 2015. 9.
- Schneider JE. Energy balance and reproduction. Physiol Behav. 2004. 81. 289-317.
- Hill JW, Elmquist JK, Elias CF. Hypothalamic pathways linking energy balance and reproduction. Am J Physiol Endocrinol Metab. 2008. E827-E832.
- Iwasa T, Matsuzaki T, Yano K, Irahara M. Gonadotropin-Inhibitory Hormone Plays Roles in Stress-Induced Reproductive Dysfunction. Front. Endocrinol. 2017.
- Kumar S, Kaur G. Intermittent Fasting Dietary Restriction Regimen Negatively Influences Reproduction in Young Rats: A Study of Hypothalamo-Hypophysial-Gonadal Axis.
- Mendelsohn ME, Karas RH. The Protective Effects of Estrogen on the Cardiovascular System. N Engl J Med. 1999. 1801-1811.
- Zárate S, Stevnsner T, Gredilla R. Role of Estrogen and Other Sex Hormones in Brain Aging. Neuroprotection and DNA Repair. Front Aging Neurosci. 2017. 9. 430.
- Deborah J. Minireview: The Year in Review of Estrogen Regulation of Metabolism. Molecular Endocrinology. 2012. 26. 1957-1960.
- Stafford DE. Altered hypothalamic-pituitary-ovarian axis function in young female athletes: implications and recommendations for management. Treat Endocrinol. 2005. 4. 147-154.
- Boelen A, Wiersinga WM, Fliers E. Fasting-induced changes in the hypothalamus-pituitary-thyroid axis. Thyroid. 2008. 18. 123-129.
- Fontana L, Klein S, Holloszy JO, Premachandra BN. Effect of long-term calorie restriction with adequate protein and micronutrients on thyroid hormones. J Clin Endocrinol Metab. 2006. 3232-3235.
- Van der Valk, E.S., Savas, M. & van Rossum, E.F.C. Stress and Obesity: Are There More Susceptible Individuals?. Curr Obes Rep. 2018. 7. 193–203.
- Li C, Xing C, Zhang J, Zhao H, Shi W, He B. Eight-hour time-restricted feeding improves endocrine and metabolic profiles in women with anovulatory polycystic ovary syndrome. J Transl Med. 2021.
- Varady KA, Bhutani S, Church EC, Klempel MC. Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. Am J Clin Nutr. 2009. 1138-1143.
- Talib RA, Canguven O, Al-Rumaihi K, Al Ansari A, Alani M. The effect of fasting on erectile function and sexual desire on men in the month of Ramadan. Urol J. 2015. 2099-2102.
- Huhmann K. Menses Requires Energy: A Review of How Disordered Eating, Excessive Exercise, and High Stress Lead to Menstrual Irregularities. Clin Ther. 2020. 42. 401-407.