When it comes to health and nutrition, we can all agree on some core fundamentals: Eat whole foods, move your body, get sufficient sleep, and take time to unwind. However, the truth is that we’re all different and have different physiological needs — particularly between biological men and women. Take intermittent fasting, for example. While a great nutrition strategy for most people, the science shows that there are some nuances to how fasting can affect the female body.
So, how can women optimize their fasting practice to account for these nuances and get awesome results? Read on for a deeper dive into fasting for women.
What Is Intermittent Fasting?
Intermittent fasting is an eating pattern that alternates between fasting (not eating) and eating on a specific schedule. Unlike diets that dictate what to eat, intermittent fasting focuses on when to eat. The goal is to lengthen the amount of time you naturally spend in the fasted state so that your body will burn fat (stored in your body), rather than carbohydrates (which you’d ordinarily eat), for fuel. Every human fasts while they sleep, but a compelling body of evidence suggests that lengthening your fast can yield tremendous health benefits. Adding even just a few hours to your daily fast can help you live a longer, healthier life.
What Are the Benefits of Intermittent Fasting for Women?
When it comes to the potential to improve health and longevity for women, intermittent fasting has earned its place in the spotlight. Studies show that intermittent fasting is one of the most effective ways to burn fat, lose weight, reduce your risk of cancer, and improve your metabolic health. And there are additional benefits, too!
Improved Body Composition
Intermittent fasting doesn’t just help lower the number on the scale; it helps you preserve lean mass (i.e., muscle) as you shed fat. Retaining muscle is supremely important as you age — it keeps your metabolism revved, reduces your risk of injury, and increases your overall quality of life. These benefits are even more important for women because they typically have less lean body mass and are at a higher risk of falls and falling-related injuries in old age in comparison to men. Research also shows that preserving lean body mass can help lessen the effects of menopause, from night sweats to weight gain!
You’ve likely heard of chronic inflammation, i.e. your body’s immune response to excessive stress. Triggers include everything from too little recovery to too many highly-processed foods. A high level of chronic inflammation is a major contributor to weight gain, most types of cancer, and PCOS. Fortunately, intermittent fasting (as well as simple, restorative practices like meditation or yoga) can help by quelling the release of proinflammatory cells, thereby reducing inflammation.
Better Mental Health
Mental-health disorders, including depression, anxiety, and Alzheimer’s, disproportionately affect women — but fasting can help. Intermittent fasting stimulates the production of a peptide called brain-derived neurotrophic factor (BDNF), which occurs in response to low glucose levels (which happen when you’re not eating) and ketone formation (which happens in response to fasting). BDNF supports your psychological well-being by protecting the neurons in your brain from damage and encouraging the growth of new neurons.
Fewer “Hangry” Episodes
Anyone — male or female — can get grouchy when it’s been too long since their last meal. However, data show that women report higher hunger levels and food cravings than men, even when controlling for restrictive eating. Fasting may seem like a counterintuitive solution, but research suggests it can make you less prone to bouts of hunger. One study showed that individuals who stuck to a 6-hour eating window reported less hunger and had lower levels of ghrelin (dubbed the “hunger hormone” because it increases appetite) than those who consumed the same number of calories over a 12-hour eating window.
Does Intermittent Fasting Affect Men and Women Differently?
Thanks to evolution, men and women possess several clear physiological and hormonal differences. Unfortunately, women have long been underrepresented in scientific studies, and studies surrounding intermittent fasting are no different. However, some research has been done to examine how intermittent fasting affects men and women differently, and from this research, the main takeaway is that prolonged fasts don’t serve women the same way they do men.
For one thing, longer or more aggressive fasts confer metabolic benefits for men that aren’t necessarily replicated in women. For example, a study examining the effects of alternate-day fasting (12 hours of normal eating followed by 36 hours of water-only fasting) showed improvements in glucose management and insulin sensitivity for men, but not women. This is important because when blood sugar levels are elevated long term (as the result of poor glucose management and insulin sensitivity), it can lead to serious health consequences including cardiovascular disease, obesity, and diabetes.
Also, fasting may affect women’s hormonal balance more than men’s, especially if it results in an energy deficit. Scientists are still working to understand the complete landscape, but the hormone kisspeptin, which is involved in the reproductive process, is a likely culprit. Kisspeptin is sensitive to nutrient availability. While both men and women have kisspeptin, women have higher levels of this hormone, and their levels drop more readily in response to fasting compared to men. Therefore, when women undergo prolonged fasts or fasts that result in cutting calories too aggressively, their kisspeptin levels can plummet — leading to a number of negative downstream hormonal effects, including loss of ovulation and monthly menstrual cycle. As a result, women may need to ease their way into longer, more aggressive fasts.
Another reason women may need to avoid or move more slowly towards longer fasts is that they are accompanied by a rise in cortisol. When your body is stressed, it releases the hormone cortisol. This response is not inherently bad; short periods of stress followed by recovery are a good thing. (The human body was designed to adapt and grow in response to these!) However, when stress is chronic and unrelenting and cortisol levels stay high, almost every system in your body suffers, from your heart to your lungs to your brain. Studies show that fasts longer than 48 hours cause dramatic increases in cortisol levels — and, according to some research, this stress response may be more exaggerated in women, putting them at greater risk of the negative consequences of cortisol.
What Is the Best Fasting Protocol for Women?
There is no “perfect” fasting protocol for anyone, including women. The strategy that will work best for you depends on your goals, your lifestyle, and unique physiology. For many women, a strategy known as time-restricted feeding, or TRF, is the preferred method. This strategy involves condensing the time when you eat so that you spend more time in a fasted state. Thirteen to 18 hours of fasting each day is a safe, achievable range for most women that is likely to yield a majority of fasting’s health benefits.
No matter how long you choose to fast, it’s a good idea to align your fasting window with your body’s natural circadian rhythm. This means eating your meals during the day and avoiding eating late at night. For example, if you are planning a 14:10 TRF schedule, eating between 7 a.m. and 5 p.m., as opposed to noon and 10 p.m., is the better way to go.
Fasting for Weight Loss
Women who have significant body fat to lose can typically handle a longer fasting window, such as a 16:8 or 18:6 TRF, and can even build up to longer fasting regimens, such as a 20:4 TRF.
Fasting for Premenopausal Women
For many premenopausal women, fertility is a major consideration. You may be hesitant to start fasting out of concern that it may negatively affect estrogen and reproductive health. This worry largely stems from the results of a study done on 3-month-old rats (equivalent to human age 12), which human studies have not replicated. For example, one study of women fasting for Ramadan showed that 14–16-hour fasts had no impact on fertility hormones. However, a more recent study examining the effects of 20:4 TRF on reproductive hormones showed that dehydroepiandrosterone (DHEA), a precursor to estrogen that is needed for egg quality, dropped. Therefore, if conception is your short-term goal, consult your OBGYN or a fertility expert before starting a fasting protocol.
When selecting a fasting protocol, something that gets very little attention — likely because the other half of the population doesn’t have to worry about it — is which phase of your menstrual cycle you are in. Varying your fast based on the phase you’re in can be beneficial and even protective of your health. Go easy during the later (luteal) phase of your cycle, which occurs just before your period starts when progesterone levels are high, and energy levels are often low. This is when your body is most susceptible to stress, so a 13:11 or no TRF during this phase may work well. During menstruation, it is okay to fast as long as you’re still prioritizing nutrient-dense foods, especially those rich in iron (due to blood loss). Fasting for 14–15 hours during this phase can be ideal. Save longer fasts for after menstruation but before progesterone peaks — days 7–21 for women on a 28-day cycle.
Fasting for Postmenopausal Women
Menopause brings about a changing hormonal milieu. Women entering this stage of life often gain weight — particularly around their abdomen — and see a decrease in insulin sensitivity. Research shows that intermittent fasting can be a useful tool in mitigating these changes and the associated increased risk of lifestyle diseases such as cardiovascular disease and osteoporosis. At the same time, loss of lean body mass is of even greater concern for women after menopause, so it’s important to choose an eating window that still enables you to get enough protein. If you are in perimenopause or postmenopause, 16:8 TRF fasts can be a good choice.
What Else Should Women Know About Intermittent Fasting?
Many of the negative effects that are associated with women and fasting, such as menstrual dysfunction, are actually due to insufficient caloric intake. Therefore, it’s important to consider your energy needs and body composition when choosing a fasting style. The closer you are to your ideal body weight or body fat percentage, the more conservative you should be with your fast. Extended fasting when you are too lean can have negative consequences, particularly for women; hormone dysregulation, low bone mineral density, and impaired fertility may result and should be avoided.
To put numbers to these recommendations: fasting or other methods of caloric restriction are not recommended if your BMI is below 18.5. Body-fat percentage is less straightforward, but studies indicate that women with body-fat percentages under 20% are at risk of hormonal irregularities, independent of fasting, and so it’s best to use a conservative fasting approach to avoid contributing to this risk. The same goes for if you are a hard-core athlete — be conservative to protect your health. If you want to fast most days of the week, a gentle fast, such as a 13:11 or 14:10 TRF schedule, is best.
Additionally, there are times when women should not fast. Fasting is not recommended if you are:
- Pregnant or breastfeeding
- Trying to become pregnant, except if you are overweight or obese
- Experiencing amenorrhea (loss of menstruation) or other menstrual dysfunction not due to being overweight or obese
- Diagnosed with an eating disorder, past or present
- Under the age of 18
For most women, intermittent fasting is a safe and effective lifestyle change that can reduce your risk of chronic disease and help you live a long and healthy life. However, because the female body is uniquely designed and goes through several hormonal shifts over a woman’s lifespan, there are more factors to consider when choosing how to fast. A more conservative approach can be best for regulating hormones, optimizing fertility, and preserving lean body mass, while a more aggressive approach might work well for women whose weight is undercutting their health.
The “right” fasting protocol for you depends on many factors, including your current physiology and your goals. Being thoughtful and intentional about how fasting affects you as a woman can help you stay healthy and live longer.