Intermittent fasting, an eating pattern that cycles between periods of fasting and eating (with the fasting period lasting at least 12 hours), is a common strategy for weight loss and improved metabolic health. While fasting is safe for most people, it can affect men and women differently due to factors like hormonal fluctuations, reproductive health, and life stage changes. Understanding how these factors influence fasting outcomes is important for women who want to incorporate fasting—and its many benefits—into their lives.
How fasting affects women differently
Men and women can experience many of the same benefits of fasting, which include:
Weight loss
Better blood sugar regulation
Reduced inflammation
Improved gut health and digestion
Lower cholesterol
Healthy blood pressure
However, women sometimes don't see as dramatic results as men. The main reason? Hormones.
Intermittent fasting and women’s hormones
Hormonal changes caused by fasting may differ from woman to woman, depending on the phase of the menstrual cycle she’s at, her hormonal profile, or her starting body composition.
But in general, during fasting, the sex-binding globulin hormone (SHBG) and dehydroepiandrosterone (DHEA) hormone might be impacted. SHBG helps to carry reproductive hormones (estrogen and progesterone) and affects their bioavailability, while DHEA helps produce other hormones (androgen and estrogen).
In addition, weight-loss interventions, which includes intermittent fasting, have been shown to reduce estrogen levels.
Lower levels of estrogen and progesterone can cause a variety of symptoms, including changes to menstrual cycle, moodiness, headaches, acne, and trouble sleeping. Hormonal variations during fasting can also cause more significant fluctuations in blood sugar levels during fasting compared to men, which is partly due to the role estrogen plays in regulating insulin sensitivity.
These hormonal variations affect women’s metabolic health overall, which is part of why women may not see the same results from fasting that men do.
Intermittent fasting tips for women
So is it only men who benefit from intermittent fasting? Nope! Women can get a lot out of intermittent fasting too, but it’s a good idea for them to approach it a little bit differently to minimize the disruption fasting can have on hormones.
Start slow. If you’ve never tried intermittent fasting before, start by fasting 12 hours a day. Once you’re comfortable with that, gradually add more time until you’ve extended your fast to 16 hours or a length you’re comfortable with.
Don’t go to the extreme. A realistic schedule you can maintain is best. Avoid the extreme intermittent fasting schedules, like alternate-day fasting (fasting every other day or fasting for 24 hours a few days a week) and the warrior diet (fasting or restricting calories for 20 hours a day).
Align your fasting schedule with your menstrual cycle. If you’re pre-menopausal, some times of the month will be better for fasting than others. (More on that in the next section.) Fasting will cause fewer disruptions to your hormones if you match the timing up with your cycle.
Align your fasting schedule with your circadian rhythms. Circadian rhythms regulate the sleep-wake cycle and tell your body when to produce and release certain hormones. Intermittent fasting influences these circadian rhythms, so make sure you align your fasting schedule with your body’s natural sleep-wake cycle—which may be different from someone else’s schedule. Find the ideal fasting schedule for your circadian rhythm here.
Eat healthy, nutritious foods. Intermittent fasting is all about when you eat, but what you eat still matters. Filling your eating hours—especially your first meal of the day—with nutritious foods will support normal hormone balances and help you get the most from intermittent fasting.
Don’t skimp on protein. This is especially important for women over 50. Protein plays a crucial role in preserving muscle mass, so make sure you’re getting plenty of it during your eating window.
Important note: if you are pregnant, nursing, or trying to conceive, consult with your doctor before making major dietary changes. Also, if you have less than 20% body fat, it is extra important to maintain a healthy, balanced diet during your eating window to ensure you have the nutrition you need to support normal, healthy hormone levels.
Best intermittent schedules for women
Generally, fasting for 12 hours a day (12:12), 14 hours a day (14:10), and 16 hours a day (16:8) are the best fasting lengths for women. Your age, cycle, and lifestyle will help you pin down which fasting window is best for you, but here are some good guidelines to follow.
20s and 30s
These are the years it is most important to synch up your fasting times with your cycle. During the follicular phase (days 1-14), most women find that they can tolerate longer fasting windows (14-16 hours). During the luteal phase (days 15-28), progesterone levels increase, so a more moderate approach to fasting (12-14 hours) might be more appropriate.
40s
As women approach perimenopause, hormone fluctuations can intensify. Estrogen levels drop, and the body becomes more sensitive to insulin. A shorter fasting window (12-14 hours) may work best to help keeping energy and hormone levels stable.
50s and beyond
Post-menopausal women often experience a more stable hormonal environment, giving them more freedom to adjust their fasting schedule as they see fit. A longer fast (16 hours) is more doable during these years, and can be a good way to help keep blood sugar levels and weight management in check.
Making intermittent fasting work for you
Many have found success with intermittent fasting, but there isn’t a one-size-fits-all way of doing it. Women can find what works best for them by listening to their bodies and choosing fasting schedules that align with their unique biological rhythms. When done thoughtfully, intermittent fasting can be an empowering tool for improved health and overall well-being. Visit the Unicity blog for more intermittent fasting tips.
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