What to Know About Intermittent Fasting for Women

Fasting for women vs. men

From weight loss to longevity, intermittent fasting comes with a long list of potential benefits. Now, a small but growing body of evidence suggests that these fasts may offer a different set of advantages and drawbacks for women than men.

Intermittent fasting is a blanket term for several different eating plans that alternate between periods of eating and fasting. These diets focus more on when you eat and less on what you eat.

Time-restricted feeding, for example, limits eating to a certain window of time each day. The popular 16:8 method lets you eat for eight hours and then fast for 16. You might, for example, eat only between 7 a.m. and 3 p.m., or between 11:30 a.m. and 7:30 p.m. In contrast, alternate day fasting is a pattern of feasting one day and fasting the next.

The benefits of intermittent fasting vary based on the type of fast, its duration, and maybe even your gender.

“We don’t know a lot about how the experience with intermittent varies by men versus women yet,” says Courtney M. Peterson, PhD, associate professor in the department of nutrition sciences at the University of Alabama, in Birmingham. Researchers are working on unraveling some of these differences and have made some key inroads, she says.

Women may react faster

Specifically, women may feel the effects of fasting sooner than men. A metabolic switch is flipped on during fasting. When this happens, you start to burn fat instead of glucose (or blood sugar) for energy. This accounts for some of the benefits associated with some fasting methods.

Women may hit the switch sooner than men when following an intermittent fasting regimen, according to Peterson. “We see more fat in their bloodstream compared with men who fasted for similar amounts of time,” she says.

This suggests that women could see results with shorter fasting windows. Women may have success following a 16:8 plan versus an 18:6 plan, which requires fasting for 18 hours and eat during a six-hour window. “Studies in animals are being done to see if females might benefit from slightly shorter fasting durations than males,” Peterson says.

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Weight loss

Which type of intermittent fast is best in terms of weight loss? It’s likely the one that you can stick with long-term and fits in with your lifestyle.

Research suggests, however, that fasting weight loss success in women may also be tied to stricter diets. Most intermittent fasts don’t limit what you can have during eating windows or days. But a study, published in 2019 in Obesity, found that obese women lost more weight by fasting intermittently when they also followed a strict diet. The study included three additional groups for comparison: Women who fasted intermittently but didn’t cut back on food, women who reduced their food intake but didn’t fast, and a group of women who didn’t restrict their diet in any way at all. (Don’t forget, your diet includes what you drink. Here’s what you’re allowed to drink while intermittent fasting.)

When researchers followed these 88 women over 10 weeks, they found that obese women who ate 30 percent fewer calories than they would normally need and fasted intermittently, they lost more weight than the other groups—slightly more than two pounds a week.

Insulin resistance

Weight gain or a poor diet can trigger lead to your muscles and cells to resist the efforts of the hormone insulin to supply blood sugar for energy. As a result, more sugar remains in the bloodstream where it can raise the risk of chronic conditions such as type 2 diabetes. When following an intermittent fasting regimen, people often see improvements in insulin resistance. But women may see less of an effect than men, Peterson says. Researchers don’t fully understand why this happens, and more studies are needed to confirm these observations, she says.

Insulin resistance occurs when your body doesn’t respond well to insulin and can’t easily use glucose for energy. As a result, your pancreas makes more insulin and your blood sugar levels can go up. Insulin resistance is a sign of prediabetes.

Intermittent fasting and fertility

Does fasting affect fertility and menstrual cycles? At least one study found that fasting doesn’t affect hormone levels in premenopausal women. However, studies of Muslim women who fast from dawn to dusk for 30 days during Ramadan suggest there could be some menstrual irregularities associated with fasting. Those include heavier-than-usual flow, and infrequent or overly frequent periods—especially during fasts of more than 15 days. Irregular menstrual periods can affect a woman’s chances of becoming pregnant, but this wasn’t analyzed in the study.

Post-menopause benefits

For women, age may also play a role in how the body responds to intermittent fasting, says Krista Varady, PhD, professor of nutrition at the University of Illinois in Chicago, and author of The Every-Other-Day Diet. Postmenopausal women may lose twice as much weight as younger, premenopausal women when fasting, she says. After 12 months of following an alternate day fasting schedule, postmenopausal women lost more than 24 pounds, she says, citing some early results from her lab that is still under review. “Likewise, after three months of time-restricted fasting (also known as 16:8), post-menopausal women lost nine pounds,” she says.

Belly fat

Research from 2014 published in the journal Translational Research suggests that both alternate day fasting and time-restricted fasting reduces belly fat, This is important as belly fat in postmenopausal women is associated with a higher risk for heart attack and stroke than in men. This fat may release inflammatory chemicals and other molecules that can increase the risk of heart disease, liver disease, diabetes, and other health conditions.

Heart risk

Older women may see additional heart benefits. When following intermittent fasting, postmenopausal women showed a 20 percent decrease in “bad” or low-density lipoprotein (LDL) cholesterol, reductions in blood pressure, and 20 to 40 percent decreases in insulin resistance. High levels of LDL cholesterol and high blood pressure can increase the risk of heart disease and stroke, and insulin resistance sets the stage for diabetes. “These improvements can help ward off heart disease and diabetes,” Varady says.

Bone health

Another benefit: bone health. Intermittent fasting doesn’t lead to bone loss in the way that regular dieting may, suggests a study published 2017 in Nutrition and Healthy Aging. During menopause, the dramatic decline in levels of the female sex hormone estrogen can affect bone strength, increasing risk for the brittle bone disease osteoporosis. This is important as 80 percent of the estimated 10 million Americans with osteoporosis, are women.

Cautions about intermittent fasting

Not every woman should try intermittent fasting. If you are pregnant or breastfeeding, intermittent fasting is not for you, says Robin Foroutan, RD, an integrative medicine dietitian at Morrison Center in New York City and spokesperson for the Academy of Nutrition and Dietetics. Fasting can restrict the amount of nutrients for mom and baby when they need it most, she says. It’s also not advisable for women (or men) with eating disorders, she says.

If you are considering intermittent fasting, work with a registered dietitian or health care provider to help you choose the best method for your goals, Foroutan says. Here’s what else to consider before trying intermittent fasting.

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