Intermittent Fasting Is All the Rage, But Does It Work?

By Andrea Atkins
Reviewed by Daniel Lew, M.D.
July 03, 2023

Three years ago, Jessica Hernandez was constantly thinking about food.

“I was so in my head about eating, I was going crazy,” says Hernandez, 50, of East Greenwich, Rhode Island. “I was saying, ‘I want to lose 3 pounds.’ And even though I was eating a low-fat diet, my weight seemed to be going up no matter what I did.”

After breakfast at 9 a.m., a snack at 10:30 a.m., lunch at noon, and a midafternoon snack, Hernandez ate dinner, then struggled over whether to have dessert. When she discovered Delay, Don’t Deny: Living an Intermittent Fasting Lifestyle by Gin Stephens, she was intrigued.

“It seemed like it was speaking to me. ‘You’ve tried all these diets, you’re in midlife facing menopause, and nothing’s working.’ That was me,” recalls Hernandez.

What Is Intermittent Fasting, Exactly?

Like millions of women, Hernandez discovered intermittent fasting (IF)—an eating plan that alternates periods of eating with periods of fasting. The idea behind IF is that it creates a caloric deficit ultimately leading to lower caloric consumption over the course of a week. It may also affect the hormones that influence metabolism and, over time, change the appetite-regulating hormones causing less hunger overall. It especially appeals to women in midlife, many of whom have tried other approaches to weight maintenance and, by their 40s, are looking for something new.

There are several ways to approach intermittent fasting, but the most common are:

  • The 16:8 method: Fast for 16 hours each day and eat only during a recurring eight-hour window.
  • The 5:2 method: Eat only 500 to 600 calories total for two days each week and eat normally the other five days.
  • Alternate-Day Fasting: Restrict your calories to 500 on alternate days and eat regularly on the other days.

Intermittent Fasting in Midlife Women

Hernandez was specifically intrigued because, as she says, “What I was reading seemed to say that hormones were regulating my weight more so than simply ‘Calories in, calories out.’”

Melissa Schuster, R.D.N., an integrative dietitian and owner/founder of Schuster Nutrition in New York City says IF can help with weight loss. But those who swear by IF are using it for more than weight loss.

“Why would I go back to eating breakfast?” Hernandez asks. “Whatever breakfast I’m missing, I’ll just eat for lunch. This isn’t a diet, it’s a way of life.”

Some women say the IF brings them more energy and they just feel better in general, something Schuster says she understands. “Hormones follow the sun,” Schuster explains. “Our body is not equipped to eat late at night. We often hold onto those calories. Fasting in that way is a good tool to ensure that you eat only during the waking hours, which will also benefit digestion.” A small 2020 study involving 45 women over 60 showed that the women who completed six weeks of IF, fasting for 16 hours a day, lost about 4 pounds.

There are no studies that have looked at whether this eating plan is superior for women in menopause or perimenopause, says Krista A. Varady, Ph.D., a professor of kinesiology and nutrition at the University of Illinois Chicago. But in a study comparing the alternate-day fasting results of premenopausal and post-menopausal women, Varady found that both groups achieved comparable results when it came to weight loss and body composition changes. Both groups also reduced key disease risk factors such as insulin, insulin resistance, and blood pressure. The post-menopausal women had a greater drop in LDL cholesterol (the bad kind), which suggests this kind of fast may help protect the heart.

Another benefit of intermittent fasting: There are no restricted foods, so if you want to eat apple pie during your eating window, you can eat a modest piece.

The Downsides to Intermittent Fasting

Despite the potential perks, not all experts love intermittent fasting.

“I don’t think that it’s better than any other diet,” says Varady. “They all do the same thing—help people eat fewer calories.” Schuster agrees that IF is just another way to restrict food. IF is not for you if you overeat or binge during the nonfasting periods. Additionally, IF may interfere with social events, and it may be difficult for those who like to go out a lot to follow an IF regimen.

“The first ten days are really tough for everyone,” Varady says. “It just takes your body a while to adjust to these hours of hunger. People experience mild constipation, irritability, headaches, but no major safety issues.” IF is not for everyone. You can feel very tired because of less calories and energy. Your sleep patterns can be disrupted. You feel hungry all the time.

While most studies have generally shown positive results in terms of weight loss, some worry that intermittent fasting has yet to be studied extensively enough in humans to really know the long-term effects. A 2020 study published in JAMA Internal Medicine found that intermittent fasting is no better at helping obese patients lose weight than eating healthily and steadily throughout the day. Additionally, intermittent fasting may also have an effect on women's menstrual cycles. An article from the journal Thyroid shows that fasting for long periods can affect the hypothalamus. Although this study was conducted in rats and mice, the results may suggest that IF may affect the hypothalamus in humans, which can affect estrogen and progesterone levels and can change menstruation patterns as a result.

IF may also be more effective for men than for women. A slightly older small study (involving only eight men and eight women) found that men who fasted improved in terms of insulin sensitivity, while women who fasted did not. Plus, the women’s glucose tolerance declined due to the fasting. Researchers determined that IF may be less effective in women for weight loss and blood-sugar management than in men.

For those who have ever had an eating disorder, IF is not recommended. In fact, the Center for Discovery Eating Disorder Treatment center specifically calls it out as dangerous for anyone who has ever had disordered eating in the past, as it can be triggering.

Proceed with Caution

Always talk to your doctor before starting any diet plan. Start slowly, with shorter fasting periods in the beginning; then, gradually increase the fasting periods. Watch out for signs that you are over-restricting your calories, including light-headedness, dizziness, and irritability. While Varady says intermittent fasting is considered safe for most people, there are some people who should absolutely avoid it. They are:

  • The elderly, because it may reduce muscle mass
  • Pregnant or lactating women, who need many calories
  • Children, who need calories to grow
  • Teenagers, who may be vulnerable to eating disorders
  • People with diabetes (should consult with a doctor)
  • People with eating disorders

More research is definitely needed before anyone can declare IF some kind of wonder diet.

Advantages Over Other Diets

For Caitlin Kelly, a writer over 50 from Tarrytown, New York, the 16:8 plan, which she began in November, 2020, doesn’t feel restrictive. There is no app or food journal, and she doesn’t count calories. She doesn’t even own a scale, but when she went for her annual physical in January, 2021, she’d lost 10 pounds.

“I felt like I could cry,” Kelly says. “I’d only lost 10 pounds, but it was the first time in 20 years that the scale had gone down.”

While it is true that you can technically eat whatever you want when you are not fasting, to achieve maximum benefits, it is more beneficial to consume healthier foods when you are eating. Both Hernandez and Kelly agree that they are mindful of what they eat during their window—lots of fresh fruits and vegetables, legumes, omelets, lean proteins. They both avoid processed food and, on most days, skip dessert. “But if I want them, I’ll eat two cookies,” says Kelly.

Hernandez says she too indulges regularly, but now, “After an indulgent day, I just feel so full. I don’t want to eat so much the next day,” she says.

Still, being mindful of nutrition is always a key component of any diet and IF is no different, says Schuster, who is concerned it may not be a sustainable long-term plan.

After three years, Hernandez would disagree. “I feel freer and more in control of my hunger,” she says. “No foods are off limits, and that has been one of the very liberating things for me. When I close the eating window, it’s a very strong motivator for me to not eat.”

Beyond weight loss, studies have shown that the benefits of IF go beyond weight loss and may include decreased risk for cardiovascular disease, delayed aging, and decreased inflammatory markers in your body.

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