- Two new studies point to some downfalls of intermittent fasting (IF), a method of eating in which you restrict the hours (or days) that you consume calories.
- One study, published in Eating Disorders, suggests IF could lead to disordered eating, especially in young people.
- Another study, published in Obesity, found that levels of dehydroepiandrosterone (DHEA), a reproductive hormone, was significantly lower after eight weeks of IF.
Also called time-restricted eating, intermittent fasting (IF) involves eating all your calories for the day within a certain timeframe, such as an eight-hour window. You can also follow an intermittent fasting method in which you fast for whole days—for example, a technique called 5:2 means fasting for two non-consecutive days per week and eating normally the other five days.
Either way, previous research shows benefits to intermittent fasting, including some improvement in blood pressure and blood sugar regulation. A study in the International Journal of Endocrinology noted that the strategy seems so effective for those with metabolic syndrome, helping to improve insulin resistance, that it should be considered as part of treatment.
But not all research on IF is about advantages. A recent study published in Eating Disorders suggests the approach could prompt disordered eating, especially in young people. Looking at more than 2,700 adolescents and young adults, researchers found a link between intermittent fasting and behaviors like binge eating, vomiting, and compulsive exercise.
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Among the study participants, the prevalence of IF was notable, according to lead author Kyle Ganson, Ph.D., assistant professor at the University of Toronto’s Factor-Inwentash Faculty of Social Work. He told Runner’s World that 47 percent of women, 38 percent of men, and 52 percent of transgender or gender non-conforming individuals reported engaging in IF within the past year.
“We found that engagement in any intermittent fasting over the past 12 months, which is defined as abstaining for food for at least eight hours, was associated with eating disorder behaviors,” he said. “This was in line with what we expected, but we were surprised at how common IF was among participants. Also, we found each group fasted, on average, more than 100 days in the past year. That was concerning, given the association with dangerous behaviors.”
In terms of why prevalence was higher among transgender and gender non-conforming participants, Ganson said this is likely due to the stress of living daily with marginalization, oppression, and discrimination from society.
“Eating disorder behaviors for this group can be a means of control and emotion regulation,” he said. “Additionally, these individuals may use eating disorder behaviors to alter their bodies to adhere to sociocultural body ideals of their identified gender.”
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This wasn’t the only recent study to find some downsides to intermittent fasting. Research published in Obesity looked at an eight-week IF program for 12 premenopausal women and 11 postmenopausal women with obesity. Participants ate for only four or six hours per day. They found that while some hormone levels remained the same, levels of a certain reproductive hormone called dehydroepiandrosterone (DHEA) was significantly lower after those eight weeks.
DHEA is typically produced in the adrenal cortex and ovaries, and according to other research, it can improve ovarian function and increase chances of getting pregnant. While researchers said this reduction in DHEA could actually benefit premenopausal women with obesity, as it could lower breast cancer risk, they also point out a drop in DHEA may be a concern for postmenopausal women. That’s because they’re already dealing with lower estrogen levels and DHEA is a primary component of that hormone. Lower DHEA in this population could result in sexual dysfunction, diminished skin tone, and vaginal dryness. (These side effects weren’t noted in the study participants, however.)
Keep in mind that studies like these two don’t necessarily mean intermittent fasting should never be an option. We still need more research on the effects of IF on female sex hormones, for example, as the Obesity study was small. But it is important to pay attention to how the strategy might be affecting you, says Jason Fung, M.D., author of The Complete Guide to Fasting. For example, fasting shouldn’t involve a dramatic drop in calories, he told Runner’s World. He also said no one should ignore side effects related to physical discomfort or problematic behaviors related to eating.
Often, the best strategy to determining if intermittent fasting is right for you is to do a short stint of fasting and have a more generous eating window to reduce feelings of restriction. This can help you pay attention to how IF is working for you. It can also help you pay attention to your food choices, which in itself can be a major benefit, Fung suggested.
“Just giving fasting a try usually results in greater awareness about what you’re eating, not just when you eat,” said Fung. “So even if it doesn’t work for you, it’s likely you've benefitted from making a shift toward eating healthier foods, for example.”
The bottom line on intermittent fasting is that it’s for some people, but not others. If you’re concerned about the potential downsides to it—for example, if you’ve had disordered eating in the past, you’re trying to get pregnant, or you’re just unsure how it will affect your body—be sure to talk with your doctor about whether the strategy is right for you and how to use it in a way that supports your health.
Elizabeth Millard is a freelance writer focusing on health, wellness, fitness, and food.
