Mind and Body

The thin line between intermittent fasting and eating disorders

The problem’s lynchpin is the difference between what scientists expect and what people actually do.

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As of August 2021, the subreddit for intermittent fasting has 786,000 members.

On it, people from around the world share tips, post progress pictures, ask questions, and give support. They endeavor to live a healthier life through refraining, on a schedule, from eating.

Prominently displayed on the right corner of the webpage are the rules for the forum. The third reads: “No pro-ED rhetoric.”

ED is shorthand for “eating disorder.” It’s perhaps the biggest elephant in the room when it comes to conversations about one of the buzziest diet regimens to go mainstream.

And on its surface, it does look suspect: an eating practice that dictates extended periods where no food is allowed and others where you can eat anything you want verges uncomfortably close to the severe restriction or restrict-binge cycles that characterize anorexia and bulimia.

Scientists who investigate intermittent fasting, however, tell Inverse the potential health benefits outweigh the risks. Mental health specialists, meanwhile, tell a slightly different story: there’s no safe way to do it, and the practice plays into harmful ideas about food that especially appeal to men.

The problem’s lynchpin is, seemingly, the difference between people doing what’s recommended — the sort of eating patterns studied by scientists — and where people decide to push the limits. Passionate adherents argue it’s done wonders, influencing factors of health ranging from diabetes to lowering blood pressure. Some even say it’s positively changed their relationship with food.

But a line can be crossed — often without one realizing it.

Is fasting a form of eating disorder?

The “no pro-ED” rule on the Reddit group specifies that: “Any posts and comments featuring diets, routines, and advice that falls consistently below the medically recommended minimums will be removed.”

“People should stay away from the idea of just eating once a day.”

Yet in forums like these — r/fasting on Reddit, Facebook groups like Intermittent Fasting Lifestyle, and across Instagram pages — posts about 36-hour fasts, 20-hour fasting windows in a 24-hour day, and OMAD (or “one meal a day”) abound. Intermittent fasting researchers themselves don’t recommend measures as extreme as these.

“People should stay away from the idea of just eating once a day,” Valter Longo tells Inverse. Longo is a professor at the University of Southern California and the director of the Longevity and Cancer Program at the IFOM Institute of Molecular Oncology.

This is “very, very risky,” he says. “In fact, based on the data, it is problematic.” In this case, the problem Longo refers to isn’t developing an eating disorder. Instead, it’s putting oneself at risk for cardiovascular disease, gall-bladder issues, and cancer.

But a 12 or 13-hour fasting window, Longo says, “is very, very safe.”

Posts on r/intermittentfasting.


“Everybody can do it,” he says. “Not only can everybody do it, but people have been doing it, certainly, for hundreds of years.” This modest regimen might not even be a change for most, or how some define intermittent fasting.

Courtney Peterson has a slightly different perspective. Peterson is an associate professor of nutrition at the University of Alabama. She studies time-restricted eating, the least restrictive and most flexible forms of intermittent fasting.

“Our best data suggests that if you don't currently have an eating problem, then intermittent fasting doesn't lead to eating disorders or problems in that regard,” Peterson tells Inverse.

Still, Peterson does say this data refers to the very few human studies that have looked at a connection between intermittent fasting and eating disorders. She estimates there are two: One examined people with obesity who tried alternate-day fasting and found that there were no increased symptoms of eating disorders. In fact, body image improved.

The other looked at college students who self-identified as practicing intermittent fasting, on a 16:8 schedule, and found that more than 30 percent scored above the clinical cutoff for eating disorders — significantly higher than “community norms.” The authors concluded: “Results suggest that IF [intermittent fasting] is associated with ED [eating disorder] symptomatology.”

When intermittent fasting can go too far

“Intermittent fasting came on the scene about five to six years ago,” Brian Pollack tells Inverse.

He’s the clinical director of Hilltop Behavioral Health, a center that, among other things, specializes in eating disorder treatment for men. He’s worked with clients with eating disorders for over a decade.

“It's starting to be an acceptable way to eat by many, many young men. And the problem, of course, is that's why we're seeing it more and more in our clinical offices,” he says.

“It's starting to be an acceptable way to eat by many, many young men.”

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This is especially true concerning male clients between 14 and 19. “I would say it comes up 80 percent of the time,” Pollack says.

Pollack works with a group of clients, half of whom are male. Eating disorders in men, he explains, present in a very specific way.

“Often it culminates around the intensity of a cut, physically fit body, which allows them to often not feel weak,” he says. “They won’t feel weak, so they won’t feel vulnerable.” He thinks this effort underlies why so many men try to control their bodies through actions like intermittent fasting or ketosis.

“It really is somewhat of a gateway drug to concerns about body and food.”

Intermittent fasting, he says, is also less geared toward women than other diet plans. Although some men do, most don’t relate to feminized weight loss products and programs, like Weight Watchers and Jenny Craig, he explains. Instead, many men search for a way that empowers them to both “sculpt their bodies and their lives.”

But this mashup of regimented eating and fitness can come with a heavy cost, he says. The “metabolic switch” that’s at the cornerstone of many approaches to fasting and ketogenic diets “doesn’t work,” Pollack says. “It leads to more disordered eating, more body dysmorphic concerns; more intense anxiety and obsessions.”

Furthermore, the kinds of foods his clients eat as a part of their intermittent fasting regimen, he says, aren’t always nutritionally sound. This can, he claims, cause“higher anxiety, deeper bouts of depression, dissatisfaction.”

“It really is somewhat of a gateway drug to concerns about body and food.”

Different intermittent fasting methods

Intermittent fasting describes an eating regimen that falls loosely into one of a few categories, Peterson explains:

  • Time-restricted eating, where windows of time are defined for fasting and eating over 24 hours. A common ratio of fasting to eating is 16:8, but wider or narrower windows can be set.
  • Extended fasting, where one embarks on a 24-hour or more period without food, while continuing to hydrate.
  • Alternate day fasting, where food is eliminated or significantly restricted every other day.
  • A “fasting-mimicking” diet, where food is significantly restricted for a set period of time, like in the meal kits Valter Longo sells, or the “warrior diet”, where 2 days out of every week allow very restricted calories.

From limited human trials and many animal studies, we can tentatively say that refraining from eating sporadically can impart some health benefits: some forms of fasting have been shown to reduce symptoms of diabetes, lower blood pressure, and reduce other metabolic markers. In clinical trials with humans, researchers have concluded that it can be a good alternative to simple calorie restriction plans.

But studies come with their limits. Because regular people use intermittent fasting in such different ways, it can be difficult to know what mechanisms are driving the effects people experience — and, in turn, to point a finger of blame at the practice itself for fostering disordered eating.

One sticking point is whether or not calorie restriction itself is necessary for the “success” of intermittent fasting, an eating regimen that purports to let you eat as much as you want within the bounds of a schedule. It may have less to do when you eat, and more to do with how much.

This lack of distinction further blurs the lines between healthful discipline and problematic behavior.

For example, if you restrict the window of time you’re allowed to eat in enough, you’ll end up eating less overall. What’s more, intermittent fasting enthusiasts sharing their plans online often combine timed fasting with other dietary interventions like keto, or start exercising more.

The simple act of monitoring food may lead one to eat less.

So, is intermittent fasting a problem? — Pollack argues there’s no safe way to intermittently fast.

“All I can tell you is, no,” he says. “Unfortunately, we don't have any research that proves there are long-term results that are sustainable. And even in the short term, we're seeing people do undue damage to not only their physical health but their mental health.”

He acknowledges, however, that in his role as an eating disorder therapist, he only sees people who end up having problems — not those who say it’s turned their life around for the better. It’s easy to find dozens of online accounts where people say intermittent fasting has changed their relationship with food for the better.

Jason Leite of California shows what he eats as part of his intermittent fasting plan.

Michael Macor/The San Francisco Chronicle via Getty Images

According to Longo and Peterson, alongside evidence from limited human trials that use intermittent fasting as an intervention for metabolic problems, fasting can be a positive alternative to other diet interventions — as long as it isn’t taken to an extreme.

“I think there can absolutely be harm,” Peterson says. “I think what we'll probably end up finding, and this is just me guessing, is at the end of the day, it's probably safe for the majority of people who are adults.”

“But there's still going to be some people who it's not going to be appropriate,” she says. “And I don't know where that line should be yet.”

Peterson recommends an eight to 10-hour eating window and advises against any less. She says it’s hard to get a sense of warning signals for an eating disorder because “we're also working with people who need to lose some weight in the first place.”

Herein lies another issue, which Peterson does acknowledge: It’s a misconception that people who are deemed “overweight” don’t develop eating disorders. In fact, evidence suggests young adults with obesity are more likely to engage in disordered eating behaviors than those of “normal” weight — but are less likely to be diagnosed with a disorder.

This confusion is reinforced in medical guidelines: there just aren’t always clear boundaries between what is disordered eating and what isn’t.

“Disordered eating” is a term that isn’t yet defined diagnostically. You must meet very specific criteria to be diagnosed with a specific eating disorder like anorexia nervosa or bulimia nervosa, like meeting a certain BMI threshold.

“... if you start getting obsessive about that, I think a line needs to be drawn.”

But there’s a catchall for eating that meets some of the behavior Pollack has observed with patients who fast, known as “Other Specified Feeding and Eating Disorder.” According to the American Psychological Association, this category encompasses eating practices that cause distress and disrupt family, social, or work life.

Pollack places the threshold for problematic eating here, too.

“If it's causing dissatisfaction, and separation, from your happiness or sense of connection to your family or social life,” he says, “If it's taking control where you can’t eat at certain places, or go to certain places, or events, because you have to oblige by the rules, it’s a sign this might be becoming too rigid.”

Peterson says ultimately, dieticians and doctors must be diligent in asking their patients about histories of disordered eating and OCD.

While intermittent fasting does require a level of self-monitoring, “I’m not always a fan of the phrase ‘everything in moderation,’ because sometimes people use that to support things that are unhealthy,” Peterson says.

“But in this case, if you start getting obsessive about that, I think a line needs to be drawn,” she says.

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