What Really Happens to Your Body When You Yo-Yo Diet

At least a third of yo-yo dieters regain more weight than they lose, studies show. And, in one study, young women who weight-cycled were less likely than older dieters to maintain the weight loss long term.

With rapid weight loss, you lose lean tissue too, explains Jennifer Kuk, PhD, associate professor at the York University School of Kinesiology and Health Science in Toronto. But lean tissue returns much more slowly than fat when you yo-yo back.

“You [end up with] a little bit more fat and a little less lean tissue than you had before you lost weight,” she says.

Constantly losing and regaining weight can make people feel like they’ve failed, says Valerie Taylor, MD, PhD, head of psychiatry at Women’s College Hospital in Toronto.

She blames diets that tout how easy it is to take off the weight. They make you feel like a failure if they don’t work for you.

When a diet doesn’t stick, it can undermine your self-esteem and contribute to feelings of sadness, she observes. “If somebody already has depression, this kind of yo-yo dieting can make things worse.”

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The joy of reaching a dieting goal can quickly devolve into embarrassment when you cannot maintain the weight loss.

People go on “crazy diets” and lose weight “very quickly but inappropriately,” Dr. Taylor says. “Everybody tells them all kinds of great things about themselves,” she says. “And then they put the weight back on, and they just don’t want to go out and face people.”

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Your skin is like an elastic band. If you’re yo-yoing, say, 20 pounds with each weight cycle, eventually your skin goes slack, especially as you age, says Alan Matarasso, MD, clinical professor of surgery at the Hofstra/Northwell School of Medicine in Hempstead, New York.

“The expansion and contraction of the skin is what plays havoc,” explains Dr. Matarasso, who also serves as president-elect of the American Society of Plastic Surgeons.

He says damage can be widespread, showing up on the upper arms, abdomen, breasts, and back. Unfortunately, no amount of exercise will tighten the skin once it has stretched out.

RELATED: I Had 7 Lbs. of Skin Removed After Major Weight Loss—Here's What You Should Know

In a study of young and middle-aged women, weight cyclers were more likely to binge eat, and binge eaters gained more weight than their peers. Separately, an analysis of overweight and obese African American women revealed that weight cyclers were more likely to binge eat and have poorer body image than their non-cycling counterparts.

Michelle May, MD, founder and CEO of Am I Hungry?, which offers mindful eating programs and training, and author of Eat What You Love, Love What You Eat, says binge eating is a very common effect of food restriction. After a binge, people go back to dieting, “and that’s how that weight cycling starts.” When diets become impossible to sustain, “it reinforces the idea that somehow they have failed,” she says.

Older women are already at risk of bone loss due to a drop in estrogen during menopause. Yo-yo dieting may exacerbate the problem.

In one study, postmenopausal women who regained weight after losing it did not recover lost bone mineral density. The question is whether a small dip in bone mineral density affects long-term fracture risk.

At least in these older women, weight maintenance and fitness, rather than weight loss, “may be a more successful strategy for optimizing both bone and metabolic health,” the authors concluded.

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Rapidly losing and regaining weight may have serious consequences for people with heart disease.

A 2017 study found people with the greatest bodyweight fluctuations had twice the risk of heart attack, stroke, or death as those whose weight remained relatively stable–even after taking into consideration weight, smoking, and other cardiovascular risk factors.

The study doesn’t prove that yo-yo dieting causes worse health outcomes. But it does underscore the importance of maintaining weight loss. “It is absolutely worth it to lose weight if overweight or obese,” says the study’s lead author Sripal Bangalore, MD, director of complex coronary intervention at Bellevue Hospital in New York City. “However, it is best to lose weight and maintain the weight loss. As such, it may be more important to figure out strategies that would work in the long run.”

RELATED: Why Yo-Yo Dieting Is Seriously Bad for Your Heart (Even If You're Not Overweight)

Let’s be clear: Yo-yo dieting is not a recommended weight-loss strategy. But studies do show that even a small amount of weight loss–just 5% of your bodyweight–is beneficial when you’re obese.

That’s because fat stored in organs and muscle tissue is the first to go when you lose weight, explains Barbara Gower, PhD, professor of nutrition sciences at the University of Alabama at Birmingham School of Medicine.

That type of fat, especially deep in the belly, muscles, and liver, poses a greater risk of heart disease, diabetes, and stroke, especially in women, according to preliminary research presented at the 2017 Radiological Society of North America annual meeting.

Although it’s better to keep the weight off for good, “repeated bouts of weight loss are not necessarily bad,” Gower adds. Shedding that weight, even temporarily, “may reduce risk of chronic disease.”