What Really Happens When You Yo-Yo Diet

Yo-Yo Dieting: What Really Happens to Your Body
Photo: Michal Kulesza

It’s so tempting: You’ve got something big coming up on the calendar that you want to look your best for. Why not diet hard and exercise a ton to get some weight off? Inevitably, though, even if you succeed, studies show you’ll gain it all back as soon as you go back to your normal eating habits. But what’s all this yo-yo dieting really doing to your body — and psyche?

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What Is Yo-Yo Dieting Anyway?

First, let’s talk about the two types of yo-yo dieting. One happens when you’ve lost weight in the past through smart, healthy eating and moderate exercise and then something knocked you off the wellness path and you gained it right back. (Annnd… repeat cycle.)

There is nothing wrong with this, says Tiffany Wright, PhD, founder of Skinny Coach Solution. “Every minute that you’re at a healthy weight is beneficial for you. It’s less stress on your heart and arteries, reduces your risk of disease, and increases your lifespan tremendously,” she says. In fact, one study published in the American Journal of Epidemiology found that there was no increased risk of cancer in people who “weight cycled” (the official term for yo-yo’ing).

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Other research on widely held weight loss myths disproved the commonly held belief that yo-yo’ing boosts odds of mortality. There just isn’t enough evidence to say that’s the case. The ultimate takeaway, say researchers: Don’t stop trying to lose the weight.

When Yo-Yo’ing Is a No-No

In the second type of yo-yo scenario, you’ve made the decision to crash diet and live off of kale and almonds, stick to 1,000 calories a day, or try one of those weird juice detoxes. Inevitably, that’s not sustainable. When you go back to eating again, you regain the weight — and then some. Here’s what’s happening to your body:

Your metabolism: “When you drop your calories, your metabolism will slow down,” says Charlie Seltzer, MD, a medical weight loss expert in Philadelphia. Then, you go back to eating normally, but this time with a slower metabolism, which will cause you to gain fat. Fear not, the metabolic slow-down is not permanent, but by the time those calorie-torching engines return to normal, you may be 10 or 15 pounds heavier than before, he explains. Worse yet, you may be tempted to try another crash diet, lose the weight, regain it (and more again). That’s one reason dieting can make people gain even more weight.

Your muscles: Severely restrict calories and you’ll lose fat — and muscle. The latter is not such a good thing. “When you eat normally again, you’ll regain more of this weight as fat. So your body composition can actually get worse,” says Dr. Seltzer. The fix here is moderately cutting calories while continuing to exercise. That way you’ll maintain muscle mass while trimming fat.

“When [your body is] stressed out, the increase in cortisol (the stress hormone) will prompt your body store fat and prevent weight loss.”

Weight loss: Simply being hungry and not getting the nutrients necessary to function properly sends a 9-1-1 call to your body — that’s stressful in itself. And when it’s stressed out, the increase in cortisol (the stress hormone) will prompt your body store fat and prevent weight loss, explains Wright.

Your heart: If you’re regaining mostly fat, that’s a drag on your ticker. It may be one reason why yo-yo weight loss has been shown to affect factors like cholesterol and triglyceride numbers, which can increase heart disease risk. Diet severely enough, and this can mess with your hydration and electrolyte balance, something that can be fatal, adds Wright.

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Your psyche: Restricting calories mucks up the hormones your thyroid releases. Problem is, says Dr. Seltzer, this also ups cortisol production, which has the unhappy effect of fueling a raging appetite. (Can you see why excess cortisol is often no good?) “The first thing you’ll do when you’re stressed, tired, or sad is overeat,” he says.

How to Break the Cycle

If you struggle with yo-yo weight loss, it’s a good tip off that what you’ve done in the past hasn’t worked, so you need a different approach, says Dr. Seltzer. “I try to get patients away from solely thinking about the scale and instead focusing on health factors, like how much can you deadlift? Are you sleeping better?” (Check out these awesome non-scale victories as inspiration.) And, it’s also about identifying and addressing underlying issues with food, like emotional eating. “Without that, the likelihood of long-term success is almost zero,” he says.

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