The bad diet habit that can make you gain weight — even when you stop

Talk about a scale fail. 

New research suggests that a common dieting mistake may trigger lasting changes in the body that make eating right more difficult.

Worse still, the effects appear to linger long after the bad habit is corrected, quietly sabotaging your ability to maintain a healthy weight.

Yo-yo dieting is a pattern where people restrict calories to lose weight, then slip back into old eating habits — often gaining back more than they shed and starting the cycle all over again.

It’s a common problem in the US, where nearly three in four adults are clinically overweight and diet culture tends to favor quick weight-loss fixes over long-term lifestyle changes.

Studies estimate that up to 55% of American women and 35% of men have fallen into the yo-yo dieting trap at some point.

Curious how the cycle impacts the body, researchers in France put lab mice on a similar diet rollercoaster.

Over several weeks, the animals were fed alternating rounds of healthy, low-fat chow and a high-fat, high-sugar diet meant to imitate Western eating habits.

Just like in humans, their weight fluctuated up and down like a yo-yo. But over time, the mice also began binging on the junk food whenever it was available — even if they’d already been fed.

When researchers analyzed the mice’s fecal samples, they found long-lasting changes in their gut bacteria that altered their internal metabolism.

To test it further, the team transplanted the altered gut bacteria into healthy mice that hadn’t been dieting. They, too, started compulsively overeating fatty, sugary foods.

The researchers also scanned the mice’s brains and found increased activity in their reward centers, the region that lights up in response to pleasurable stimuli, including food.

The findings suggest that yo-yo dieting may mess with both the gut and the brain — making it tougher to resist high-calorie foods and setting the stage for overeating.

While the experiment hasn’t been tested in humans, the results suggest that yo-yo dieting could lead to similar changes in people as well.

The researchers said further studies will be needed to fully understand the biological mechanisms at play and confirm whether the same effect happens in humans.

Your gut and brain aren’t the only things yo-yo dieting can mess with.

“When weight is quickly lost and regained, the regained weight is typically fat tissue rather than muscle tissue, which can increase the overall body fat percentage over time,” Melissa Hoover, a registered dietician, said in an interview with Piedmont Healthcare.

One review found that 11 out of 19 studies linked a history of yo-yo dieting to higher body fat and more belly fat.

Hoover also noted that most yo-yo dieters focus on cutting calories but skip the exercise habits that help maintain muscle. “This eventually leads to loss of muscle mass and body strength,” she said.

And the risks don’t stop there. Yo-yo dieting has also been associated with an increased risk of developing chronic conditions like type 2 diabetes, heart disease and high blood pressure.

In fact, one study found that people who lose and regain weight on yo-yo diets are far more likely to die from heart attack or stroke than people who keep the scale on an even keel — even when that “steady” weight is slightly chubby.

Mentally, the cycle can wear people down. In studies, adults with a history of yo-yo dieting report feeling unhappy with both their health and overall quality of life.