Experts are warning that diets that aren’t “medically necessary” can “cause people real harm” and spur a “lifelong struggle” with their weight.

A new study, published in the journal Qualitative Health Research, found that yo-yo dieting or weight cycling can have long-lasting negative effects on dieters.

“Ultimately, this study tells us that weight cycling is a negative practice that can cause people real harm,” Lynsey Romo, an associate professor of communication at North Carolina State University and the study’s co-author, said in a statement.

“Our findings suggest that it can be damaging for people to begin dieting unless it is medically necessary. Dieting to meet some perceived societal standard inadvertently set participants up for years of shame, body dissatisfaction, unhappiness, stress, social comparisons, and weight-related preoccupation.”

Yo-yo dieting or weight cycling is when dieters become sucked into a cycle of dieting, regaining the weight they lost — or more — pushing them to diet again, usually with more extreme terms.

The issue “is a prevalent part of American culture, with fad diets and lose-weight-quick plans or drugs normalized as people pursue beauty ideals,” Romo said.

The research team at North Carolina State University conducted in-depth interviews with 36 adults — 13 men and 23 women — who had experienced weight cycling.

“Overwhelmingly, participants did not start dieting for health reasons, but because they felt social pressure to lose weight,” Romo noted.

This social pressure pushed people to attempt to follow a long list of weight-loss diets and behaviors that were not medically advised.

Many of the participants admitted to disordered weight-management behaviors, such as binge or emotional eating, restricting food and calories, memorizing calorie counts, stressing about what they were eating and how much they weighed.

Most of them resorted to falling back on quick fixes (such as low-carb diets or diet drugs), overexercising and avoiding social events with food.

Although the participants used a wide variety of weight-loss strategies, most regained all if not more of the pounds they initially shed as these diets and behaviors became “unsustainable.”

To add to that, people then felt ashamed when they regained the weight back and eventually felt worse about themselves than they did before they began dieting. 

This then pushed them to attempt increasingly extreme behaviors to try to shed more pounds.

The few who were successful at breaking the yo-yo dieting cycle did so by adopting healthy eating behaviors — such as consuming a well-balanced diet and eating when hungry — rather than attempting to closely control their eating habits.

Also worrisome was that many “participants referred to the experience as an addiction or a vicious cycle.”

“Almost all of the study participants became obsessed with their weight,” Katelin Mueller, co-author of the study, said.

Losing weight became such an overwhelming part of these people’s lives that they became distracted or dissuaded from spending time with friends and family to reduce the temptation of breaking their diets.

“The combination of ingrained thought patterns, societal expectations, toxic diet culture, and pervasive weight stigma make it difficult for people to completely exit the cycle, even when they really want to,” Romo said.

“Once a diet has begun, it is very difficult for many people to avoid a lifelong struggle with their weight.”