Why ‘yo-yo dieting’ may not be as harmful as often believed

Many people experience fluctuations in body weight throughout their lives, and so‑called yo‑yo dieting has long been considered a health risk – in some cases even more harmful than remaining overweight.

It has, for example, been associated with negative health effects such as increased fat mass, loss of muscle mass, reduced metabolic rate and a higher risk of diseases including type 2 diabetes and cardiovascular disease.

However, careful evaluation of the research does not provide strong evidence that these negative effects can be attributed to yo‑yo dieting in itself – or that it is more harmful than persistent overweight, says Professor Faidon Magkos from the Department of Nutrition, Exercise and Sports at the University of Copenhagen, who together with a German colleague has reviewed the available research in a comprehensive analysis.

“Many people refrain from trying to lose weight because they fear that subsequent weight regain may harm the body or their metabolism. Our review indicates that these concerns are largely unfounded. In most cases, the benefits of weight loss outweigh the potential risks of later weight regain,” says Faidon Magkos.

What the analysis shows

In their analysis, the researchers reviewed a wide range of selected studies, including observational studies, clinical trials and animal studies, which examine the effects of repeated weight loss and weight regain on, among other things, body weight, body composition and metabolism.

A key finding is that associations between yo‑yo dieting and poor health are often not supported as causal relationships. Many studies are based on self‑reported weight, which makes it difficult to determine cause and effect. In addition, it is often unclear whether weight loss is due to deliberate attempts or underlying illness.

“When you take into account existing disease, ageing and overall exposure to obesity, the supposed harmful effects of yo‑yo dieting largely disappear,” explains Professor Norbert Stefan from the German Center for Diabetes Research (DZD), University Hospital Tübingen and Helmholtz Munich.

Weight regain is not the same as harm

For individuals whose weight fluctuates, the researchers emphasise that many of the health benefits of weight loss are lost when weight is regained.

However, this does not mean that individuals are worse off than before the weight loss, says Faidon Magkos:

“When the weight returns, you move back towards a level of risk similar to before — not beyond it. There is a crucial difference between losing benefits and causing harm.”

According to the researchers, several large studies show that the degree of obesity itself — rather than weight fluctuations — appears to be the primary driver of the risk of metabolic disease.

Implications for weight loss and treatment

In recent years, weight‑loss medication has become increasingly widespread, and such treatments can lead to substantial weight loss that is often followed by significant weight regain if the medication is discontinued.

According to the authors, this pattern should not necessarily be interpreted as harmful. On the contrary, intermittent weight loss — even if not maintained permanently — can provide meaningful periods of improved metabolic health and quality of life.

The researchers also highlight that most individuals who ultimately achieve long‑term weight loss have experienced multiple unsuccessful attempts along the way. Weight loss followed by weight regain is therefore often a necessary step on the path to success — rather than a sign of failure or a health risk.

For that reason, the two researchers emphasize an important message for patients and clinicians:

“People with overweight should not be discouraged from attempting to lose weight, even if they find it difficult to maintain in the long term. Unsuccessful weight‑loss attempts are not harmful, but giving up altogether may be,” they say.

[[ Facts: About the format

• The scientific article is a Personal View, a format in which existing knowledge in the field is synthesised into an expert, evidence‑based assessment.
• A Personal View is peer‑reviewed.
• There may be disagreement among researchers regarding the analysis.
• The analysis has been published in the international peer‑reviewed medical journal The Lancet Diabetes and Endocrinology.
• Read more about The Lancet and the Personal View format.

Facts: What the analysis shows

The researchers challenge the interpretation that yo‑yo dieting is harmful in itself.
They do not find strong evidence that repeated weight loss and weight regain leads to lasting health damage.

They point out that these concerns have shaped both public communication and clinical advice, contributing to a widespread perception that repeated weight‑loss attempts may do more harm than good.

Associations between yo‑yo dieting and disease are often not causal, but may instead reflect other underlying factors, according to the analysis.

Concern about regaining weight after weight loss should not discourage individuals from attempting to lose weight. ]]