For decades, yo-yo dieting has been treated like the dietary equivalent of repeatedly hitting yourself in the face with a frying pan - widely assumed to be worse than just staying heavy. But a major new review published in *The Lancet Diabetes & Endocrinology* suggests that this fear is about as scientifically grounded as the belief that eating after 8 p.m. turns all calories into pure regret.
Professors Faidon Magkos of the University of Copenhagen and Norbert Stefan of the German Center for Diabetes Research (DZD), University Hospital Tübingen, and Helmholtz Munich have spent a long time looking at a lot of studies involving both humans and animals, and they've come to a conclusion that will surprise exactly no one who's ever tried to lose weight: the evidence that weight cycling itself causes lasting harm is, to put it charitably, not very convincing.
"Many people struggling with weight are discouraged from trying to lose weight because they fear 'yo-yo dieting' will lead to muscle loss and somehow damage their metabolism," says Magkos. "Our review indicates that these fears are largely unsupported. In most cases, the benefits of trying to lose weight clearly outweigh the theoretical risks of weight cycling."
The researchers examined observational studies, randomized clinical trials, and animal studies, looking at how weight cycling affects body weight, body composition, metabolism, and blood sugar control. They found that once you account for pre-existing health conditions, aging, and overall obesity, the supposed harmful effects of weight cycling largely vanish.
"Regaining weight brings people back toward baseline risk - not beyond it," says Magkos. "There's a crucial difference between losing benefits and causing harm." In other words, you may not keep the weight off, but you won't end up in worse shape than if you'd never tried at all.
The review also has implications for the new generation of obesity drugs, including GLP-1 and dual incretin agonists, which can produce significant weight loss but often lead to regain after stopping. The researchers say this regain should not automatically be viewed as harmful, since even temporary weight reduction can still provide important health benefits and improve quality of life.
"The idea that 'yo-yo dieting ruins your metabolism' is not supported by robust evidence," Magkos and Stefan conclude. "Trying - and even failing - to lose weight is not harmful. But giving up altogether may be."