The research suggests that yo-yo dieting is harmful in several respects: fat cells develop a biological memory that causes weight to return more quickly, resting metabolism declines, and there are associations with psychological complaints and a higher risk of death from cardiovascular disease. The evidence rests on animal research and observational studies in humans, so there is not yet conclusive clinical proof. Practically speaking, a sustainable, gradual approach is better than repeatedly strict dieting followed by relapse, although not losing weight when overweight is also not a good alternative.
Fat cells have a kind of biological memory. Research in mice, confirmed in human fat tissue, shows that after weight loss, fat cells retain stable chemical changes that make them more prone to an unhealthy response when you eat fat again. Mice with this so-called 'obesity memory' regained weight faster after resuming a high-fat diet than mice without that history1. Whether and how strongly this effect occurs in humans has not yet been precisely quantified.
Dieting also lowers your resting metabolism, meaning the amount of energy your body burns at rest. This makes it easier to regain weight after stopping a diet2. Both mechanisms together, the biological memory in fat cells and a slower metabolism, may explain why each successive yo-yo cycle sometimes feels harder.
Older studies found no consistent evidence that previous weight-loss attempts make later attempts structurally harder, or that muscle mass is lost disproportionately with repeated yo-yo dieting3,4. The ratio of fat mass to muscle mass does not change meaningfully differently through yo-yo dieting compared with a single episode of weight loss. This is a commonly heard concern that is not supported by current research.
What has been demonstrated epidemiologically are associations between large weight fluctuations and an increased risk of death from cardiovascular disease and from all causes combined3. An important caveat: these are associations. It has not been proven that the fluctuations themselves are the cause; people with greater weight fluctuations may already be more vulnerable for other reasons.
Yo-yo dieting also has a psychological dimension. Repeatedly gaining and losing weight is associated with a higher likelihood of binge eating, dissatisfaction with life, and lower self-confidence about appearance3,5. This association has been shown to be statistically significant, though that says nothing yet about the direction of causality.
Finally, a nuanced point about the liver. In mouse research, repeated weight cycling turned out to be better for the liver than not losing weight at all: inflammation decreased markedly compared with continuous unhealthy eating6. There was a slight increase in a specific form of fat accumulation in the liver. This has only been studied in animals and says nothing about long-term consequences in humans, but it shows that yo-yo dieting is not in every respect more harmful than remaining overweight.
The claims are based on a combination of mouse studies, epidemiological observational research, and partly human tissue research. No large randomised trials are available on the long-term consequences of yo-yo dieting in humans. The epigenetic findings (PMID 39558077) have been partly confirmed in human fat tissue but not in an intervention study. Mortality figures (PMID 8002684) are associative.