Repeatedly losing weight and then gaining it back may do more harm than simply making dieting frustrating.
A new study from the University of California, San Francisco (UCSF) suggests that this pattern, often called weight cycling or yo-yo dieting, may speed up the loss of muscle in middle-aged adults.
The findings are especially important now that modern weight-loss medicines are helping many more people lose weight.
Maintaining healthy muscle is important throughout life. Muscles help people move, stay balanced, protect joints, and keep up everyday activities.
As people grow older, they naturally lose muscle over time, and faster muscle loss can increase the risk of weakness, falls, disability, and poor health.
The researchers published their findings in the journal Radiology.
Although the study did not include people taking GLP-1 weight-loss medicines, the scientists said the results are highly relevant because many people may stop and restart these medicines, causing their weight to rise and fall.
The team analyzed health information and MRI scans from 1,433 middle-aged adults taking part in the long-running Osteoarthritis Initiative. This project follows people who either have knee osteoarthritis or are at higher risk of developing it.
Some participants kept a fairly stable weight during the four-year study, while others repeatedly lost and regained weight. The researchers used artificial intelligence to measure the amount of muscle in the thighs as well as fat inside the muscles and around the knee.
The differences between the two groups were clear. People whose weight changed repeatedly lost about 3.7% of their thigh muscle over four years. Those with relatively stable weight lost only about 1% of their thigh muscle during the same period.
Importantly, both groups finished the study at about the same overall body weight as when they started. This means the extra muscle loss was linked to repeated weight changes rather than ending up lighter overall.
The researchers adjusted their analysis for many other factors, including age, sex, body weight at the start of the study, physical activity, diet, and other health conditions. Even after these adjustments, repeated weight cycling remained strongly linked with greater muscle loss.
Lead researcher Dr. Thomas Link said that while people often regain body weight after dieting, they may not regain the muscle they lost. Instead, much of the weight regained may be body fat, leaving the body with less muscle than before.
The study does not prove that weight cycling directly causes muscle loss because it was observational. It also did not examine people using GLP-1 medicines. However, its large sample size, detailed MRI measurements, and four-year follow-up make the findings important.
Overall, the research suggests that successful weight management should focus not only on losing fat but also on protecting muscle. Regular resistance exercise, enough dietary protein, and medical guidance may become increasingly important as more people use modern weight-loss treatments. More research is needed to discover the best ways to preserve muscle during weight loss.
Review and analysis: This was a large, carefully conducted observational study using MRI scans, which provide accurate muscle measurements. Its findings are convincing but cannot prove cause and effect. Future clinical studies, especially involving GLP-1 medicines, will be needed to determine how muscle can best be protected while people lose weight.
If you care about wellness, please read studies about how ultra-processed foods and red meat influence your longevity, and why seafood may boost healthy aging.
For more health information, please see recent studies that olive oil may help you live longer, and vitamin D could help lower the risk of autoimmune diseases.
Source: University of California, San Francisco.
