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Repeatedly losing and gaining weight may do more than frustrate dieters—it also accelerates muscle loss in middle-aged people, according to new UC San Francisco research that comes as weight-loss medications transform obesity treatment.
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In a study published in Radiology, researchers found that people whose weight repeatedly fluctuated lost significantly more thigh muscle over four years than people whose weight remained relatively steady, even though both groups finished the study at about the same overall weight as when they began.
"When people's weight cycled, they lost tremendous amounts of muscle along with the fat, and they didn't gain the muscle back," said Thomas Link, MD, Ph.D., professor of radiology, who led the study with co-first authors Adrian A. Marth, MD, and Gabby Joseph, Ph.D. "This tells us that understanding how to protect muscle while people are losing weight is important for overall health."
Although the study was not conducted in people taking GLP-1 drugs, Link said the insight addresses a question likely to become increasingly important as more people go on and off weight-loss therapies.
Looking beyond the scale
The researchers analyzed MRI scans and health data from 1,433 middle-aged participants in the Osteoarthritis Initiative, a long-running study of adults at risk for knee osteoarthritis. While some participants maintained a stable weight during the four-year study, others experienced repeated weight fluctuations.
Using artificial intelligence to analyze MRI scans, the team measured thigh muscle volume, fat within the muscles and fat surrounding the knee. The difference between the two groups was striking.
People whose weight repeatedly fluctuated lost nearly four times as much thigh muscle over four years as those whose weight remained relatively steady. The loss was about 3.7% of thigh muscle volume in weight cyclers, compared with about 1% in noncyclers, after accounting for age, sex, baseline BMI, physical activity, diet and other health factors.
The findings also suggest that preserving muscle during weight loss deserves as much attention as losing fat.
"We need to better understand how weight loss affects the body in ways that aren't about the number on the scale," Link said.
"Fat loss is just one piece of a much larger puzzle that includes how weight loss affects arthritis, muscle, bone and other factors," Link said. "As more people use effective weight-loss therapies, we need to be thinking about how those pieces fit together."
More information: Adrian A. Marth et al, Association of Weight Cycling with MRI-based Thigh Muscle Quality and Knee-adjacent Obesity: Osteoarthritis Initiative Data, Radiology (2026). DOI: 10.1148/radiol.253988
Provided by University of California, San Francisco
This story was originally published on Medical Xpress.
