Repeatedly losing and gaining weight may accelerate muscle loss in middle-aged people, according to new research from UC San Francisco published on July 21 in Radiology. The study comes as weight-loss medications are transforming obesity treatment.
Researchers found that participants whose weight fluctuated repeatedly lost significantly more thigh muscle over four years than those who maintained a relatively steady weight, even though both groups ended the study at about the same overall weight. "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, PhD, professor of Radiology and lead author of the study. "This tells us that understanding how to protect muscle while people are losing weight is important for overall health."
The study did not include participants taking GLP-1 drugs, but Link said these findings address questions likely to become increasingly relevant as more individuals use and discontinue weight-loss therapies.
The researchers analyzed MRI scans and health data from 1,433 middle-aged participants in the Osteoarthritis Initiative—a long-running National Institutes of Health-funded study focused on adults at risk for knee osteoarthritis. Some participants maintained stable weights during the four-year period while others experienced repeated fluctuations.
Using artificial intelligence to assess MRI scans, the team measured thigh muscle volume as well as fat within muscles and around the knee. People whose weights fluctuated lost nearly four times as much thigh muscle over four years compared to those with stable weights—about 3.7% versus about 1%, after adjusting for age, sex, baseline BMI, physical activity, diet, and other factors.
Link concluded that preserving muscle during periods of weight loss should receive attention alongside fat reduction efforts: "Fat loss is just one piece of a much larger puzzle that includes how weight loss affects arthritis, muscle, bone, and other factors," he said. "As more people use effective weight-loss therapies, we need to be thinking about how those pieces fit together."
