Scientists warn of dieting pattern linked to four times more muscle loss

Middle-aged individuals who repeatedly lose and regain weight suffer nearly four times the thigh muscle deterioration of those whose weight holds steady, according to research published yesterday in Radiology.

The four-year study, led by a team at the University of California, San Francisco, found that so-called yo-yo dieters experienced roughly a 3.7 per cent decline in thigh muscle volume, compared with approximately 1 per cent among non-cyclers — despite both groups finishing the study at essentially the same body 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 senior author Thomas Link, professor of radiology at UCSF.

The findings carry particular significance as GLP-1 weight-loss therapies become increasingly widespread.

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The research drew on MRI scans and health records from 1,433 adults enrolled in the Osteoarthritis Initiative, with an average age of 60.9 years and a slight majority of women.

All participants maintained overall weight stability, defined as less than a 5 per cent shift in BMI across the 48-month period.

Within that cohort, the 77 individuals whose annual BMI fluctuated most dramatically — the top tenth — were designated as weight cyclers.

An AI-driven algorithm measured thigh muscle volume, fat infiltration within the muscle, and subcutaneous fat thickness around the knee at the start and end of the study.

After adjusting for age, sex, baseline BMI, physical activity, and diet, the disparity in muscle loss was stark. Notably, changes in intermuscular fat and knee-adjacent subcutaneous fat were comparable between the two groups.

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The study itself did not examine GLP-1 medication use among its participants.

However, in an accompanying editorial, Frank W. Roemer of Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany argued that the results are directly pertinent to the pattern of weight cycling that can arise when patients start and stop GLP-1 therapies.

Roemer urged that doctors prescribing such drugs may need to track muscle strength and function more closely. He suggested that structural imaging, including MRI, could prove essential "to avoid missing the development of sarcopenia or to facilitate its earliest possible detection".

Lead author Adrian Marth acknowledged the observational nature of the work. "We do think that clinicians should pay attention not only to body weight but also to muscle health in patients with a history of repeated weight loss and regain," he said.

Priya Jaisinghani, a clinical assistant professor at NYU Grossman School of Medicine who was not involved in the research, stressed the importance of examining body composition during weight changes.

"We need to better understand how weight reduction, weight cycling, and the use of weight-management medications affect the body in ways not captured by the number on the scale, including changes in the body's form and function," she said.

She called for larger, longer-term investigations measuring muscle strength, physical function, mobility, and quality of life.

With GLP-1 prescriptions rising, Jaisinghani maintained that the objective of weight management ought to be preserving muscle and function rather than simply chasing a lower number.

"For clinicians," she said, "that means pairing evidence-based treatments with adequate nutrition and resistance training while keeping the ultimate goal in focus: helping patients live longer, healthier, and more functional lives."

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