Ultraprocessed foods do more than add extra pounds. A new study reveals they also weaken muscles, as fat increases and strength decreases. Even if calorie intake stays the same, people who eat more ultraprocessed foods develop higher fat deposits in their thigh muscles. This hidden fat may set the stage for knee osteoarthritis, the most common form of arthritis.
“In an adult population at risk for but without knee or hip osteoarthritis, consuming ultraprocessed foods is linked to increased fat within the thigh muscles,” said Zehra Akkaya, study co-author and researcher in the Department of Radiology and Biomedical Imaging at the University of California, San Francisco, in a statement. “These findings held true regardless of dietary energy content, [body mass index], sociodemographic factors or physical activity levels.” The results of the study were presented at the annual meeting of the Radiological Society (RSNA) of North America.
How Junk Food Sneaks Into Muscles
Ultraprocessed foods, convenience foods high in sugar, salt, refined fats and preservatives, are a staple of modern diets. They include breakfast cereals, frozen meals, sodas, candies, packaged snacks and mass-produced breads. Their combination of flavors, additives and easy access makes them hard to resist.
Researchers analyzed ultraprocessed food intake and MRI scans from the 666 study participants, all part of the Osteoarthritis Initiative, a longitudinal osteoarthritis study sponsored by the National Institutes of Health. The group included men and women with an average age of 60 and an average body mass index (BMI) of 27, placing them in the overweight category. None had been diagnosed with osteoarthritis.
The research results showed that the more ultraprocessed foods in someone’s diet, the more intramuscular fat they had in place of healthy thigh muscle. This shift occurred regardless of how many calories they consumed. “On MRI images, this decline can be seen as fatty degeneration of the muscle, where streaks of fat replace muscle fibers,” Akkaya explained.
Weak Muscles, Bad Knees
Strong muscles protect joints. They absorb impact, stabilize movement and reduce strain on cartilage. However, when fat replaces muscle, the support system collapses. Weak thighs put extra stress on knee joints, increasing wear and tear. “Research from our group and others has previously shown that quantitative and functional decline in thigh muscles is potentially associated with onset and progression of knee osteoarthritis,” Akkaya said.
Inflammation and the Junk Food Trap
The impact of ultraprocessed foods goes beyond fat deposits. “All of these processed foods trigger the release of pro-inflammatory substances,” explained Paul Arciero, a professor in the Health and Human Physiological Sciences Department at Skidmore College in Saratoga Springs, New York. “These substances also increase pain,” said Arciero, who was not involved in the study.
A Preventable Crisis
Osteoarthritis is a growing global health burden, driving up medical costs and reducing quality of life. “It is the largest contributor to non-cancer related health care costs in the United States and around the world,” Akkaya noted. But prevention remains within reach. Understanding the relationship between ultraprocessed food and muscle “could have important clinical implications, as it offers a new perspective on how diet quality affects musculoskeletal health,” Akkaya said.
By reducing their intake of ultra-processed foods, strengthening muscles, and maintaining a healthy weight, people can rebuild lost muscle mass and help to reduce their risk of arthritis.
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