• Posted April 17, 2026

Ultra-Processed Foods Linked To Fatty Muscles, Potential Knee Arthritis

Ultra-processed foods don't just contribute to flab around your middle, but also to fat inside your muscles, a new study has found.

A diet high in ultra-processed foods is associated with larger amounts of fat stored inside thigh muscles, regardless of a person’s calorie or fat intake, researchers reported April 14 in the journal Radiology.

MRI scans showed streaks of fat replacing muscle fibers, contributing to degeneration of the thigh muscle, researchers said.

People with fatty thigh muscles could be at a higher risk for developing knee arthritis, researchers said.

“This research underscores the vital role of nutrition in muscle quality in the context of knee osteoarthritis,” lead researcher Dr. Zehra Akkaya, a radiologist at the University of California-San Francisco, said in a news release.

“Osteoarthritis is an increasingly prevalent and costly global health issue,” she said. “It constitutes one of the largest non-cancer-related health care costs in the United States and around the world. It is highly linked to obesity and unhealthy lifestyle choice.”

Ultra-processed foods are made mostly from substances extracted from whole foods, like saturated fats, starches and added sugars. They contain a wide variety of additives to make them more tasty, attractive and shelf-stable.

Examples include packaged baked goods, sugary cereals, soft drinks, deli cold cuts, as well as ready-to-eat or ready-to-heat products.

“Over the past decades, in parallel to the rising prevalences of obesity and knee osteoarthritis, the use of natural ingredients in our diets has steadily diminished and been replaced by industrially-processed, artificially flavored, colored and chemically altered food and beverages, which are classified as ultra-processed foods,” Akkaya said.

Previous research has shown that ultra-processed foods are linked to an overall increased risk of excess weight. 

These foods contribute 58% of people’s calorie intake and 89% of the added sugars in their diet, researchers said in background notes.

For the new study, researchers analyzed data from 615 participating in a federally funded long-term arthritis research project. None had yet been affected by osteoarthritis, which is caused by the normal wear-and-tear of aging.

The average age of participants was 60, and they tended to be overweight, with a body mass index (BMI) of 27. (BMI is an estimate of body fat based on height and weight.) About 41% of the food they ate the prior year was ultra-processed.

MRI scans revealed that the higher a person’s intake of ultra-processed food, the more fat they had stored in between the muscle fibers of their thigh muscles. This association held regardless of a person’s overall calorie intake.

The scans showed streaks of fat replacing muscle fibers, causing degeneration of the thigh muscle.

“Addressing obesity is a primary objective and frontline treatment for knee osteoarthritis, yet the findings from this research emphasize that dietary quality warrants greater attention, and weight loss regimens should take into account diet quality beyond caloric restriction and exercise,” Akkaya said.

She noted that the approach used to assess muscle quality is one that could be easily adopted by doctors and health systems.

“We used widely available, non-enhanced MRI, making our approach accessible and practical for routine clinical use and future studies,” Akkaya said. “These MRIs do not require advanced or costly technology, which means they can be easily incorporated into standard diagnostic practices.”

More information

The Arthritis Foundation has more on how fat can worsen arthritis.

SOURCES: Radiological Society of North America, news release, April 14, 2026; Radiology, April 14, 2026