Ultra-processed foods linked to hidden muscle fat that may threaten your knees

The findings were published in Radiology, a journal of the Radiological Society of North America (RSNA). Higher levels of fat within thigh muscles may potentially contribute to a greater risk of developing knee osteoarthritis.

Why Ultra-Processed Foods Matter

Ultra-processed foods are often designed to be convenient, appealing, and long-lasting. They frequently combine sugar, fat, salt, and carbohydrates in ways that stimulate the brain's reward system, which can make them difficult to stop eating.

Examples include breakfast cereals, margarines/spreads, packaged snacks, hot dogs, soft drinks and energy drinks, candies and desserts, frozen pizzas, ready-to-eat meals, mass-produced packaged breads and buns. These products also typically contain synthesized ingredients.

"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prevalences of obesity and knee osteoarthritis, the use of natural ingredients in our diets has steadily diminished and been replaced by industrially-processed, artificially flavored, colored and chemically altered food and beverages, which are classified as ultra-processed foods," said the study's lead author, Zehra Akkaya, M.D., researcher and consultant for the Clinical & Translational Musculoskeletal Imaging group at the University of California, San Francisco, Department of Radiology and Biomedical Imaging.

Dr. Akkaya and her colleagues wanted to determine whether eating more ultra-processed foods was associated with changes in the amount of fat stored within thigh muscles.

Studying People at Risk for Knee Osteoarthritis

The researchers examined data from 615 participants in the Osteoarthritis Initiative who showed no signs of osteoarthritis on imaging at the time of the analysis. The Osteoarthritis Initiative is a nationwide research program sponsored by the National Institutes of Health that is designed to improve understanding of how knee osteoarthritis develops and how it might be prevented or treated.

"Osteoarthritis is an increasingly prevalent and costly global health issue," Dr. Akkaya 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 choices."

Among the 615 participants (275 men, 340 women), the average age was 60. The group had an average body mass index (BMI) of 27, placing the typical participant in the overweight range.

Based on dietary information covering the previous year, approximately 41% of the food consumed by participants was classified as ultra-processed.

More Ultra-Processed Food, More Fat Inside Muscle

The researchers found a clear association between ultra-processed food consumption and fat stored within thigh muscles. The more ultra-processed foods a person reported eating, the more intramuscular fat researchers detected, regardless of total calorie intake.

On MRI scans, this change appears as fatty degeneration of muscle tissue. Instead of muscle fibers making up the tissue uniformly, streaks of fat begin appearing within the muscle.

"In addition to investigating the quality of our modern diet in relationship to thigh muscle composition, in this study, we used widely available, non-enhanced MRI, making our approach accessible and practical for routine clinical use and future studies," Dr. Akkaya said. "These MRIs do not require advanced or costly technology, which means they can be easily incorporated into standard diagnostic practices."

The findings add to growing evidence that diet quality may influence body composition in ways that are not fully captured by measurements such as body weight or calorie intake.

Diet Quality May Matter Beyond Calories

"This research underscores the vital role of nutrition in muscle quality in the context of knee osteoarthritis," Dr. Akkaya said. "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."

Managing lifestyle factors that can be changed has long been central to the early treatment and prevention of knee osteoarthritis. That typically includes maintaining a healthy weight through a balanced diet and regular exercise.

The new findings suggest that the type of food a person eats may also deserve closer attention. Cutting back on ultra-processed foods could potentially help preserve muscle quality, which in turn may help reduce some of the burden associated with knee osteoarthritis.

"In recent years, several researchers have shown detrimental impacts of ultra-processed food on various health outcomes but data on the relationship of ultra-processed food and body composition in the context of knee osteoarthritis is limited," Dr. Akkaya said. "This is the first study assessing ultra-processed food's impact on thigh muscle composition using MRI. By exploring how ultra-processed food consumption impacts muscle composition, this study provides valuable insights into dietary influences on muscle health."