Ultra-processed foods linked to hidden thigh muscle fat, possible knee risk

Eating large amounts of ultra-processed foods may be associated with higher levels of fat stored inside thigh muscles, potentially increasing the risk of knee osteoarthritis, according to a new study.

Researchers found that people at risk of knee osteoarthritis who consumed more ultra-processed foods tended to have more fat within their thigh muscles. The association remained even after researchers considered calorie and fat intake, physical activity and sociodemographic factors.

The findings were published in Radiology, a journal of the Radiological Society of North America.

Ultra-processed foods are generally made to be convenient, attractive and long-lasting. They often contain combinations of sugar, fat, salt and carbohydrates that can stimulate the brain's reward system and encourage overeating.

Examples include breakfast cereals, spreads and margarines, packaged snacks, hot dogs, soft and energy drinks, sweets and desserts, frozen pizzas, ready-to-eat meals and mass-produced packaged bread and buns. They also commonly contain industrially produced 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prevalences of obesity and knee osteoarthritis, the use of natural ingredients in our diets has steadily diminished and been replaced by industrially-processed, artificially flavored, colored and chemically altered food and beverages," said lead author Zehra Akkaya, a researcher and consultant with the Clinical & Translational Musculoskeletal Imaging group at the University of California, San Francisco.

Akkaya and her colleagues examined whether greater consumption of ultra-processed foods was linked to changes in thigh muscle composition.

Study examines people at risk of knee osteoarthritis
The researchers analyzed data from 615 participants in the Osteoarthritis Initiative who showed no signs of osteoarthritis on imaging when the analysis was conducted.

The participants included 275 men and 340 women, with an average age of 60. Their average body mass index was 27, which falls within the overweight range.

The Osteoarthritis Initiative is a US research program supported by the National Institutes of Health that seeks to improve understanding of how knee osteoarthritis develops and how it can be prevented or treated.

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

Based on participants' dietary records from the previous year, about 41% of the food they consumed was classified as ultra-processed.

More ultra-processed food linked to more muscle fat
The study found a clear association between ultra-processed food consumption and the amount of fat stored within thigh muscles.

Participants who reported eating more ultra-processed foods tended to have higher levels of intramuscular fat, regardless of their overall calorie intake.

MRI scans can show the change as fatty degeneration of muscle tissue, in which fat begins to appear between muscle fibers rather than the tissue being made up primarily of muscle.

Akkaya said the researchers used widely available, non-enhanced MRI scans, which could make the approach practical for routine medical use and future research.

"These MRIs do not require advanced or costly technology, which means they can be easily incorporated into standard diagnostic practices," she said.

The findings add to growing evidence that diet quality may affect body composition in ways that are not fully reflected by body weight or calorie intake alone.

Diet quality may matter beyond calories
The researchers said the findings highlight the importance of nutrition when considering muscle health and knee osteoarthritis.

"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," Akkaya said.

Early prevention and treatment of knee osteoarthritis often focus on lifestyle changes, including maintaining a healthy weight through a balanced diet and regular exercise.

The new findings suggest that the types of foods people eat may also deserve greater attention. Reducing ultra-processed foods could potentially help maintain muscle quality and may reduce some of the burden linked to knee osteoarthritis.

Akkaya noted that previous research has linked ultra-processed foods to several negative health outcomes, but evidence about their relationship with body composition in the context of knee osteoarthritis remains limited.

"This is the first study assessing ultra-processed food's impact on thigh muscle composition using MRI," she said. "By exploring how ultra-processed food consumption impacts muscle composition, this study provides valuable insights into dietary influences on muscle health.