A new study suggests that people who eat more ultraprocessed foods may have higher levels of fat stored within their thigh muscles, a change linked to muscle quality. The findings come from a study of 615 adults and add to growing research on how diet patterns may relate to body composition, not just weight.
The research, published in Radiology, analyzed data from adults around age 60 who were part of a large U.S. study on knee health. It found that higher intake of ultraprocessed foods was associated with greater fat infiltration in thigh muscles, even after accounting for factors such as physical activity, body weight and total calorie intake.
Because the study is observational, it cannot show that ultraprocessed foods directly cause these changes.
Ultraprocessed foods refer to industrially formulated products that often contain a mix of refined ingredients, additives and flavorings. In this study, they included items such as packaged snacks, sugary drinks, ready-to-eat meals and mass-produced breads.
Researchers used MRI scans to measure intramuscular fat, which appears as streaks of fat within muscle tissue. Higher levels of this fat are considered a marker of lower muscle quality and have been linked in other research to reduced strength and higher risk of joint problems.
“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prevalences of obesity and knee osteoarthritis, the use of natural ingredients in our diets has steadily diminished and been replaced by industrially-processed, artificially flavored, colored and chemically altered food and beverages, which are classified as ultraprocessed foods,” said lead author Zehra Akkaya, M.D.
Participants in the study consumed an average of 41% of their daily food from ultraprocessed sources. Those with higher intake tended to show more fatty degeneration in the thigh muscles on MRI scans. The association remained even after researchers adjusted for differences in physical activity levels and overall diet composition.
The study focused on people who were at risk for knee osteoarthritis but did not yet have the condition. That matters when interpreting the findings. The results may not apply in the same way to younger or healthier populations, and the study did not measure outcomes such as strength, mobility or pain.
“This research underscores the vital role of nutrition in muscle quality in the context of knee osteoarthritis,” Akkaya said.
The findings also highlight an important distinction. While much of the conversation around diet and health focuses on calories or weight, this study looked at where fat is stored in the body. Fat within muscle tissue is different from body fat measured by weight or BMI and may have separate implications for physical function.
At the same time, the study does not isolate which aspects of ultraprocessed foods may be driving the association. These foods vary widely in nutrient content, and the research does not determine whether the observed differences are related to processing, overall diet quality or other lifestyle factors.
This study was funded by the National Institutes of Health, including grants supporting the Osteoarthritis Initiative and additional support from the National Institute on Aging. The Osteoarthritis Initiative is a public-private research partnership.