Muscle health, unlike muscle building, isn't something most people think about until it starts to decline. New research suggests diet may be shaping that decline earlier than expected.
Researchers report that diets high in ultra-processed foods are connected with poorer muscle quality, as evidenced by increased fat inside the thigh muscles. The findings raise concerns about how modern eating patterns may influence strength, mobility and the aging process.
Ultra-processed foods, or UPFs, are items such as packaged snacks, sugary drinks, processed meats and ready-to-eat meals. They are industrial formulations made largely from refined ingredients, additives and preservatives. These foods are often high in salt, sugar and unhealthy fats, while lacking the protein and micronutrients muscles need to maintain structure, strength and function.
To investigate the connection between diet and muscle health, researchers analyzed data from 615 adults enrolled in the Osteoarthritis Initiative, a long-term U.S. study. Participants were, on average, 60-years-old and considered overweight, with a mean body mass index of 27.Diets high in ultra-processed foods are associated with poorer muscle quality.
None had been diagnosed with knee osteoarthritis at the start of the study, but all were considered at risk.
Participants' dietary intake of processed foods was assessed using detailed food frequency questionnaires covering the previous year. Researchers then classified foods using the NOVA system to estimate how much of each participant's diet came from ultra-processed sources. On average, these foods accounted for about 40 percent of their daily calorie intake.
The structural quality of a participant's muscles was evaluated through a magnetic resonance image (MRI) of their thigh. The researchers focused on how much fat was present within muscle tissue, with greater fat infiltration being considered a sign of poor muscle quality and linked to reduced strength and function.
The results were consistent: higher consumption of ultra-processed foods was associated with greater fat infiltration across multiple thigh muscle groups. This relationship held even after adjusting for body weight, physical activity, total calorie intake, smoking status, as well as other demographic and health factors.
The association was even stronger when researchers accounted for abdominal fat, suggesting that where fat is stored in the body may play a role in muscle quality. The relationship was linear, as ultra-processed food intake increased, so did fat within the muscle. The pattern was observed in both men and women.
Among specific muscle groups, the strongest association was seen in the abductors, while the flexors showed the highest overall fat infiltration. The findings were consistent across multiple analyses, which strengthened confidence in the results.
Lead author Zehra Akkaya, MD, a researcher and consultant with the Clinical and Translational Musculoskeletal Imaging group at the University of California, San Francisco, emphasized the broader implications in a press release: “Muscles with lots of fat stored have poor quality, and this is concerning not only because it indicates poorer muscle strength but also worse overall metabolic health.”
That distinction matters. Thigh muscles play a critical role in stabilizing the knee joint. When muscle quality declines, it can increase the risk of pain, reduce mobility and lead to the progression of osteoarthritis. Previous studies have linked processed food intake to worse knee symptoms. This research suggests a structural explanation.High consumption of ultra-processed foods was associated with greater fat infiltration across multiple thigh muscle groups.
The study has limitations. Because it is observational, it cannot prove that ultra-processed foods directly cause muscle deterioration. It is also possible that people who consume more of these foods have overall poorer diets, including lower intake of fruits, vegetables and whole grains.
The findings add to a growing body of evidence linking ultra-processed diets to negative health outcomes. For consumers, the takeaway is less about eliminating specific foods and more about improving overall dietary patterns.
Muscle health depends on adequate protein, nutrients and metabolic balance. All these factors are more reliably found in whole or minimally processed foods. Over time, those choices may influence not just how we look or feel, but how we move.
The study is published in Radiology
