Ultra‑processed food and muscle fat

Magnetic resonance imaging can spot fat streaks inside muscle the way it spots damage in a knee, and a new Radiology study linked more ultra-processed food to more of that hidden thigh fat. (pubs.rsna.org) The study, published April 14, 2026, analyzed baseline data from 615 people in the Osteoarthritis Initiative, a National Institutes of Health-backed cohort. Participants had no radiographic osteoarthritis and no knee or hip pain at the time of imaging. (pubs.rsna.org) Researchers used thigh magnetic resonance imaging scans and graded muscle fat infiltration on a 0-to-4 scale, from no fatty streaks to more than 50% fatty signal. They estimated each person’s ultra-processed food intake from a food-frequency questionnaire covering the prior 12 months and classified foods with the NOVA system. (pubs.rsna.org) On average, ultra-processed foods made up 41.4% of participants’ diets, and higher intake tracked with more fat infiltration across all thigh muscles. The association held after researchers adjusted for calories, smoking, physical activity, depression, body mass index, and abdominal circumference. (pubs.rsna.org) That matters because thigh muscles help stabilize the knee, and weaker, fattier muscle has been tied to osteoarthritis outcomes in earlier imaging research. A 2022 Radiology study found that people with knee osteoarthritis had more intramuscular fat over time, and those changes were linked to worse clinical outcomes. (pubs.rsna.org) The new paper did not show that ultra-processed foods directly caused muscle fat or arthritis. It was a cross-sectional analysis, meaning diet and magnetic resonance imaging were measured at the same point rather than followed forward to prove cause and effect. (pubs.rsna.org) Ultra-processed foods in this study included items such as breakfast cereals, packaged snacks, hot dogs, soft drinks, candy, frozen pizza, ready-to-eat meals, and mass-produced breads and buns. The authors said these products are typically built from industrial ingredients and additives rather than mostly intact foods. (rsna.org) The findings land as ultra-processed foods still dominate American diets. Centers for Disease Control and Prevention data for August 2021 through August 2023 put the average at 53.0% of calories for adults and 61.9% for youth ages 1 to 18. (cdc.gov) Outside experts said the thigh result may not be limited to the thigh. Miriam Bredella of New York University Langone Health, who was not involved in the study, told CNN that fat infiltration seen in one major muscle group usually reflects a broader body-wide process. (keyt.com) The next step is not another food list but longer follow-up. Researchers need to test whether people who cut back on ultra-processed foods show less muscle fat on later scans and lower odds of knee osteoarthritis. (pubs.rsna.org)