Ultra‑processed foods and muscle

Magnetic resonance imaging can show when muscle starts looking marbled with fat instead of dense and lean, and a new Radiology study tied that pattern to higher intake of ultra-processed foods. (pubs.rsna.org) The researchers analyzed baseline data from 615 adults in the Osteoarthritis Initiative, a National Institutes of Health-backed knee study, and published the results on April 14, 2026. Participants had no radiographic knee osteoarthritis and no pain in either knee or hip at the start. (pubs.rsna.org, nda.nih.gov) Ultra-processed foods made up an average 41.4% of participants’ diets over the prior year, and higher intake tracked with more fat infiltration in thigh muscles on magnetic resonance imaging. The association held after adjustments for calories, smoking, physical activity, depression, and either body mass index or waist size. (pubs.rsna.org) The paper measured muscle fat with the Goutallier grade, a radiology scale that runs from 0 for no fatty streaks to 4 for more than 50% fatty signal. Higher ultra-processed food intake was linked to worse scores across all thigh muscles, with especially clear signals in the flexor and adductor groups. (pubs.rsna.org) Ultra-processed foods are industrial formulations built from extracted ingredients, additives, or lab-made compounds rather than mostly intact foods. In the study materials and related coverage, examples included sugary drinks, packaged snacks, hot dogs, frozen pizzas, ready-to-eat meals, breakfast cereals, and mass-produced breads and buns. (congress.gov, rsna.org, nbcnews.com) The study focused on muscle quality, not just body weight. Lead author Zehra Akkaya of the University of California, San Francisco, said the results suggest that diet quality may matter for muscle composition even when calorie intake is similar. (rsna.org, nbcnews.com) That muscle change matters in knee disease because fat inside the thigh muscles can weaken support around the joint and may raise osteoarthritis risk. The Radiological Society of North America press release and follow-up reports both pointed to knee osteoarthritis as the main concern in this cohort. (rsna.org, everydayhealth.com, newser.com) The paper does not prove that ultra-processed foods caused the fat buildup. It was a cross-sectional analysis of older data collected from February 2004 to October 2015, so it can show an association at one point in time, not a direct cause-and-effect chain. (pubs.rsna.org) Researchers also relied on a self-reported food frequency questionnaire covering the previous 12 months, which can miss or misclassify what people actually ate. And the cohort was already at risk for knee osteoarthritis, with a mean age of 59.5 years and a mean body mass index of 27, so the findings may not apply the same way to younger or lower-risk groups. (pubs.rsna.org) What the study adds is a new imaging clue: diet linked not only to weight or blood markers, but to visible fat stored inside thigh muscle. The next step is longer-term research that tracks whether changing ultra-processed food intake changes muscle composition and later knee outcomes. (pubs.rsna.org, medicalnewstoday.com)