Radiology, April 2026 | Zehra Akkaya et al., University of California San Francisco | Osteoarthritis Initiative
A diet high in ultra-processed food has now been associated with greater fat infiltration inside muscle tissue, a form of degradation that research has linked to reduced strength and accelerated joint deterioration.
Researchers analyzed MRI scans from 615 adults with an average age of 60, all at risk for knee osteoarthritis. Using a standardized grading system, they measured fat infiltration across the major thigh muscle groups and cross-referenced it with diet data from a food frequency questionnaire covering the preceding 12 months.
The association held firm across every major thigh muscle group and survived adjustment for BMI, abdominal circumference, physical activity, smoking, and total daily calories. It was equally evident in men and women.
That independence from weight and calorie intake is what makes the finding notable. A person can be at a healthy weight and exercise regularly while still accumulating fat inside muscle tissue if ultra-processed foods make up a large share of their diet. Calorie count alone doesn’t capture everything that processing does to food or to the body.
The finding extends ultra-processed food’s documented harms past the heart and the waist. What a person eats shapes muscle at a structural level, in ways nutrition labels don’t show.
