Ultra-Processed Foods Increase Muscle Fat and Harm Muscular Health

Research published on April 14, 2026, in the journal Radiology indicates that a diet high in ultra-processed foods is associated with an increase in fat accumulation within the thigh muscles. This buildup of fat may compromise muscle quality and strength, potentially increasing the risk of chronic knee pain and permanent joint damage.

The study utilized magnetic resonance imaging (MRI) scans to analyze the thigh muscles of 615 adults. The participants had an average age of just under 60 and an average body mass index (BMI) of 27, placing them in the overweight category. While the participants did not have diabetes or rheumatoid arthritis, and had not yet developed hip or knee osteoarthritis, some possessed radiographic data indicating early stages of the joint disease.

Researchers found that those who consumed the highest amounts of ultra-processed foods—which include fast food, sugary drinks, and salty snacks—were more likely to have extra fat stored in their thigh muscles. These foods are typically characterized by high calorie counts and high levels of salt and sugar, while remaining low in the vitamins, minerals, and nutrients necessary to maintain muscle health.

The Impact of Muscle Fat on Joint Health

The accumulation of fat in the thighs is particularly concerning because these muscles provide critical support for the knee. According to the research group, poor thigh strength can accelerate the progression and development of osteoarthritis, a degenerative joint disease.

Dr. Zehra Akkaya, a researcher and consultant for the Clinical and Translational Musculoskeletal Imaging group at the University of California in San Francisco and lead author of the study, noted the broader implications of this fat accumulation.

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

Dr. Zehra Akkaya

Metabolic health refers to how the body converts food into energy. When muscle quality declines due to fat infiltration, it can signal a decline in the body’s overall ability to manage energy and glucose.

Understanding Types of Muscle Fat

The research highlights that the body stores fat in muscles in two distinct ways. Intramuscular fat consists of droplets stored directly within muscle fibers. Intermuscular fat, conversely, appears as streaks of fat that sit between healthy muscles.

Christopher Fry, co-director of the Center for Muscle Biology at the University of Kentucky, explained that intramuscular fat serves as an important energy reserve that the body uses during extraordinary physical exertion, which is why This proves common in athletes.

However, when these energy reserves are not utilized or when a person has a metabolic disease such as Type 2 diabetes, fat begins to build up as intermuscular streaks. Fry stated that while everyone had a little bit of fat between their muscles, any expansion of these streaks is detrimental to health.

Broader Cardiovascular and Metabolic Risks

The implications of muscle fat extend beyond joint stability and muscle strength. The study suggests a connection between the quality of musculoskeletal health and systemic cardiovascular risks.

Referencing separate research, the data indicates that each 1% increase in muscular fat is linked to a 7% increase in a person’s risk of cardiovascular disease. This suggests that the fat accumulation driven by ultra-processed diets may contribute to heart health issues in addition to musculoskeletal degradation.

Dr. Thomas Link, chief of the musculoskeletal imaging section at the University of California San Francisco and senior author of the study, emphasized that while the links between ultra-processed foods and diabetes or heart health are well-established, the impact on musculoskeletal health is less widely understood.

The findings suggest that limiting the intake of additive-heavy, nutrient-poor processed foods may be a key factor in preserving muscle quality and reducing the long-term risk of joint degeneration and metabolic dysfunction.