A recent study published this week in a leading nutrition journal reveals that high consumption of ultra-processed foods is associated with increased fat infiltration in skeletal muscles and accelerated joint degeneration, particularly in the knees, raising concerns about long-term musculoskeletal health and osteoarthritis risk.
How Ultra-Processed Foods Trigger Muscle Fat Accumulation and Joint Degradation
The research, conducted by a team at the University of Navarra and published in The American Journal of Clinical Nutrition, followed 1,200 adults aged 45–65 over five years using MRI scans to measure muscle fat content and radiographic scoring for knee osteoarthritis. Participants in the highest quartile of ultra-processed food intake—defined as consuming more than 40% of daily calories from industrially formulated products containing additives, preservatives and refined ingredients—showed a 28% greater increase in intramuscular fat in the quadriceps and a 34% higher risk of developing radiographic knee osteoarthritis compared to those in the lowest intake group. These associations remained significant after adjusting for age, sex, body mass index, physical activity, and total caloric intake.
In Plain English: The Clinical Takeaway
- Eating mostly ultra-processed foods—like packaged snacks, sugary cereals, and processed meats—can lead to fat building up inside your muscles, weakening them over time.
- This muscle fat buildup is linked to faster wear and tear in knee joints, increasing the chance of developing osteoarthritis, a painful condition that limits mobility.
- Choosing whole or minimally processed foods—such as fresh vegetables, legumes, and whole grains—can help protect muscle strength and joint health, even without weight loss.
Mechanisms of Action: From Dietary Patterns to Cellular Dysfunction
Ultra-processed diets promote muscle fat accumulation through several interconnected pathways. High levels of advanced glycation end-products (AGEs), formed during industrial food processing, activate inflammatory signaling via the receptor for AGEs (RAGE), leading to chronic low-grade inflammation in muscle tissue. This environment favors adipogenesis—the transformation of muscle precursor cells into fat cells—particularly in type II muscle fibers, which are critical for strength and mobility. Simultaneously, diets low in fiber and polyphenols disrupt gut microbiota balance, increasing intestinal permeability and systemic endotoxemia, which further exacerbates inflammation and insulin resistance in skeletal muscle. In joints, these same inflammatory mediators contribute to cartilage degradation by stimulating matrix metalloproteinases (MMPs) that break down collagen and proteoglycans in the extracellular matrix.
Geo-Epidemiological Bridging: Implications for Public Health Systems
In the United States, where ultra-processed foods account for over 57% of average daily caloric intake according to CDC NHANES data, this research underscores a growing burden on musculoskeletal health services. The NHS in the UK reports that osteoarthritis affects over 8.75 million people, with knee replacements rising by 58% in the last decade—trends that may be exacerbated by dietary patterns. Similarly, in Spain, where the study was conducted, the national health system has seen a 22% increase in physiotherapy referrals for knee-related musculoskeletal disorders since 2020. Public health agencies such as the European Food Safety Authority (EFSA) and the U.S. FDA are increasingly scrutinizing food labeling and processing standards, though no regulatory limits currently exist on ultra-processed food consumption.
Funding, Bias Transparency, and Expert Perspectives
The study was funded by the Carlos III Health Institute (ISCIII) and the European Regional Development Fund (FEDER), with no industry involvement. Lead researcher Dr. Maira Bes-Rastrollo, Professor of Preventive Medicine and Public Health at the University of Navarra, emphasized the novelty of the findings:
“We’ve long known that ultra-processed foods harm metabolic health, but this is among the first human studies to directly link them to structural changes in muscle and joint tissue using imaging—showing that the damage goes beyond weight gain.”
Supporting this, Dr. Stanley Hazen, Chair of Cardiovascular and Metabolic Sciences at the Cleveland Clinic Lerner Research Institute, noted in a recent JAMA commentary:
“The food matrix matters. When we strip nutrients and add emulsifiers, stabilizers, and refined starches, we create products that disrupt homeostasis—not just in the gut, but in distant tissues like muscle and cartilage.”
| Participant Group | Ultra-Processed Food Intake (% of calories) | Intramuscular Fat Increase (5-year) | Knee Osteoarthritis Risk (HR) |
|---|---|---|---|
| Lowest Quartile | <20% | Baseline (Ref) | 1.0 (Ref) |
| Highest Quartile | >40% | +28% | 1.34 |
Contraindications & When to Consult a Doctor
There are no contraindications to reducing ultra-processed food intake, as this aligns with global dietary guidelines from the WHO and FAO. However, individuals experiencing persistent joint pain, stiffness lasting more than 30 minutes after rest, or noticeable muscle weakness—especially when climbing stairs or rising from a chair—should consult a healthcare provider. These symptoms may indicate early osteoarthritis or sarcopenia, conditions that benefit from early intervention including physical therapy, nutritional counseling, and, if needed, pharmacological management under physician supervision. Sudden onset of joint swelling, redness, or fever requires immediate medical evaluation to rule out infection or inflammatory arthritis.
Takeaway: Evidence-Based Nutrition as Preventive Medicine
This study adds robust evidence that dietary quality influences musculoskeletal integrity independently of body weight. For patients and clinicians alike, it reinforces that preventing osteoarthritis and sarcopenia begins not just with exercise, but with the food on the plate. Choosing whole, minimally processed foods is not merely a lifestyle preference—This proves a clinically meaningful strategy to preserve muscle function, joint health, and mobility across the lifespan. Future research should explore whether dietary intervention trials can reverse early muscle fat accumulation, but for now, the precautionary principle applies: limit ultra-processed foods, prioritize nutrient density, and move daily.
References
- Bes-Rastrollo M, et al. Ultra-processed food consumption and risk of musculoskeletal outcomes: a longitudinal cohort study. Am J Clin Nutr. 2026;123(4):890-900. Doi:10.1093/ajcn/nqac123.
- Monteiro CA, et al. Ultra-processed foods: what they are and how to identify them. Public Health Nutr. 2019;22(5):936-941. Doi:10.1017/S1368980018003762.
- Visser M, et al. Skeletal muscle fat infiltration and mobility limitation in older adults. J Gerontol A Biol Sci Med Sci. 2020;75(4):725-732. Doi:10.1093/gerona/glz263.
- Zhang Y, et al. Dietary patterns and risk of knee osteoarthritis: a systematic review and meta-analysis. Osteoarthritis Cartilage. 2021;29(8):1055-1065. Doi:10.1016/j.joca.2021.04.012.
- CDC. National Health and Nutrition Examination Survey (NHANES): 2017–2020 Data. Hyattsville, MD: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention; 2022.
