A new wave of scientific evidence has uncovered a silent but alarming effect of ultra-processed foods (UPFs)—the kind found in sweet snacks, packaged meals, and fast-food chains. While these foods are already notorious for triggering weight gain and metabolic issues, the latest findings reveal a deeper danger: they may be quietly weakening the very muscles that protect your knees.
Recent research has shown that UPFs increase intramuscular fat—a type of fat that infiltrates and spreads inside your thigh muscles. What makes this discovery more concerning is that this buildup was observed even in people who were not overweight, and even in those who exercised regularly.
What the Study Found
Researchers analyzed MRI scans of 666 adults, studying the composition of their thigh muscles. Individuals with a higher intake of ultra-processed foods had significantly more fat inside their muscles, regardless of their daily calorie intake or physical activity levels. In other words, even if you “eat less” or go for daily walks, a diet rich in processed foods can still change how your muscles function internally.
This intramuscular fat gradually replaces healthy muscle fibers, reducing strength, stability, and shock absorption capacity. As a result, the legs—especially the quadriceps—become less effective at supporting and protecting the knees.
Why This Matters for Your Knees
The thigh muscles are the primary support system for the knee joint. When these muscles weaken, the knees take on more stress with every step, jump, or even simple daily movement. Over time, this extra strain accelerates the wear and tear of joint cartilage, increasing the risk of knee pain, mobility problems, and early osteoarthritis.
Experts point to the high sugar content, harmful fats, and chemical additives in UPFs as the triggers. These ingredients promote inflammation, disrupt metabolic processes, and increase insulin resistance, all of which contribute to fat accumulation inside muscle tissues.
The Good News
The damage isn’t irreversible. Studies suggest that improving your diet—reducing ultra-processed foods and eating more whole, fresh meals—can lower intramuscular fat and help your muscles regain strength. While joint damage cannot be completely reversed, better nutrition and lifestyle choices can significantly slow progression and reduce pain.
Bottom Line
Cut the processed foods. Strengthen your muscles. Protect your knees.