Most of us think of knee pain as a problem of age, weight or worn-out cartilage. But what if part of the story is sitting quietly in the snacks and ready meals we reach for every day?
- A 2026 UCSF study of 615 adults linked higher ultra-processed food intake to more fat stored inside the thigh muscles.
- The link held even after researchers accounted for total calories, physical activity and other lifestyle factors.
- Fat inside the thigh muscles may weaken the support around the knee and could raise the risk of osteoarthritis.
- On average, about 41% of what participants ate was ultra-processed.
- The study shows an association, not proof of cause, but it points to diet quality as a real factor in muscle and joint health.
Yes, eating more ultra-processed food appears to be linked with more hidden fat inside your muscles, and that may matter for your knees. A study published in the journal Radiology in 2026, led by Dr. Zehra Akkaya at the University of California, San Francisco, used MRI scans to look inside the thigh muscles of 615 adults. The more ultra-processed foods people reported eating, the more fat the scans found woven into their muscle. This was true regardless of how many calories they ate or how active they were. In simple terms, it is not only how much you eat, but what you eat, that may shape the strength of the muscles that hold your knees steady.
What the UCSF Study Actually Found
The participants came from the Osteoarthritis Initiative, a long-running research programme funded by the US National Institutes of Health. Their average age was 60, and their average BMI was 27, which falls in the overweight range. Importantly, none of them showed signs of knee osteoarthritis when their scans were analysed.
Researchers looked at what each person had eaten over the previous year and sorted those foods by how heavily they were processed. On average, around 41% of their diet came from ultra-processed items. They then used standard, widely available MRI scans to measure fat within the thigh muscles.
The pattern was clear. People who ate more ultra-processed food had more fat tucked inside their muscles. Because the team adjusted for calorie intake, physical activity and social factors, the link cannot simply be explained by people eating more or moving less.
Why Fat Inside Muscles Matters for Your Knees
We usually picture body fat as the layer under the skin or around the belly. Intramuscular fat is different. It sits inside and between muscle fibres, a bit like the white streaks you see in marbled meat. When too much of it builds up, the muscle tends to become weaker and less efficient.
The quadriceps and other thigh muscles act as shock absorbers and stabilisers for the knee joint. If those muscles lose quality, more stress may pass directly to the cartilage and bones. According to the researchers, these fatty changes may weaken support around the knee and potentially increase the risk of osteoarthritis, a joint condition the World Health Organization describes as a common cause of pain and disability in older adults.
What Counts as Ultra-Processed Food?
Ultra-processed foods are industrial products made mostly from refined ingredients plus additives such as emulsifiers, flavourings and colours. The study article names common examples: breakfast cereals, margarines and spreads, packaged snacks, hot dogs, soft drinks, energy drinks, candies, desserts, frozen pizzas, ready-to-eat meals and mass-produced breads and buns.
In Indian homes, the list often includes instant noodles, packaged namkeen and chips, cream biscuits, sweetened drinks and ready-to-cook mixes loaded with additives. These foods are convenient and tasty, which is exactly why they slowly take over a large share of the plate.
Diet Quality, Not Just Calories
The most useful message from this study is about quality. Dr. Akkaya noted that diet quality deserves more attention, and that weight-loss plans should look beyond cutting calories and exercising. Two people can eat the same number of calories, yet the one eating more ultra-processed food may carry more hidden fat in their muscles.
This fits with what we know from wider research on ultra-processed diets, which have been linked to higher risks of obesity, type 2 diabetes and heart disease. Muscle health may now be part of that picture.
A Fair Word on the Limits
This was a cross-sectional study, which means it captured a single snapshot in time. It shows that two things tend to appear together, but it cannot prove that ultra-processed food directly causes fat to build up in muscles. Most participants were also overweight, so the results may not apply equally to everyone. Longer studies that follow people over time will help confirm the link.
Simple Ways to Protect Your Muscles and Joints
You do not need a perfect diet to make a difference. Small, steady swaps add up:
- Build meals around whole foods such as dal, sabzi, whole grains, curd, eggs, nuts and seeds.
- Replace packaged chips and namkeen with roasted chana, peanuts or baked options like iHTF Baked Ragi Chips.
- Choose fresh fruit, dates or traditional sweets made without refined sugar over biscuits and desserts.
- Read labels. A long list of ingredients you would never use in your own kitchen is a good sign of heavy processing.
- Keep your thigh muscles active with walking, stair climbing and simple strength moves like sit-to-stands.
If a sweet craving strikes, a treat like our iHTF Dry Fruit Ladoo, made with dates, figs and raisins and no refined sugar, is a kinder choice for your body than a packaged dessert.
We're India Heals Through Food — and we share fresh, well-researched health and nutrition insights like this one, every single day. Follow us on Instagram and Facebook to stay updated.
Frequently Asked Questions
1. What are ultra-processed foods?
Ultra-processed foods are industrial products made mostly from refined ingredients and additives such as emulsifiers, flavourings and colours. Common examples include packaged chips, biscuits, sugary cereals, soft drinks, instant noodles, frozen pizzas and ready-to-eat meals. They are usually high in sugar, salt and refined fats, and low in fibre and natural nutrients.
2. What is intramuscular fat and why does it matter for the knees?
Intramuscular fat is fat stored inside and between muscle fibres rather than under the skin. When it builds up in the thigh muscles, the muscle tends to become weaker and less efficient. Because the thigh muscles help support and stabilise the knee, fatty changes there may raise the risk of knee osteoarthritis over time.
3. Can ultra-processed food affect muscles even if my calorie intake is normal?
A 2026 study of 615 adults, published in Radiology, found that people who ate more ultra-processed food had more fat inside their thigh muscles, even after researchers accounted for total calories and physical activity. This suggests diet quality, not only the amount eaten, may shape muscle health, though the study cannot prove cause and effect.
4. What are simple Indian swaps for ultra-processed snacks?
Easy swaps include roasted chana or peanuts instead of packaged chips, fresh fruit or dates instead of biscuits and sweets, homemade poha or upma instead of instant noodles, and plain buttermilk or nimbu pani instead of soft drinks. Choosing foods with short, familiar ingredient lists is a practical way to cut ultra-processed intake.
