Ultra-processed foods have long been associated with significant health risks, including obesity, diabetes, heart disease, and cancer. Recent images, however, starkly reveal the internal havoc these foods can wreak on the human body.

A striking case study has brought this issue into sharp focus, showcasing an image that resembles a cut of steak more than it does a human thigh. This unsettling photo highlights the severe damage ultra-processed foods (UPFs) can inflict.

The individual in the photograph derived a staggering 87 percent of her nourishment from UPFs. These foods are primarily industrial concoctions, consisting of components like refined sugars, oils, and starches, as well as additives such as artificial flavors, colors, emulsifiers, and preservatives.

Her diet was dominated by cold cereals, chocolate candy bars, and regular soda. Despite maintaining a moderate level of physical activity, the excessive intake of UPFs led to her leg muscles developing a marbled, steak-like appearance.

Unfortunately, she is not alone in experiencing the detrimental effects of a diet rich in UPFs. Another study involving 615 adults who were at risk of knee osteoarthritis found that these foods made up approximately 41 percent of their daily caloric intake on average.

Researchers found that higher UPF consumption was linked to greater ‘marbling’ —fat that accumulates within the thigh muscles themselves, directly replacing healthy muscle tissue and weakening the muscle.

This hidden fat also puts people at an unhealthy weight. Greater fat accumulation in the muscles is linked to higher overall body fat and increased risk of metabolic disease.

In everyday life, fattier thigh muscles make climbing stairs, rising from a chair, carrying groceries, or walking briskly more difficult. Unsteadiness raises the risk of falls, and over time, the weakness leads to a more sedentary lifestyle, accelerating muscle loss and affecting independence. 

Even with regular exercise, a diet high in ultra-processed foods can lead to fat infiltrating the thigh muscles, weakening them from the inside. This could make activities like climbing stairs or carrying groceries harder over time (stock)

The condition in which fat accumulates in muscle fibers is called myosteatosis.

In the presence of certain metabolic stressors, such as a diet high in ultra-processed foods, chronic low-grade inflammation or insulin resistance, fat cells begin to accumulate between and inside the muscle fibers.

Normally, healthy muscle tissue is composed of long, lean fibers that contract and generate force, but when the body is overloaded with refined sugars, unhealthy fats and chemical additives, the muscle tissue becomes inflamed. 

Muscle cells also stop responding properly to insulin, meaning they cannot take up glucose for energy. 

Instead of repairing muscle tissue or supporting healthy muscle fibers, specialized cells within the muscle get confused and start turning into fat cells. 

The result is that pockets of fat develop where the contracting muscle used to be, essentially replacing the muscle itself. This directly weakens the muscle and impairs its ability to move, stabilize joints, and generate power. 

The condition is not just about strength. Myosteatosis has been linked to several serious health problems. Studies show that people with fattier muscles have higher rates of insulin resistance, metabolic syndrome and chronic inflammation. 

They are also at greater risk of hospitalization, surgical complications, and even earlier death, particularly in those with liver disease, kidney disease, or cancer. 

MRI scans of two women of similar age and weight. (A) A 61-year-old who ate a diet with 30 percent ultra-processed foods. Her thigh muscles show minimal fat infiltration (marbling). (B) A 62-year-old who got 87 percent of her diet from ultra-processed foods. Her thighs appear noticeably fattier with more white streaks replacing healthy muscle tissue

The white streaks in this steak are fat. The same kind of fat infiltration — called marbling — can accumulate inside human thigh muscles when a diet is high in ultra-processed foods, directly weakening muscle tissue (stock)

Researchers used data from the Osteoarthritis Initiative, a large study that followed people at risk for knee arthritis. They narrowed thousands of participants down to 615 people who did not already have arthritis, joint pain, or other chronic diseases. 

Each participant completed a detailed questionnaire about everything they had eaten in the past year. Using a classification system, the researchers calculated what percentage of each person’s daily diet came from ultra-processed foods. 

Each participant also underwent an MRI scan of their thighs. On those scans, researchers graded fat infiltration in the thigh muscles — including the hamstrings, quadriceps and inner thighs — on a scale from zero, which was no fat, to four, meaning more than 50 percent fat. 

The study, published in the journal Radiology, found that people who consumed higher amounts of UPFs had significantly more intramuscular fat, particularly in the thighs.

For every increase in UPF consumption, muscle fat levels rose accordingly. 

This held true for all muscle groups studied, including the hamstrings, quadriceps and inner thighs. The link was even stronger when researchers looked at belly size, or abdominal circumference, rather than just BMI. 

The most affected muscles were the inner thighs (adductors) followed by the hamstrings (flexors). The quadriceps (extensors) showed the smallest but still significant effect. These results were the same for both men and women.

While researchers cannot yet say with certainty that cutting out UPFs will reverse existing muscle fat infiltration, there is good evidence that exercise and sustained weight loss can improve muscle quality.

UPFs are industrial products made from extracted substances like refined sugars, oils, and starches, plus artificial flavors, colors and preservatives (stock)

Exercise is the most promising intervention. Several studies have shown that regular aerobic exercise, such as walking 30 to 60 minutes most days, can reduce intramuscular fat in older adults, even without significant weight loss. 

Resistance training improves muscle strength and function even if fat deposits remain.

Weight loss through bariatric surgery has also been shown to reduce intramuscular fat in severely obese patients, suggesting that significant metabolic changes can reverse some of the damage.

More importantly, reducing UPF intake almost certainly stops further damage and protects muscle health as a person ages. For most people, the goal should be preventing additional marbling while building lean muscle through strength training.