Ultraprocessed Foods Tied to Fat Stored in the Thighs

People who eat lots of ultraprocessed foods may end up with more fat in their thigh muscles and a higher risk of knee pain, a new study suggests.

Eating lots of ultraprocessed foods may increase the amount of fat in your muscle tissue — even when you exercise regularly and don’t consume an excessive number of calories, according to a new study.

The association between higher consumption of ultraprocessed foods and what’s called fatty degeneration of muscle tissue persisted even after researchers accounted for numerous other factors that could have affected the study results.

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“These findings held true regardless of dietary energy content [calorie intake], BMI [body mass index], sociodemographic factors, or physical activity levels,” said study author Zehra Akkaya, MD, a researcher and former Fulbright Scholar in the department of radiology and biomedical imaging at the University of California in San Francisco, in a statement.

The study was presented at the annual meeting of the Radiological Society of North America and has not yet been published in a medical journal or peer reviewed, a process that typically allows independent experts to verify the validity of the findings. 

How Ultraprocessed Foods Affect Muscle Tissue

The researchers examined data on nearly 700 adults who completed dietary questionnaires and underwent magnetic resonance imaging (MRI) exams of their thighs to assess the amount of fat accumulation in the muscle tissue. Participants were 60 years old on average and typically overweight based on their BMI. 

Approximately 40 percent of the foods people ate in the previous year were ultraprocessed — meaning they contained few, if any, ingredients from whole plant or animal foods and were industrially processed, artificially flavored or colored, or chemically altered.

A wide variety of mass-produced foods can be ultraprocessed. These can include breakfast cereals, margarines, packaged snacks, hot dogs, soft drinks and energy drinks, candies and desserts, frozen pizzas, ready-to-eat meals, and mass-produced breads. 

People whose diets contained the highest amounts of ultraprocessed foods had significantly more fat accumulation within their thigh muscle tissue than individuals who consumed the smallest amounts of ultraprocessed foods. 

To illustrate the impact of ultraprocessed foods on muscle tissue quality, researchers shared detailed findings for two female study participants who were both obese. Ultraprocessed foods made up 68 percent of one woman’s diet and her muscle tissue contained significantly more fat than the other woman, whose diet contained only 36 percent ultraprocessed foods. 

Excess Fat in Thigh Muscles Could Increase the Risk of Knee Osteoarthritis

Researchers noted that the excess fat within thigh muscle tissue might add to participants’ risk of knee osteoarthritis, or degeneration in the knee joints that is more common among people who are overweight or have obesity. 

Reducing intake of ultraprocessed foods might be one way to decrease the risk of developing knee osteoarthritis, Dr. Akkaya said in the statement. 

For a Healthy Body, Focus on Whole Foods and Lean Protein

There is a clear connection between muscle tissue quality and diet, says Connie Diekman, RD, LD, a food and nutrition consultant and past president of the Academy of Nutrition and Dietetics, who wasn’t involved in the new study. 

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“Muscle mass requires adequate calories and protein,” Diekman says. “Choosing lower nutritional quality foods will make it harder for the body to maintain adequate muscle mass, making it easier for fat deposition in those muscles. Weaker muscles are key contributors to poor joint health and pain.”

The best way to eat for healthy muscles involves getting lots of carbohydrates from whole grains, whole fruits and vegetables, and protein from lean animal sources balanced with plant-based protein like beans, nuts, and seeds, Diekman says. 

“The quality of muscle in the body, along with bone health, does align with how we fuel the body,” Diekman says. “If we choose lower nutrient choices going in, the health of the body will be negatively impacted.”