A large new study from Germany has found that hidden fat buried deep inside muscles may reveal important warning signs about a person’s future health.
Using artificial intelligence and MRI scans, researchers discovered that people with more hidden muscle fat were more likely to have high blood pressure, unhealthy cholesterol levels, and abnormal blood sugar levels—even when they had no known medical problems.
The findings were published in the journal Radiology and could eventually change how doctors screen for heart disease and metabolic disorders in the future.
Many people think body fat only exists under the skin or around the stomach. But scientists now know that fat can also collect inside muscles.
This hidden fat is called intermuscular adipose tissue, or intermuscular fat.
Unlike visible body fat, this type of fat is harder to notice without medical imaging. Researchers believe it may quietly affect the body in harmful ways for many years before symptoms appear.
The study was led by Dr. Sebastian Ziegelmayer, a radiologist and associate professor at the Technical University of Munich. His team wanted to better understand how muscle composition affects cardiometabolic health.
Cardiometabolic health includes conditions involving the heart, blood vessels, blood sugar, metabolism, and cholesterol. Diseases such as hypertension, diabetes, obesity, and heart disease all belong to this group.
Scientists have learned that skeletal muscles do much more than simply help the body move. Muscles also help regulate blood sugar, energy use, inflammation, and overall metabolism. Healthy muscle tissue may therefore protect people against many chronic diseases.
To investigate this idea, researchers examined MRI scans from 11,348 adults with no known major illnesses. The participants were scanned at five imaging centers. About 57% of participants were men, and the average participant was in their early forties.
MRI scans create detailed images of structures inside the body using magnets rather than radiation. The researchers focused on muscles running along the spine between the neck and pelvis. These muscles, called paraspinal muscles, are important for posture and movement.
The scientists used a deep learning computer model to analyze the MRI images. Deep learning is a form of artificial intelligence that can identify patterns in large amounts of data.
Using a segmentation algorithm, the researchers measured the amount of lean muscle tissue and hidden fat inside the muscles. In the past, this kind of analysis required specialists to manually review scans one by one, which took enormous amounts of time.
Artificial intelligence allowed the team to analyze thousands of scans much faster and more accurately.
Researchers then compared the muscle findings with participants’ blood pressure, blood sugar, cholesterol levels, and physical activity records.
The results showed that many people who believed they were healthy already had hidden cardiometabolic problems.
More than 16% of participants had previously undiagnosed high blood pressure. Around 8.5% had abnormal blood sugar levels, and nearly 46% had unhealthy lipid levels. Lipids are fatty substances in the blood, including cholesterol and triglycerides.
One major pattern quickly became clear. People with more hidden fat inside their muscles were much more likely to have these unhealthy conditions.
Higher intermuscular fat was linked to greater risks of hypertension, poor blood sugar control, and unhealthy cholesterol levels in both men and women.
At the same time, greater amounts of lean muscle tissue appeared protective, especially in men.
Interestingly, the researchers found differences between men and women. In women, muscle mass remained fairly stable until around ages 40 to 50 before declining more rapidly. Researchers believe hormonal changes during menopause and lower estrogen levels may partly explain this difference.
The study also found that people with low physical activity levels tended to have more hidden muscle fat and less healthy muscle tissue. This suggests that regular exercise may help prevent harmful changes inside muscles.
Dr. Ziegelmayer explained that the findings could help create new imaging-based biomarkers in the future. Biomarkers are measurable signs inside the body that help doctors estimate disease risk.
Because MRI scans are already widely used in hospitals, doctors may eventually use scans performed for other reasons to also evaluate hidden cardiometabolic risk.
For example, someone receiving an MRI for back pain might also receive information about hidden muscle fat and possible future risks for diabetes or heart disease.
Researchers believe this approach may help identify people who appear healthy during routine medical exams but actually face increased risk of future disease.
The study also highlights how artificial intelligence is rapidly changing medicine. Computer models can now analyze medical scans in ways that were previously impossible or extremely time-consuming.
Still, the researchers say more studies are needed before muscle-fat analysis becomes part of standard medical care. The study only showed associations between hidden fat and disease risk, not direct proof that one causes the other.
Even so, the findings provide strong evidence that muscle quality may be just as important as body weight when evaluating long-term health.
In the future, doctors may look beyond simple weight measurements and focus more closely on how fat and muscle are distributed throughout the body.
The research findings were published in the journal Radiology.
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