Muscle fat can increase mortality risk as much as type 2 diabetes

• Experts say they aren’t sure why fat accumulates in muscles as people age.
• Researchers now report that muscle fat can raise the risk of death as much as type 2 diabetes and smoking.
• They urge medical professionals to use methods other than body-mass index to calculate muscle fat.

High levels of fat often lurk as a silent killer deep within muscles.

The accumulation of fat in skeletal muscles, known as myosteatosis, can, in fact, raise the risk of death among otherwise healthy adults as much as type 2 diabetes and smoking, according to a new study published in the journal Radiology.

While a growing body of research identifies serious health dangers associated with myosteatosis, the researchers said, it often goes overlooked by physicians, who often estimate body fat by relying body mass index (BMI) to estimate body fat.

The researchers said, BMI fails to provide an accurate representation of body composition because people with similar BMIs can have widely varying levels of health risks.

They said abdominal CT or MRI scans provide a more accurate and thorough assessment of fat accumulations. The study authors suggest that should prompt the medical community to rethink standards on assessing the health risks of muscle fat.

Details from the muscle fat study

During the study, researchers tracked adverse health events such as heart attacks, strokes, and aneurysms during a follow-up period of about 9 years.

Of nearly 9,000 healthy adults in the study, 507 died during the follow-up period and myosteatosis increased the risk of major adverse events and appeared in 55% of those who died.

The researchers reported that excess muscle fat increased the absolute mortality rate at 10 years by 15%, more than for known risk factors for early death such as obesity (7%), fatty liver disease (8%) and muscle wasting (9%).

“Such a high death rate because of the elevated fat levels in muscles is really important and I think that when people hear that this can kill them, it will really wake them up, really get their attention,” said Dr. Steven Heymsfield, a professor of metabolism and body composition with Louisiana State University’s Pennington Biomedical Research Center who was not involved in the study.

The role of artificial intelligence in the research

Artificial intelligence (AI) played a major role in enabling researchers to extract body-composition metrics from abdominal CT scans on asymptomatic adults who had undergone a routine screening for colorectal cancer between 2004 and 2016.

Heymsfield told Medical News Today that the use of AI in the study reflects its growing role in modern medicine through its ability to analyze voluminous amounts of data quickly.

“AI is really taking us into a whole new world,” he said. “One of the most significant developments in medicine at the moment is AI. It’s just revolutionizing medicine in a really transformative way.”

Age not a factor

Dr. Maxime Nachit, a study co-author and a post-doctoral researcher at the Institute for Experimental and Clinical Research UCLouvain in Belgium, said the link between myosteatosis and higher risk of death was unrelated to age or obesity markers revealed by BMI.

“In other words, this means that fat accumulation in the muscles is not merely explained by being older and/or having fat overload in other locations of the body,” Nachit told Medical News Today.

He said future studies could help determine whether myosteatosis is solely a biomarker of poorer health status or whether it is causally associated with an increased risk of death.

The mystery of muscle fat

Accumulation of fat in muscles increases with age and as muscles atrophy, but precisely why is not fully clear, experts say, but they add that genetics may partly explain it.

Exercise can help reduce muscle fat among those at risk of becoming obese, according to a 2021 study in the Journal of Applied Physiology.

Previous research has linked muscle fat to health risks.

A 2022 study in the journal JACC: Heart Failure, for example, reported that high levels of intramuscular fat infiltration increased the risk of heart failure.

In addition, a 2019 study in the Journal of Epidemiology & Community Health revealed that the amount of lean muscle a healthy person has in middle age is linked to their future risk of heart disease.

Other studies have drawn a link between fatty muscles and poor outcomes.

For example, a 2020 study in the journal Critical Reviews in Oncology/Hematology found that cancer patients diagnosed with myosteatosis had a 75% greater mortality risk than those without fatty muscles.

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