Fat Within Muscles More Dangerous for Heart Than Overall Body Weight
Fat Within Muscles More Dangerous for Heart Than Overall Body Weight

By George Citroner

Hidden fat within your muscles could be a more substantial warning sign of heart disease than your overall weight, according to Harvard researchers.

They found that even a 1 percent increase in fatty muscle raises cardiovascular risk by 7 percent.

The new study challenges decades of reliance on body mass index (BMI) as the primary measure of obesity-related heart risks.

“Obesity is now one of the biggest global threats to cardiovascular health, yet body mass index—our main metric for defining obesity and thresholds for intervention—remains a controversial and flawed marker of cardiovascular prognosis,” lead researcher Viviany Taqueti, director of the Cardiac Stress Laboratory at Brigham and Women’s Hospital and a professor at Harvard Medical School, said in a press statement.

Muscle Fat Increased Disease Risk

The new research, published Monday in the European Heart Journal, indicates that fat stored between muscle fibers or muscle groups increases the risk of coronary microvascular dysfunction (CMD). This common heart condition occurs when the heart does not get enough blood supply due to problems in its smaller blood vessels.

Coronary microvascular dysfunction may affect about half of people without evidence of coronary artery obstruction, and women have a higher risk. Symptoms can include chest pain and shortness of breath.

“Intermuscular fat can be found in most muscles in the body, but the amount of fat can vary widely between different people,” Taqueti said in the press statement.

The study followed 669 people who underwent cardiac stress testing at Brigham and Women’s Hospital in Boston for six years.

The stress test involved injecting a small amount of radioactive tracer into the bloodstream. Next, a positron emission tomography (PET) scanner took images of participants’ hearts while at rest and then while under stress induced by a medication that dilates the coronary arteries.

“Increased intermuscular fat is associated with CMD and adverse cardiovascular outcomes independently of BMI and conventional risk factors,” the researchers wrote in the study.

BMI Didn’t Reveal Risk

The findings suggested that while BMI—often used as a measure of obesity—correlated with various fat metrics, it did not independently predict CMD. Instead, decreased skeletal muscle and increased fatty muscle remained independently associated with diminished coronary flow reserve.

The researchers also found that every 1 percent increase in fatty muscle (compared to lean muscle) was linked to a 2 percent higher chance of developing CMD and a 7 percent increased risk of adverse cardiovascular events.

​Furthermore, the researchers highlighted that patients with both CMD and high fatty muscle levels faced the highest risk of complications.

“Patients with both CMD and fatty muscle demonstrated the highest risk of events,” they wrote.​

At-Risk People May Be Overlooked

The authors emphasized evaluating not only overall body weight or fat but also the quality of skeletal muscle in assessing heart health.

They also noted that traditional measures like BMI may overlook at-risk individuals, particularly women and younger patients with higher subcutaneous fat located just under the skin but less fat around the abdominal organs.

“Compared to subcutaneous fat, fat stored in muscles may be contributing to inflammation and altered glucose metabolism leading to insulin resistance and metabolic syndrome,” Taqueti explained in the press release.

“In turn, these chronic insults can cause damage to blood vessels, including those that supply the heart, and the heart muscle itself.”


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