Most people know that body fat stored around the midsection can spell disaster for cardiovascular health. But Harvard researchers have now discovered another problematic fat-storage location in the body that's been largely overlooked.
A team led by Viviany Taqueti, director of the Cardiac Stress Laboratory at Harvard's Brigham and Women's Hospital, looked at 669 people who were admitted to the hospital for chest pain and/or shortness of breath despite showing no signs of obstructive coronary artery disease, a condition in which the arteries feeding into the heart become seriously clogged. Seventy percent of the people studied were female, there was a roughly even split between white and non-white participants, and the average age of the group was 63.
At the time of admission, the patients had their hearts examined by PET/CT scans. They also had their body composition analyzed using CT scans. The researchers then calculated each patient's "fatty muscle fraction," which is a measurement of fat inside their muscles to their total body fat.
After six years, the researchers followed up with the patients. They found that for every 1% increase in intramuscular fat, people had a 2% higher risk of suffering from coronary microvascular dysfunction (CMD), a condition wherein the small blood vessels that serve the heart are damaged. Furthermore, every 1% increase in muscle-based fat led to a 7% increased risk of developing future serious heart-disease risk. These findings were independent of someone's total fat, measured in terms of their body mass index, or BMI.
“Compared to subcutaneous fat, fat stored in muscles may be contributing to inflammation and altered glucose metabolism leading to insulin resistance and metabolic syndrome," said Taqueti. "In turn, these chronic insults can cause damage to blood vessels, including those that supply the heart, and the heart muscle itself."
Taqueti says that while fat under the skin is easy to see, the new finding about fat stored in muscles raises questions about how to evaluate someone's risk of developing heart disease, as we all store fat in our muscles at different rates. Looking at BMI alone, a tool that compares height to weight to derive total body fat, might no longer be enough.
“Knowing that intermuscular fat raises the risk of heart disease gives us another way to identify people who are at high risk, regardless of their body mass index," Taqueti says. "These findings could be particularly important for understanding the heart health effects of fat and muscle-modifying incretin-based therapies, including the new class of glucagon-like peptide-1 receptor agonists." This drug class includes the widely popular semaglutide, marketed as Ozempic, which was shown in three studies a few months ago to boost heart health.
Taqueti says her team hasn't figured out how to lower the risk for people with fatty muscles, but it's now looking at ways in which fat-fighting strategies like diet, exercise, surgery and weight-loss drugs might impact body composition and the rates of heart disease.
The results of the study have been published in the European Heart Journal.
Source: European Society of Cardiology
