Fat hidden within muscles that resembes the so-called marbling seen in beef significantly increases the risk of death from heart attacks or heart failure, regardless of a person’s body weight, a recent study has found.
While “fatty marbling” is prized in livestock for its commercial value, in humans, it has been linked to insulin resistance and type 2 diabetes, researchers noted.
Currently, there is no clear understanding on how to reduce the heart health risks associated with fatty muscles. However, experts believe these findings could prove valuable in ongoing research into how weight loss drugs affect heart health, BristolLive reported.
For their study, researchers in the US examined 669 individuals at Boston’s Brigham and Women’s Hospital. These patients, who were experiencing chest pain or shortness of breath, were found to have no signs of obstructive coronary artery disease, a condition caused by clogged arteries supplying the heart.
The study participants underwent heart function scans, with researchers also using CT scans to evaluate their body composition. These scans provided detailed measurements of fat and muscle distribution across different sections of their torso.
To assess the fat stored within muscles, the team calculated the ratio of intermuscular fat to the total muscle and fat, a measurement they referred to as the fatty muscle fraction.
Harvard Medical School Professor Viviany Taqueti, also director of the cardiac stress laboratory at Brigham and Women’s Hospital, said: “Intermuscular fat can be found in most muscles in the body, but the amount of fat can vary widely between different people.
“In our research, we analyse muscle and different types of fat to understand how body composition can influence the small blood vessels or ‘microcirculation’ of the heart, as well as future risk of heart failure, heart attack and death.”
Higher levels of fat in the muscles are linked to an increased risk of coronary microvascular dysfunction (CMD), a condition affecting the small blood vessels in the heart, and higher chances of hospitalisation or death due to heart disease.
The study showed that for every 1 per cent rise in fatty muscle fraction, the risk of CMD increased by 2 per cent and the risk of serious heart disease rose by 7 per cent. Researchers, including Prof Taqueti, noted that fat stored in muscles may contribute to inflammation and insulin resistance, unlike fat stored under the skin.
“In turn, these chronic insults can cause damage to blood vessels, including those that supply the heart, and the heart muscle itself,” she added.
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.”
Prof Taqueti said it is not yet known how to lower the risk for people with fatty muscles. “For example, we don’t know how treatments such as new weight-loss therapies affect fat in the muscles relative to fat elsewhere in the body, lean tissue, and ultimately the heart,” she added.
The findings, published in the European Heart Journal, could be “particularly important” for ongoing research into the “heart health effects of fat and muscle-modifying incretin-based therapies”, such as weight loss injections, she said.
Researchers suggest that glucagon-like peptide-1 receptor agonists, which promote the loss of lean muscle mass, might also lead to a reduction in intermuscular fat.
Prof Taqueti added: “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. This is especially true in women, where high body mass index may reflect more ‘benign’ types of fat.”
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