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New Study Links Intermuscular Fat to Increased Heart Disease Risk

Research published in the European Heart Journal reveals that individuals with pockets of fat within their muscles face a heightened risk of dying from heart-related issues, including heart attacks and heart failure, irrespective of their body mass index (BMI).

While intermuscular fat is often sought after for its culinary qualities in beef, its implications for human health remain underexplored. This study marks the first thorough investigation into how fatty deposits in muscles may influence heart disease outcomes.

The findings underscore the inadequacy of traditional metrics such as BMI or waist circumference in accurately assessing heart disease risk for all individuals, leading researchers to advocate for a more nuanced approach to cardiovascular risk evaluation.

Research Methodology

The research was spearheaded by Professor Viviany Taqueti, who directs the Cardiac Stress Laboratory at Brigham and Women’s Hospital, a subsidiary of Harvard Medical School in Boston. Professor Taqueti expressed concerns over the reliance on BMI, stating, “Obesity is among the most significant global challenges to cardiovascular health. Yet, BMI—our primary measure for categorizing obesity—is fraught with controversy and can misrepresent cardiovascular risk, particularly for women, where higher BMI may signify less harmful fat types.”

Intermuscular fat can accumulate in various muscle groups across individuals, with significant variability in fat deposition. The research team analyzed how this fat affects heart microcirculation and assessed the risk of future heart complications.

Study Population and Findings

The study involved 669 patients referred to Brigham and Women’s Hospital due to chest pain or shortness of breath but without signs of obstructive coronary artery disease. The participants had an average age of 63, predominantly female (70%) and nearly half identified as non-white.

To gauge heart function, each participant underwent cardiac positron emission tomography/computed tomography (PET/CT) scanning. In addition, CT scans were used to evaluate body composition, focusing on the distribution of fat and muscle in their torsos.

Researchers introduced a metric termed the fatty muscle fraction, calculated as the ratio of intermuscular fat to total muscle and fat, to quantify fat accumulation within muscles. Participants were monitored for approximately six years, during which researchers documented instances of mortality and hospitalizations related to heart attacks or heart failure.

The study established a correlation between higher intermuscular fat levels and damage to coronary microvessels (coronary microvascular dysfunction or CMD), which significantly raised the likelihood of hospitalization or death from heart disease. Specifically, a 1% increase in the fatty muscle fraction corresponded to a 2% increase in CMD risk and a staggering 7% rise in serious cardiovascular issues, independent of BMI and other risk factors.

Notably, patients with both high intermuscular fat and signs of CMD exhibited the greatest risk of adverse outcomes, while those with greater lean muscle mass showed lower heart disease risk. It is essential to note that fat located beneath the skin (subcutaneous fat) was not linked to increased risk.

Implications and Future Directions

Professor Taqueti remarked, “Intermuscular fat may drive inflammation and alter glucose metabolism, contributing to insulin resistance and metabolic syndrome, which, in turn, harm blood vessels, including those feeding the heart and the heart muscle itself.”

Recognizing the role of intermuscular fat in heart disease risk could refine risk stratification and patient identification beyond BMI metrics. This could have significant implications for assessing the effects of weight-loss therapies, particularly those that modify muscle and fat composition.

As the research team continues to investigate treatment strategies—encompassing exercise, dietary interventions, and weight-loss therapies—the quest to understand how best to mitigate risks linked to fatty muscle deposits remains a priority.

An editorial accompanying the study, authored by Dr. Ranil de Silva from Imperial College London, reiterated the complexity of the obesity-cardiovascular health relationship and highlighted that elevated levels of intermuscular fat are linked to an increased occurrence of CMD independent of BMI.

Dr. de Silva emphasized the need for closer scrutiny of current data and suggested that additional research should aim to clarify the underlying mechanisms connecting elevated intermuscular adipose tissue with cardiovascular risks. He called for further studies to assess how markers of fat distribution can enhance traditional methods for stratifying cardiac risk in patients.

Source
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