Revealing the Hidden Threat: Intermuscular Fat’s Role in Heart Disease Beyond BMI

In a telling revelation, the European Society of Cardiology (ESC) has spotlighted a stealthy adversary lurking in our muscles — intermuscular fat. This obscure deposit is now identified as an insidious risk factor for heart disease, independent of the ubiquitous Body Mass Index (BMI). Contrary to the allure it holds in culinary delights like beef steaks, intermuscular fat marks its presence as a harbinger of health concerns, setting the stage for cardiovascular calamities such as heart failure and attacks.

The research, published in the European Heart Journal, unravels the complexity of our body’s fat composition — a complexity that BMI fails to capture. Professor Viviany Taqueti, leading the study at Harvard’s Brigham and Women’s Hospital, underscores this very point. She elucidates, “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.”

Intriguingly, the study’s cohort of 669 individuals, predominantly female and racially diverse, offered a fertile ground for examination. These patients, all evaluated for chest discomfort sans coronary artery obstruction, underwent sophisticated PET/CT scanning. The scans enabled researchers to map the intricacies of fat and muscle distribution in their bodies, quantifying the elusive fatty muscle fraction. This metric became the linchpin, revealing a troubling connection — a 1% hike in this fraction catapulted individual risk for coronary microvascular dysfunction (CMD) by 2% and heightened the potential for severe heart disease by 7%.

Professor Taqueti’s insights drive home a stark reality — “People who had high levels of intermuscular fat and evidence of CMD were at an especially high risk of death, heart attack and heart failure. In contrast, people with higher amounts of lean muscle had a lower risk.” The study delineates an insidious cascade where intermuscular fat possibly incites inflammation, metabolic disarray, and insulin resistance, all of which contribute to vascular damage.

The potential of these findings reverberates beyond academia. They offer a clarion call to re-evaluate our understanding of adiposity and heart health, especially in an era marked by the advent of fat and muscle-modifying incretin therapies. Yet, as Taqueti cautions, “What we don’t know yet is how we can 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.”

The research beckons further exploration, posing more questions than it answers, as noted in the accompanying editorial by Dr. Ranil de Silva and colleagues from Imperial College London. They resonate with the sentiments that the findings are “hypothesis generating” and urge integration of adiposity markers into conventional and budding cardiac risk stratification frameworks.

The narrative of intermuscular fat, it appears, is not just about layers of hidden lipids but a deeper story of human health — one that interconnects fat, muscle, and life’s most vital organ, the heart.