Excess fat hidden in and around muscles increases the risk of heart disease. It also increases the risk of hospitalization. This is true even for people with a normal body mass index (BMI), according to a new study. Researchers discovered that intermuscular fat is a key predictor of cardiovascular disease. This finding reveals the limitations of BMI as a health marker.
“Intermuscular fat raises heart disease risk regardless of BMI, giving us a new way to identify high-risk individuals,” says Dr. Viviany Taqueti, director of the Cardiac Stress Laboratory at Brigham and Women’s Hospital.
Scientists have long linked fatty muscle to insulin resistance and type 2 diabetes. But, this study is the most comprehensive investigation into its impact on heart health. The findings suggest a crucial connection that may redefine how doctors assess cardiovascular risk.
BMI ALONE IS AN INADEQUATE MEASURE OF HEALTH
BMI is widely used to assess obesity-related risks, but experts argue that it oversimplifies the complexities of body fat distribution.
“Obesity is one of the biggest global threats to heart health. Yet, BMI remains a controversial and flawed marker,” says Taqueti. “This is especially true for women, as BMI may show different fat types with varying health impacts.”
INTERMUSCULAR FAT: THE HIDDEN CULPRIT
While body fat is essential, some types pose greater risks than others. Intermuscular adipose tissue (IMAT), which accumulates between muscle fibers, varies among individuals and increases with age. In some people, excessive IMAT leads to a condition called myosteatosis, contributing to mobility issues and metabolic disorders.
Earlier studies linked high IMAT levels to insulin resistance, but little was known about its cardiovascular effects. The new research changes that.
STUDY FINDINGS: FATTY MUSCLE AND HEART DISEASE RISK
Researchers analyzed 669 patients from Brigham and Women’s Hospital. These patients experienced chest pain or shortness of breath but had no obstructive coronary artery disease.
Key Study Insights:
- 70% of participants were women, 46% were non-white, with an average age of 63.
- PET/CT scans measured heart function, while CT scans analyzed fat and muscle composition.
- Follow-ups over six years tracked deaths and hospitalizations from heart-related events.
Patients with higher IMAT levels had a significantly greater risk of coronary microvascular dysfunction (CMD), heart failure, and heart attacks.
FATTY MUSCLE FRACTION: A CRITICAL MEASUREMENT
The researchers introduced a key metric: the fatty muscle fraction, or the ratio of intermuscular fat to total skeletal muscle and fat.
Key Findings:
- Every 1% increase in fatty muscle fraction raised CMD risk by 2%.
- It also increased the likelihood of major heart events by 7%, independent of BMI and other risk factors.
- Patients with both excess IMAT and CMD faced the highest risk of heart failure and death.
- Lean muscle mass was linked to lower cardiovascular risk.
WHY INTERMUSCULAR FAT IS DANGEROUS
Unlike subcutaneous fat, which sits beneath the skin, intermuscular fat contributes to inflammation, disrupts glucose metabolism, and promotes insulin resistance. Over time, this chronic stress damages blood vessels, including those supplying the heart.
“Fat stored in muscles may contribute to metabolic syndrome, leading to vascular damage and heart muscle dysfunction,” Taqueti explains.
STUDY LIMITATIONS AND FUTURE RESEARCH
The study provides crucial insights, but it has limitations. The authors call for further research to:
- Explore the mechanisms linking intermuscular fat and cardiovascular disease.
- Determine the best ways to measure and address fatty muscle fraction.
- Develop targeted interventions to reduce heart disease risk in affected individuals.
THE FUTURE OF HEART DISEASE PREVENTION
These findings highlight the need for a broader approach to heart health assessment beyond BMI. Measuring intermuscular fat could help identify high-risk individuals earlier, leading to better prevention and treatment strategies.
“Understanding how fat affects the heart could save lives,” Taqueti emphasizes. “It’s time to rethink how we assess and mitigate cardiovascular risk.”
As research progresses, doctors may soon incorporate fatty muscle fraction into routine health screenings. It offers a more precise measure of heart disease risk and helping patients take proactive steps toward heart health.
