Can Fat Be Benign? A New Study Reexamines the Relationship Between Muscle, Body Fat, and Heart Disease

The Limitations of BMI as a Health Measurement Tool

In recent years, the BMI (Body Mass Index) tool has been treated with skepticism by many health and fitness experts. There are many issues with the BMI standard (which you can read about here), but one of them is its failure to take into account muscle and fat content.

Someone can technically be in the ‘overweight’ range but have a high percentage of lean muscle mass, which is denser and heavier than fat. On the other end, another individual can be in the ‘normal’ range for their weight, but lack a sufficient amount of muscle tissue, be at risk for heart disease, and even be pre-diabetic or diabetic.

More and more, we are coming to recognize the essential role that muscle plays in our health. Recently, some experts have been arguing that the ‘obesity epidemic’ should actually be reframed as a ‘sarcopenia epidemic’, claiming that more significant markers for health are lean muscle mass, and the type and location of body fat, especially in women. 

The New Study: Rethinking BMI and Heart Disease

A recent study has further complicated the relationship between BMI, body fat, and cardiovascular health. The study’s authors argue that while BMI is a popular tool for measuring obesity, it is “a controversial and flawed marker of cardiovascular prognosis,” especially in women. The researchers suggest that high BMI in women may reflect more “benign” types of fat that aren’t as harmful to heart health as previously thought.

Study Design and Methodology

The study followed 669 individuals—70% of whom were women—for six years. Researchers used a variety of medical tools, including EKG machines and CT scanners, to assess heart function and analyze the type and location of body fat in each participant. They tracked whether individuals had been hospitalized for heart attacks or heart failure, or whether they had died during the study period.

Key Findings: Intramuscular Fat and Heart Disease Risk

The study’s findings shed new light on the impact of different types of body fat:

1. Intramuscular Fat and Heart Health

• Individuals with higher amounts of fat stored in their muscles were more likely to develop coronary microvascular dysfunction (CMD)—a condition affecting the tiny blood vessels that supply the heart.
• These individuals were also at higher risk for heart disease, hospitalization, and even death.
• Even a small increase in intramuscular fat was associated with a heightened risk for heart disease, regardless of other known risk factors like BMI.

2. Lean Muscle Mass and Cardiovascular Protection

• Those with higher amounts of lean muscle mass were found to be at a lower risk for death, heart disease, and heart failure.
• Subcutaneous fat (the fat just under the skin) had little to no correlation with heart function, suggesting that not all fat is created equal.

What Does This Mean for You?

While this new research challenges some long-held assumptions about body fat, it’s important to keep in mind that scientific studies are ongoing. We are only beginning to understand how muscle and fat interact in the body. In a previous Infofit article, we discussed a different study and its hypothesis that a diet high in ultra-processed food will result in higher intramuscular fat content.

While it’s unlikely that BMI will be discarded as a health measurement tool anytime soon, it’s clear that we should approach its results with more skepticism. The growing focus on lean muscle mass and intramuscular fat highlights the need for more accurate ways to assess our health and fitness.

What Should We Use Instead of BMI?

There are alternative methods for assessing body composition that may provide a more complete picture of our health and fitness levels:

1. Skinfold Tests

• Measures subcutaneous fat using calipers.
• Commonly used in fitness assessments.
• Inexpensive and widely accessible.

2. Bioelectrical Impedance Analysis (BIA)

• Commonly known as InBody scanners.
• Measures body fat percentage, muscle mass, and water content.
• More accurate than BMI, but still has limitations.

3. Advanced Imaging Techniques

• CT scans and MRI can measure intramuscular fat but are not readily available for everyday fitness assessments.
• Best used for clinical research and medical diagnostics.

The Bottom Line: Focus on Building Lean Muscle

While we are still in the early stages of understanding how intramuscular fat affects heart health, one thing is clear: maintaining lean muscle mass is essential for cardiovascular health.

Actionable Steps to Improve Heart Health:

• Incorporate resistance training to build and maintain muscle mass.
• Reduce consumption of ultra-processed foods, which have been linked to higher intramuscular fat content.
• Prioritize high-protein diets to support muscle growth and maintenance.
• Use multiple health assessment tools (such as BIA and skinfold tests) rather than relying solely on BMI.

While BMI might still be a part of the conversation, make sure you’re also focusing on strength training, body composition, and overall metabolic health.

Your heart will thank you!

Wishing you all the best on your journey to optimum health!

Written by Theresa Faulder, Master’s in English, Certified Personal Trainer, and Infofit Fitness Blog Writer.

Works Cited

European Society of Cardiology. (2025, January 19). Fatty muscles raise the risk of serious heart disease regardless of overall body weight. ScienceDaily. Retrieved January 26, 2025

Ana Carolina do A H Souza, Amelie S Troschel, Jan P Marquardt, Ibrahim Hadžić, Borek Foldyna, Filipe A Moura, Jon Hainer, Sanjay Divakaran, Ron Blankstein, Sharmila Dorbala, Marcelo F Di Carli, Hugo J W L Aerts, Michael T Lu, Florian J Fintelmann, Viviany R Taqueti. Skeletal muscle adiposity, coronary microvascular dysfunction, and adverse cardiovascular outcomes. European Heart Journal, 2025; DOI: 10.1093/eurheartj/ehae827