The Hidden Fat in Your Body That Could Be Killing You

Dangerous Kind of Fat Hidden in the Body Can Raise Your Risk of Death

While body fat has long been linked to an array of health issues, there’s a particular kind of fat that’s hidden within your muscles that may pose an even greater risk to your health—one that might go unnoticed in routine assessments. Recent studies have revealed that excess fat accumulating around and within skeletal muscle, known as intermuscular adipose tissue (IMAT), could substantially increase the risk of heart disease, hospitalization, and even death—an association that persists even in individuals with a normal body mass index (BMI). What makes this fat so dangerous, and why has it remained relatively under the radar in the medical field?

In this article, we’ll dive into the latest research on intermuscular fat, how it impacts cardiovascular health, and why it’s time to reconsider traditional metrics like BMI when assessing an individual's risk of heart disease.

What Is Intermuscular Adipose Tissue (IMAT)?

To understand why intermuscular fat is a hidden danger, it’s important to first grasp what intermuscular adipose tissue (IMAT) is. IMAT refers to fat deposits that are embedded between muscle fibers. While body fat typically accumulates under the skin (subcutaneous fat) or around internal organs (visceral fat), intermuscular fat is the fat that infiltrates the muscles themselves. It’s natural to have small amounts of intermuscular fat; it even plays a role in providing energy and cushioning to muscles. However, when too much fat accumulates in this space, it leads to a condition known as myosteatosis, or fatty muscle infiltration.

As individuals age or experience changes in metabolism, the amount of intermuscular fat can increase. This process can contribute to a host of health issues, especially when accompanied by other conditions like insulin resistance and type 2 diabetes. What's troubling is that this fat is not easily detected in routine health exams, and it doesn't always correlate with traditional body fat measurements like BMI.

How Does IMAT Affect Your Heart?

In recent years, researchers have begun investigating the effects of intermuscular fat on cardiovascular health, and the results are concerning. A study published in 2020 shed light on the dangerous link between fatty muscle and coronary microvascular dysfunction (CMD)—a condition in which the tiny blood vessels that supply the heart become damaged. These damaged microvessels are associated with higher risks of heart disease, heart failure, and other major cardiovascular events.

The study found that individuals with higher levels of intermuscular fat had an increased risk of CMD, heart attack, and heart failure, regardless of their BMI or other traditional risk factors. Specifically, every 1% increase in the fatty muscle fraction—a measure that quantifies the amount of fat relative to muscle—was associated with a 2% higher risk of CMD and a 7% higher risk of major cardiovascular events like heart attack or heart failure.

The link between intermuscular fat and heart disease is not entirely understood, but the data suggests that this fat may contribute to inflammation, altered glucose metabolism, and insulin resistance—factors that can damage blood vessels and lead to cardiovascular problems. Unlike subcutaneous fat, which lies just beneath the skin and is often seen as "less dangerous," fat stored within muscles appears to disrupt normal metabolic processes in a more harmful way.

The Role of BMI in Assessing heart disease Risk

As heart disease continues to be one of the leading causes of death worldwide, clinicians have traditionally relied on BMI (Body Mass Index) as a key indicator of whether someone is at risk. However, BMI, which is calculated based on height and weight, has limitations. It does not differentiate between lean mass (muscle) and fat mass, nor does it account for where fat is distributed within the body. This has led many experts to question its usefulness, especially when it comes to accurately predicting heart disease risk.

The study on IMAT is a prime example of why BMI alone is an insufficient marker for cardiovascular health. While BMI may suggest a "healthy" weight, it doesn't account for the hidden dangers of fat accumulating in muscles. As the research showed, individuals with a high fatty muscle fraction—even if their BMI is within a normal range—are still at a higher risk of heart disease, especially if they also show signs of coronary microvascular dysfunction. In fact, this study’s findings point to IMAT as a potential risk factor for heart disease that has largely been ignored in clinical assessments.

Furthermore, the researchers noted that women may face an even greater discrepancy. For women, BMI often doesn’t reflect the true health risks associated with fat distribution. As the study's co-author explained, high BMI in women may reflect "benign" types of fat, such as subcutaneous fat, which doesn't carry the same risks as visceral fat or fat in the muscles.

Study Details and Findings

The groundbreaking study in question involved 669 participants who were all patients at Brigham and Women’s Hospital. These patients experienced chest pain or shortness of breath but showed no signs of obstructive coronary artery disease (CAD). The study participants were monitored for a period of about six years, during which any heart-related hospitalizations or deaths were recorded.

To examine the relationship between fat accumulation and heart health, the researchers employed advanced imaging techniques like cardiac positron emission tomography (PET) and computed tomography (CT) scans. These scans provided detailed pictures of both the heart’s microcirculation and the distribution of fat and muscle within the body. By analyzing the fatty muscle fraction, the researchers were able to determine the proportion of fat relative to muscle and how this affected heart health.

The study revealed that individuals with high levels of IMAT were at a significantly higher risk of heart disease, even when controlling for other known risk factors like BMI, smoking, and blood pressure. Patients with elevated IMAT who also showed signs of CMD were particularly vulnerable, facing an even greater risk of death, heart attack, and heart failure.

Study Reference: https://academic.oup.com/eurheartj/...j/ehae827/7958241?login=false#google_vignette

The Biological Mechanism Behind IMAT and heart disease

What makes intermuscular fat so dangerous? While the exact mechanisms are still being explored, researchers have hypothesized that IMAT contributes to heart disease in a number of ways:

1. Chronic Inflammation: Fat cells, especially those within muscles, release inflammatory markers that can damage blood vessels over time. This inflammation may impair the function of the heart’s small blood vessels, contributing to conditions like coronary microvascular dysfunction (CMD).
2. Altered Glucose Metabolism: Excessive fat in muscles disrupts the body’s ability to process glucose properly, leading to insulin resistance. Insulin resistance is a key factor in the development of type 2 diabetes, and it is also strongly associated with heart disease. The presence of IMAT can exacerbate these metabolic issues, leading to further damage to the cardiovascular system.
3. Impaired Muscle Function: The presence of fat within muscles can interfere with normal muscle function, leading to muscle weakness and loss of strength. This can affect mobility and overall physical activity, making it harder for individuals to engage in the types of exercises that promote heart health.

The Importance of Addressing IMAT in Cardiovascular Risk Assessments

This study underscores the need for a broader approach to assessing cardiovascular risk—one that goes beyond traditional markers like BMI. As we’ve seen, intermuscular fat plays a significant role in heart disease, and individuals who are at risk may not show any outward signs in their BMI or weight alone.

The medical community now has an opportunity to refine cardiovascular risk assessments by considering the role of IMAT. By using more advanced imaging techniques and focusing on body composition, clinicians could identify individuals at risk for heart disease earlier, allowing for more targeted interventions. This approach could also help clinicians recommend lifestyle changes, such as diet and exercise, that are tailored to the specific needs of individuals based on their body composition.

Next Steps and Future Research

The study of intermuscular fat is still in its early stages, and much remains to be explored. Future research should continue to investigate the exact mechanisms by which IMAT contributes to heart disease and how it interacts with other risk factors. Additionally, studies are needed to better understand how to treat or reverse the effects of excessive intermuscular fat. As our understanding of this condition deepens, we may be able to develop more effective ways to prevent cardiovascular disease and improve overall health.

Conclusion: Rethinking heart disease Risk

The findings on intermuscular fat highlight the limitations of traditional metrics like BMI and call for a more nuanced approach to cardiovascular health. Intermuscular fat is a dangerous, often overlooked contributor to heart disease, and individuals with high levels of this fat are at an elevated risk of hospitalization and death from cardiovascular events.

By considering fat distribution as a risk factor, rather than relying solely on BMI, healthcare providers can better identify those at risk and implement more personalized strategies for prevention and treatment. Understanding the link between IMAT and heart disease opens the door to more effective interventions and could help save countless lives in the years to come.