Is invisible fat hiding in your muscles? Here’s how it may be affecting your heart—no matter your size
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Disclaimer: The information provided in this article is for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always consult your physician or other qualified healthcare providers with any questions you may have regarding a medical condition or before making any changes to your health regimen.
When we think about fat and health, we often picture visible weight gain or the type that affects heart health.
But what if there was a hidden type of fat—one you can’t see or feel—that could be silently affecting your heart and overall health?
This type of fat, called intermuscular fat, weaves itself between muscle fibers, much like the marbling in a steak.
While that might make a good cut of meat more tender, in the human body, it’s far less appealing.
In fact, research suggests it could increase the risk of heart disease—even in people who appear to be a healthy weight.
Intermuscular fat builds up between and within muscle fibers.
Unlike subcutaneous fat, which sits just beneath the skin, this hidden fat is stored deep in the muscles, making it impossible to detect without specialized imaging.
Researchers from Brigham and Women’s Hospital and Harvard Medical School recently found that higher levels of this muscle fat are strongly linked to heart disease.
Their study, published in the European Heart Journal, examined 669 people with chest pain or shortness of breath but no obvious artery blockages.
The results were eye-opening—those with more fat in their muscles were significantly more likely to experience heart damage or even life-threatening complications.
For every 1% increase in muscle fat, the risk of damage to the heart’s small blood vessels rose by 2%, while the likelihood of developing heart disease jumped by 7%.
Unlike fat that simply adds extra padding, intermuscular fat is metabolically active.
It doesn’t just sit there—it releases inflammatory chemicals that interfere with how the body processes glucose (sugar).
Over time, this can lead to insulin resistance, raising blood sugar levels and increasing the risk of type 2 diabetes.
It also contributes to plaque buildup in arteries, a leading cause of heart attacks and strokes.
Professor Viviany Taqueti, who led the Harvard study, explains, "Fat stored under the skin is quite benign and doesn’t seem to do much.
But fat around or inside organs—including muscles—is much more active. It can secrete hormones and chemical messengers that impact how well the body uses energy."
One of the most surprising findings from the research is that intermuscular fat doesn’t always correlate with body weight or BMI (Body Mass Index).
Two people with the same BMI could have vastly different levels of muscle fat—and very different health risks.
"Some people had less than 5% fat in their muscles, while others with the same BMI had over 25%," says Professor Taqueti. "You couldn’t tell just by looking at them."
This challenges the idea that BMI alone is a reliable measure of health and suggests that even those who appear to be at a healthy weight could still be at risk.
As we age, we naturally lose muscle mass—a process known as sarcopenia.
At the same time, fat tends to accumulate inside the muscles, especially if we’re not staying active.
This can lead to reduced strength, mobility issues, and a higher risk of falls.
Professor Francis Stephens, an expert in exercise metabolism at the University of Exeter, explains, "Fat in muscles appears to impair their ability to contract. It also disrupts how insulin works, making it harder for muscles to absorb glucose from the blood."
In other words, fatty muscles don’t just affect appearance—they can impact energy levels, strength, and heart health.
Currently, there’s no simple test at your doctor’s office to check for intermuscular fat.
Detecting it requires advanced imaging like CT or MRI scans, which are typically used for research or specific medical evaluations.
But the good news is, you don’t need a scan to start taking action.
The best part? Intermuscular fat isn’t permanent. Just like belly fat, it can be reduced—and even reversed—with the right lifestyle changes. Here’s what experts recommend:
Whether you’re slim, overweight, or somewhere in between, keeping your muscles strong and active is one of the best things you can do for your heart, metabolism, and longevity.
So, the next time you consider skipping a workout, remember—it’s not just about appearance. It’s about keeping your muscles lean, your heart healthy, and your body functioning at its best.
Read next: Save your life in 5 minutes? Try this simple at-home test a leading cardiologist swears by!
Have you noticed changes in your strength or energy levels as you’ve aged? Do you have a favorite way to stay active? We’d love to hear your thoughts and tips in the comments below!
When we think about fat and health, we often picture visible weight gain or the type that affects heart health.
But what if there was a hidden type of fat—one you can’t see or feel—that could be silently affecting your heart and overall health?
This type of fat, called intermuscular fat, weaves itself between muscle fibers, much like the marbling in a steak.
While that might make a good cut of meat more tender, in the human body, it’s far less appealing.
In fact, research suggests it could increase the risk of heart disease—even in people who appear to be a healthy weight.
Just like the marbling in bacon, intermuscular fat weaves through muscles—but in the body, it’s far less appetizing and could impact heart health. Image Source: Pexels / Nicolas Postiglioni.
What is intermuscular fat?
Intermuscular fat builds up between and within muscle fibers.
Unlike subcutaneous fat, which sits just beneath the skin, this hidden fat is stored deep in the muscles, making it impossible to detect without specialized imaging.
Researchers from Brigham and Women’s Hospital and Harvard Medical School recently found that higher levels of this muscle fat are strongly linked to heart disease.
Their study, published in the European Heart Journal, examined 669 people with chest pain or shortness of breath but no obvious artery blockages.
The results were eye-opening—those with more fat in their muscles were significantly more likely to experience heart damage or even life-threatening complications.
For every 1% increase in muscle fat, the risk of damage to the heart’s small blood vessels rose by 2%, while the likelihood of developing heart disease jumped by 7%.
Also read: Transform your health instantly: Replace butter with this fat and reduce your health risks!
Why is this fat so dangerous?
Unlike fat that simply adds extra padding, intermuscular fat is metabolically active.
It doesn’t just sit there—it releases inflammatory chemicals that interfere with how the body processes glucose (sugar).
Over time, this can lead to insulin resistance, raising blood sugar levels and increasing the risk of type 2 diabetes.
It also contributes to plaque buildup in arteries, a leading cause of heart attacks and strokes.
Professor Viviany Taqueti, who led the Harvard study, explains, "Fat stored under the skin is quite benign and doesn’t seem to do much.
But fat around or inside organs—including muscles—is much more active. It can secrete hormones and chemical messengers that impact how well the body uses energy."
Also read: Warning: What your feet reveal about your heart health
You can’t judge a book by its cover—or a body by its BMI
One of the most surprising findings from the research is that intermuscular fat doesn’t always correlate with body weight or BMI (Body Mass Index).
Two people with the same BMI could have vastly different levels of muscle fat—and very different health risks.
"Some people had less than 5% fat in their muscles, while others with the same BMI had over 25%," says Professor Taqueti. "You couldn’t tell just by looking at them."
This challenges the idea that BMI alone is a reliable measure of health and suggests that even those who appear to be at a healthy weight could still be at risk.
Also read: Is your daily sitting canceling out your exercise efforts? Avoid the hidden risks of too much sitting!
How muscle fat changes with age
As we age, we naturally lose muscle mass—a process known as sarcopenia.
At the same time, fat tends to accumulate inside the muscles, especially if we’re not staying active.
This can lead to reduced strength, mobility issues, and a higher risk of falls.
Professor Francis Stephens, an expert in exercise metabolism at the University of Exeter, explains, "Fat in muscles appears to impair their ability to contract. It also disrupts how insulin works, making it harder for muscles to absorb glucose from the blood."
In other words, fatty muscles don’t just affect appearance—they can impact energy levels, strength, and heart health.
Can you measure your muscle fat?
Currently, there’s no simple test at your doctor’s office to check for intermuscular fat.
Detecting it requires advanced imaging like CT or MRI scans, which are typically used for research or specific medical evaluations.
But the good news is, you don’t need a scan to start taking action.
Also read: Unlock the secret health benefits of NEAT in your daily routine
How to reduce muscle fat and protect your heart
The best part? Intermuscular fat isn’t permanent. Just like belly fat, it can be reduced—and even reversed—with the right lifestyle changes. Here’s what experts recommend:
- Get moving consistently – Aerobic and resistance exercises help reduce muscle fat.
- Maintain a healthy weight – Even small weight loss can lower intermuscular fat.
- Focus on an anti-inflammatory diet – Eat whole foods, lean proteins, and healthy fats while avoiding processed foods and sugary drinks.
- Be mindful of weight-loss medications – Ongoing research is studying their effect on muscle fat.
- Keep muscles strong with age – Strength training helps maintain muscle mass and overall health.
Whether you’re slim, overweight, or somewhere in between, keeping your muscles strong and active is one of the best things you can do for your heart, metabolism, and longevity.
So, the next time you consider skipping a workout, remember—it’s not just about appearance. It’s about keeping your muscles lean, your heart healthy, and your body functioning at its best.
Read next: Save your life in 5 minutes? Try this simple at-home test a leading cardiologist swears by!
Have you noticed changes in your strength or energy levels as you’ve aged? Do you have a favorite way to stay active? We’d love to hear your thoughts and tips in the comments below!
