Body mass index (BMI) is a value many people keep an eye on, believing it to be a key indicator of their health and weight, yet this metric alone falls short of telling the whole story when it comes to your heart. Even if you have a “normal” BMI, thinking you’re in the clear, a danger could still be present within your body.
Deep within your muscles, unseen and unconsidered by simple weight measurements, resides a type of fat that poses a silent threat to your cardiovascular system. This “hidden” fat, scientifically referred to as intermuscular adipose tissue, or IMAT, quietly infiltrates your muscles and accumulates even if your BMI is in the healthy range. IMAT is not inert; it’s a metabolically active tissue that promotes inflammation and disrupts normal metabolic processes.
This infiltration of fat has a particularly damaging effect on the delicate network of small blood vessels in your heart, increasing the risk of major cardiovascular events like heart failure and myocardial infarction, or heart attack. This dangerous process often occurs without noticeable symptoms in its early stages, making IMAT a health hazard that often progresses undetected.
If elevated levels of IMAT are ignored, the consequences are steep, often culminating in coronary microvascular dysfunction, a serious condition that significantly elevates your likelihood of heart failure, heart attacks and even death. Now, research is bringing these silent dangers into the light, beginning with a pivotal study published in the European Heart Journal that uncovers the intricate link between muscle fat and microvascular issues in the heart.1
Muscle Fat Quantity Impacts Heart Function
Research published in the European Heart Journal revealed a concerning link between the fat content in your muscles and the well-being of your heart.2
This study sought to understand just how skeletal muscle fat, another term for IMAT, influences coronary microvascular function and subsequent cardiovascular health outcomes. The researchers aimed to determine if the quality of your muscles, specifically the amount of fat within them, plays a role in heart issues, independent of overall body weight.
To conduct this analysis, researchers employed advanced cardiac imaging on 669 individuals undergoing evaluations for coronary artery disease.
These patients, who had normal heart function and no major blockages in their arteries, were monitored for a median of six years. The study measured subcutaneous adipose tissue (SAT), skeletal muscle (SM) and IMAT in each participant. A clear and concerning pattern emerged: reduced skeletal muscle mass and elevated IMAT levels were directly associated with a decrease in coronary flow reserve (CFR).
Considering these results, it’s important to understand what CFR signifies: it’s a measure of how well your heart’s small blood vessels, known as microvasculature, are functioning.3 When CFR is diminished, it indicates coronary microvascular dysfunction (CMD), meaning these tiny vessels are not dilating and responding to stress as they should, which is important for delivering oxygen-rich blood to your heart muscle.
“Decreased SM and increased IMAT, but not BMI or SAT, remained independently associated with decreased CFR,” the study authors stated.4 Essentially, this means that the amount of fat nestled within your muscles is a key factor in the health of your heart’s microcirculation, regardless of your overall body weight or the fat just under your skin.
The implications extend further, as the study also established that both reduced CFR and elevated IMAT were independently linked to an increased risk of major adverse cardiovascular events (MACE).5
MACE is a composite endpoint that includes serious heart-related issues such as death, heart attack or heart failure. This highlights that the fat content in your muscle is not merely a bystander but an active contributor to cardiovascular risk, acting independently of what your BMI suggests.
For every single percentage point increase in what they termed “fatty muscle fraction” — the ratio of IMAT to total muscle tissue — individuals faced a 7% increased risk of experiencing major adverse cardiovascular events.6
The study also identified a particularly high-risk group: individuals who presented with both CMD and elevated IMAT. This combination of factors, CMD and fatty muscle, pinpoints a novel cardiometabolic risk profile that stands apart from conventional obesity measures or typical cardiovascular risk factors.
Ultimately, this research emphasizes that the quality of your skeletal muscle, specifically the amount of fat infiltrated within it, is tightly interwoven with the function of your coronary microvasculature and acts as a predictor of cardiovascular health, overshadowing the importance of BMI alone.
Lower Muscle Density Linked to Higher Death Risk in Aging Men
Research published in The Journal of Gerontology further emphasizes the role of muscle composition, this time focusing on how the density of your muscles relates to overall longevity, particularly in older men.7
This research honed in on a specific aspect of intramuscular fat measured by assessing what’s called “skeletal muscle density” and investigated its connection to mortality in a group of 1,063 older men. Muscle density is basically an indicator of how much fat is mixed in with your muscle fibers. Lower density means more fat infiltration within the muscle.
The goal was to see if having more fat within the muscle itself could predict the risk of death from any cause, as well as specifically from cardiovascular diseases. Over an average follow-up period of 7.2 years, the researchers tracked the health outcomes of these men.
They discovered that lower skeletal muscle density was significantly associated with an increased risk of both all-cause mortality — death from any cause — and cardiovascular disease mortality — death specifically from heart-related issues.
In fact, for every standard deviation decrease in skeletal muscle density, the risk of all-cause mortality increased by 24%, and the risk of cardiovascular disease mortality jumped by a significant 46%.
This study shows that as muscle density decreases — signifying more intramuscular fat — the likelihood of dying, especially from heart-related problems, rises considerably in older men. This association remained strong even after the researchers accounted for other factors that could influence mortality, such as overall body fat, fat around the trunk, lifestyle choices, existing health conditions and even frailty.
Interestingly, while intermuscular fat — the type of fat emphasized in the previous study8 — was also measured in this research, it did not show a significant independent association with mortality after these comprehensive adjustments.9
This distinction doesn’t diminish the importance of intermuscular fat, but rather adds another layer to our understanding of how different types of muscle fat impact health in distinct ways. Specifically, for older men, the density of their muscles appears to be a particularly telling sign for their long-term health and survival.10
Another study highlighted a more accessible and perhaps more directly actionable metric: body fat percentage, and how it stacks up against the commonly used BMI in predicting cardiovascular risks.11
Is Body Fat Percentage a Superior Heart Health Indicator?
Moving beyond muscle-centric measurements, a study featured in the Brazilian Journal of Medical and Biological Research provides a compelling perspective on assessing overall body composition, specifically asking whether BMI or percent body fat (PBF) is more effective at predicting cardiovascular risk.12 To explore this, researchers analyzed data from 3,859 adult Han Chinese participants who underwent routine health examinations.
The study group was divided into four categories based on whether they had normal or abnormal levels of BMI and PBF. This categorization allowed the researchers to directly compare how well each measure, BMI and PBF, correlated with various cardiovascular risk factors, such as high blood pressure, elevated blood glucose and unhealthy lipid levels.
PBF emerged as a significantly better predictor of cardiovascular risk factors compared to BMI. When researchers accounted for factors like age, gender, lifestyle and family history of obesity, they observed that PBF strongly correlated with blood glucose and lipid levels. Conversely, BMI showed a much weaker and, in some cases, non-existent correlation with these same health markers.
This is a powerful statement, suggesting that the proportion of fat in your body is more tightly linked to your cardiovascular risk than your overall weight in relation to height, which is what BMI measures.
Further, individuals with a normal BMI but an abnormal PBF — essentially those who might appear healthy weight-wise but have a high percentage of body fat — exhibited a cardiovascular risk profile similar to those with both high BMI and high PBF. This suggests that relying solely on BMI is misleading, as it underestimates the cardiovascular risks in individuals who are “normal weight obese” — having a healthy weight based on BMI but carrying too much body fat.
In essence, when it comes to predicting your risk of cardiovascular issues, your body fat percentage provides a more reliable and accurate gauge than your BMI. This is particularly important because BMI cannot differentiate between muscle mass and fat mass.13 Someone with a high BMI might be muscular and healthy, while another with a normal BMI could have excess body fat and be at higher risk.
Practical Steps to Take Charge of Your Heart Health
Now that you understand the serious implications of hidden muscle fat for your heart, the good news is that you are not powerless against this silent threat. By making informed lifestyle adjustments, you directly tackle the root causes of increased muscle fat and move toward a healthier heart. Here are four key actions to incorporate into your life, starting today.
1. Reduce your consumption of ultraprocessed foods — Ultraprocessed foods are rich in seed oils, which contain unhealthy fats like linoleic acid (LA). The primary reason why excess LA is harmful to your health is because it disrupts your cellular powerhouses — the mitochondria. Think of mitochondria as tiny energy factories in your cells that produce adenosine triphosphate (ATP), the essential fuel that keeps your cells running and repairing themselves.
Without energy, your cells can’t repair and regenerate. Further, when you consume LA, it undergoes various metabolic processes, leading to the formation of bioactive metabolites like oxidized linoleic acid metabolites (OXLAMs) and arachidonic acid (AA). These metabolites interfere with insulin signaling, a component in maintaining your blood glucose levels.
In addition, when you consume high levels of LA, your body produces more proinflammatory eicosanoids, which trigger chronic low-grade inflammation. By promoting an inflammatory environment, excessive LA consumption not only disrupts your metabolic balance but also accelerates the progression toward chronic diseases and obesity.
I recommend keeping your LA intake below 5 grams a day. To achieve this, eliminate seed oils and even fruit-based oils like olive or avocado from your diet, as these are often mixed with less expensive seed oils. Instead, use ghee, butter or beef tallow. It’s advisable to avoid dining out as well, since most restaurants use seed oils in their cooking, sauces and dressings.
Additionally, limit your consumption of chicken and pork, which are typically high in LA due to their grain-based diets.
2. Embrace strength training — If you aren’t already, make strength training a cornerstone of your exercise routine. Lifting weights or doing resistance exercises isn’t just about building bigger muscles; it’s fundamentally about improving the quality of your muscles.
Consistent strength training helps decrease fat infiltration within your muscles and increases muscle density, the very factors that studies14,15 have linked to better cardiovascular health and longevity. Aim for 30 to 60 minutes of strength training per week, targeting all major muscle groups.
3. Boost your gut health for natural weight management — Sustainable weight loss isn’t about quick fixes, it requires a holistic approach that involves gut health. A balanced gut provides a favorable environment for beneficial bacteria that assist in maintaining a healthy weight for good. For example, beneficial bacteria like Akkermansia are often lacking in those struggling with obesity.16
When Akkermansia is abundant in your gut, it acts almost like “nature’s Ozempic.” Drugs like Ozempic are synthetic versions of glucagon-like peptide-1 (GLP-1), but Akkermansia naturally boosts your body’s GLP-1. This hormone, produced by L cells in your colon, is a key player in regulating your appetite and blood sugar.
As a central coordinator, GLP-1 is intricately involved in directing your body to release insulin, delaying stomach emptying and informing your brain that you’re full. These factors naturally reduce hunger, which is why drug companies have created synthetic GLP-1 in the form of Ozempic and Wegovy.
Akkermansia is essential for a healthy microbiome, however it’s important to eliminate all seed oils from your diet for at least six months before starting an Akkermansia supplementation program.
This ensures you’re able to restore mitochondrial function and maintain a gut environment where Akkermansia can thrive. When selecting Akkermansia supplements, choose those that use advanced, timed-release capsules or microencapsulation technology.
These methods keep the bacteria dormant and protected until they reach your colon, typically within two to four hours after ingestion, ensuring that a higher number of live bacteria survive the journey through your digestive system.
4. Get an accurate measure of your body fat — Instead of relying on BMI, find out your body fat percentage. Body fat calipers and smart scales are two simple and affordable ways to track your body fat percentage. Calipers allow for a hands-on approach by measuring skinfold thickness at key areas of your body, providing a reasonably accurate estimate when used consistently.
They’re ideal for those who prefer a manual method and want to track progress over time. Smart scales, on the other hand, offer a quick and convenient alternative by using bioelectrical impedance analysis (BIA) to estimate body fat. While hydration levels affect their accuracy, they’re useful for getting a general trend of body composition. Combining both methods provides a more reliable picture of your progress.
Other more accurate measurements of obesity include waist-to-hip and waist-to-height ratios. An ideal waist-to-hip ratio is 0.7 for women and 0.8 for men. The ideal waist-to-height ratio for adults falls between 0.40 and 0.49.17
A ratio below 0.40 may suggest being underweight, while a ratio between 0.50 and 0.59 indicates excess weight and an increased risk of metabolic and cardiovascular diseases. A ratio of 0.60 or higher signals obesity and a significantly higher health risk. For children ages 6 to 18, a ratio below 0.46 is considered healthy, while anything above this threshold suggests an increased risk of obesity-related health issues.
