The BMI test has long been seen as a misleading marker of our true health status, but a new study on “Fatty Muscle Fraction” may have superseded BMI when it comes to determining the state of our bodies and our prospects for longevity.
The Body Mass Index has always been a crude calculation. It takes an individual’s height and divides the number by that person’s weight, outputting a score that makes no determination of the actual body composition of a human being. That’s why a body builder and an obese person can come out with the same negative BMI result. Another issue with the BMI test is that it doesn’t determine where fat is stored, and this is an area that scientists are becoming increasingly interested in. Apparently, those with large pockets of fat inside the muscle are at a higher risk of heart failure, but the BMI will give you no clues here.
Out With BMI, in With the Fatty Muscle Fraction
The new study, published in the European Heart Journal and led by Professor Viviany Taqueti (Director of the Cardiac Stress Laboratory at Brigham and Women’s Hospital and Faculty at Harvard Medical School, Boston, MA) sought to find a better determiner of heart health than the flawed BMI system.
“Intermuscular fat can be found in most muscles in the body, but the amount of fat can vary widely between different people,” explains Professor Taqueti. “In our research, we analyse muscle and different types of fat to understand how body composition can influence the small blood vessels or ‘microcirculation’ of the heart, as well as future risk of heart failure, heart attack and death.”
To quantify the amount of fat stored within muscles, researchers calculated the ratio of intermuscular fat to total muscle plus fat, a measurement they called the fatty muscle fraction. Patients who were being observed for the study were followed up on, for around six years, and researchers recorded whether any patients died or were hospitalised for a heart attack or heart failure.
The results showed that people who had high levels of intermuscular fat and evidence of CMD (coronary microvascular dysfunction) carried a significantly high risk of death, heart attack and heart failure. In contrast, those with larger amounts of lean muscle had a lower risk. By comparison, the fat stored under the skin (subcutaneous fat) did not increase the risk. Neither a BMI nor waist circumference test would give the same picture at the fatty muscle fraction.
“Compared to subcutaneous fat (under the skin), fat stored in muscles may be contributing to inflammation and altered glucose metabolism leading to insulin resistance and metabolic syndrome,” says Professor Taqueti. “In turn, these chronic insults can cause damage to blood vessels, including those that supply the heart, and the heart muscle itself.
“Knowing that intermuscular fat raises the risk of heart disease gives us another way to identify people who are at high risk, regardless of their body mass index. These findings could be particularly important for understanding the heart health effects of fat and muscle-modifying incretin-based therapies, including the new class of glucagon-like peptide-1 receptor agonists.
“What we don’t know yet is how we can lower the risk for people with fatty muscles. For example, we don’t know how treatments such as new weight-loss therapies affect fat in the muscles relative to fat elsewhere in the body, lean tissue, and ultimately the heart.” Professor Taqueti and her team are now assessing the impact of treatments strategies including exercise, nutrition, weight-loss drugs and surgery on body composition and metabolic heart disease.
The take home message? We already know that exercise is a great way to burn fat regardless of your BMI, but revealing your abs is just the tip of the iceberg, as your heart will thank you for being active too.
