Some people therefore have pockets of fat hidden in their muscles and these same people are at higher risk of hospitalization and death from cardiovascular causes. This is true regardless of their body mass index (BMI). Lead author Dr. Viviany Taqueti, a professor at Harvard Medical School, adds: “Obesity is one of the greatest global threats to cardiovascular health today, but body mass index – our main indicator to define obesity and intervention thresholds – remains a controversial and erroneous marker of cardiovascular prognosis. This is particularly true in women, in whom a high BMI may reflect more ‘benign’ types of fat.
This “intermuscular” fat has until now been little studied,
even if in humans, it is indeed the equivalent of animal fat (saturated fatty acids) popular in entrecôtes, but not recommended for health, emphasize the authors. However, in humans, little is known about its impact on health. Intermuscular fat can be found in most muscles in the body, but the amount of fat can vary greatly from person to person.
This is indeed the first research to examine the effects of different fatty muscles and different types of fat in terms of heart risk, 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.
The study followed for 6 years 669 patients, aged on average 63 years, 70% women, followed at the BWH for chest pain and/or shortness of breath, presenting a priori no sign of obstructive coronary artery disease (when the arteries which supply the heart are obstructed). The participants all had a cardiac PET scan to assess the functioning of the heart and tscans to assess body composition, amounts and location of fat and muscle in a part of the torso. The researchers finally calculated the ratio between intermuscular fat and total muscle plus fat: this measurement was called
“the fatty muscle fraction”.
Data analysis during monitoring reveals that:
-- participants with higher amounts of fat stored in their muscles have an increased risk of damage to the micro blood vessels that serve the heart (coronary microvascular dysfunction);
- are at increased risk of hospitalization and death from cardiac causes;
- for every 1% increase in muscle fat fraction, the risk of coronary microvascular dysfunction increases by 2% and the risk of future serious heart disease by 7%;
- these associations still hold after taking into account possible confounding factors and BMI;
- high levels of intermuscular fat and signs of coronary microvascular dysfunction are associated with a particularly high risk of death, heart attack and heart failure;
- in contrast, higher amounts of lean muscle are associated with lower risk;
- the analysis also confirms that fat stored under the skin (subcutaneous fat) does not increase these risks.
“Compared to subcutaneous fat, intramuscular fat can contribute to inflammation and impaired glucose metabolism, lead to insulin resistance and metabolic syndrome. These chronic conditions damage blood vessels, including those that supply the heart, and the heart muscle itself.explain the authors.
It is now a matter of studying, with this new perspective, the effects on intramuscular fat of therapies based on incretins – which modify fat and muscles – and of the new class ofGLP-1 agonists.
“What we don’t know yet is how we can reduce the risk for people with fatty muscles,” but this new finding proves, in any case, that existing measures, such as those targeting the index body mass or waist circumference, are not sufficient to accurately control the risk of heart disease.
Health
