Fat muscle increases risk of serious heart disease, regardless of overall body weight, study finds

People with hidden pockets of fat in their muscles are at higher risk of dying or being hospitalized from a heart attack or heart failure, regardless of their body mass index, study finds published in the European Journal of the Heart.

This “intermuscular” fat is very popular in beef steaks intended for cooking. However, little is known about this type of body fat in humans and its impact on health. This is the first study to comprehensively investigate the effects of fatty muscle on heart disease.

This new finding adds evidence that existing measures, such as body mass index or waist circumference, are not adequate to accurately assess heart disease risk for everyone.

The study was led by Professor Viviany Taqueti, Director of the Cardiac Stress Laboratory at Brigham and Women’s Hospital and faculty at Harvard Medical School, Boston, USA.

She said: “Obesity is now one of the biggest global threats to cardiovascular health, but body mass index – our main indicator for defining obesity and thresholds for intervention – remains a controversial marker and imperfect cardiovascular prognosis. This is especially true in women, where a high body mass index may reflect more “benign” types of fat.

“Intermuscular fat can be found in most muscles in the body, but the amount of fat can vary greatly from person to person. In our research, we analyze muscles and different types of fat to understand how the composition Physical activity can influence the small blood vessels or ‘microcirculation’ of the heart, as well as the future risk of heart failure, heart attack and death. “

The new research looked at 669 people who were being evaluated at Brigham and Women’s Hospital for chest pain and/or shortness of breath and who had no signs of obstructive coronary artery disease (where the arteries that supply blood to the heart become dangerously blocked). These patients had a mean age of 63 years. The majority (70%) were women and almost half (46%) were non-white.

All patients were tested with cardiac positron emission tomography/computed tomography (PET/CT) to assess how their hearts were functioning. The researchers also used CT scans to analyze each patient’s body composition, measuring the amount and location of fat and muscle in a section of their torso.

To quantify the amount of fat stored in muscles, the researchers calculated the ratio of intermuscular fat to total muscle plus fat, a measure they called muscle fat fraction.

The patients were followed for about six years, and researchers recorded whether any patients died or were hospitalized for a heart attack or heart failure.

Researchers found that people with higher amounts of fat stored in their muscles were more likely to experience damage to the tiny blood vessels that serve the heart (coronary microvascular dysfunction, or CMD), and they were more likely to die. or being hospitalized for heart disease.

For every 1% increase in fat muscle fraction, there was a 2% increase in the risk of CMD and a 7% increase in the risk of future serious heart disease, regardless of other known risk factors and the body mass index.

People with high levels of intermuscular fat and signs of CMD were at particularly high risk of death, heart attack and heart failure. In contrast, people with a greater amount of lean muscle mass had a lower risk. Fat stored under the skin (subcutaneous fat) does not increase the risk.

Professor Taqueti said: “Compared to subcutaneous fat, fat stored in muscle can contribute to inflammation and impaired glucose metabolism, leading to insulin resistance and metabolic syndrome. . In turn, these chronic insults can damage blood vessels, including those that feed blood vessels. heart and the heart muscle itself.

“Knowing that intermuscular fat increases the risk of heart disease gives us another way to identify people 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 newer class of glucagon-like peptide-1 receptor agonists.

“What we don’t know yet is how we can reduce the risk for people with fatty muscle. For example, we don’t know how treatments such as new weight loss therapies affect fat in the muscles versus fat elsewhere in the body, lean tissue and ultimately the heart.

Professor Taqueti and his team are evaluating the impact of treatment strategies including exercise, nutrition, weight loss drugs or surgery, on body composition and metabolic heart disease.

In an accompanying editorial, Dr Ranil de Silva of Imperial College London and colleagues said: “Obesity is a public health priority. Epidemiological studies clearly show that obesity is associated with increased cardiovascular risk, although this relationship is complex.

“In this issue of the journal, Souza and colleagues hypothesize that skeletal muscle quantity and quality associate with CMD and modify its effect on the development of future adverse cardiovascular events, independent of mass index. body (BMI).

“In this patient population who were predominantly female and had a high rate of obesity, the main findings were that increasing levels of intermuscular adipose tissue (IMAT) were associated with greater occurrence of CMD, and that the presence of Both high IMAT and CMD were associated with the highest rate of future adverse cardiovascular events, with this effect independent of BMI.

“The interesting results provided by Souza et al are hypothesis generating and should be interpreted in the context of several limitations. This is a retrospective observational study. While a number of potential mechanisms are suggested to explain the relationship between elevated IMAT and impaired coronary flow reserve, these were not directly assessed.

“In particular, no details on circulating inflammatory biomarkers, insulin resistance, endothelial function, diet, skeletal muscle physiology or exercise performance were given.

“The data presented by Souza et al are intriguing and further highlight CMD patients as a patient population at increased clinical risk. Their work should stimulate further research into establishing the added value of markers of adiposity compared to conventional and emerging cardiac risk stratification in order to identify patients who may benefit prognostically from targeted cardiometabolic interventions.