People who are slim but have hidden pockets of fat within their muscles are at increased risk of deadly heart conditions, new research shows.
Researchers from Harvard Medical School studied “intramuscular fat”, similar to the fat found in prized Wagyu beef, and found that women with this type of fat had a higher risk of dying or being hospitalised from heart attack or heart failure - regardless of their body mass index.
Researchers looked at 669 women who were being monitored at the Brigham and Women’s Hospital for chest pain or shortness of breath, but who did not have any existing evidence for coronary artery disease.
The research, published in the European Heart Journal on Monday, found that women with high levels of intermuscular fat had an “especially high risk” of heart attack or failure, with every 1 per cent increase in the proportion of fat stored in muscles increasing the risk of future serious cardiac events by 7 per cent.
The research also found that people with higher amounts of lean muscle had a lower risk, and concluded that fat stored under the skin did not increase the risk of a heart attack.
Professor Viviany Taqueti, director of the cardiac stress laboratory at Brigham and Women’s Hospital and faculty at Harvard Medical School, said that compared to fat under the skin, fat stored in muscles might be contributing to inflammation and changed glucose metabolism, which can lead to conditions that can damage blood vessels.
“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,” she said.
“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.”
Prof Taqueti, who led the study, said while obesity was “one of the biggest global threats to cardiovascular health” the body mass index remained a “controversial and flawed marker of cardiovascular prognosis”.
“This is especially true in women, where high body mass index may reflect more ‘benign’ types of fat,” she said.
All the patients had their heart function assessed and the researchers used CT scans to analyse each patient’s body composition, including the amount of fat and muscle. The patients, who had an average age of 63, were then followed up after six weeks, and researchers recorded whether any had died or been hospitalised for a heart attack or heart failure.
In an editorial for the journal, Dr Ranil de Silva from Imperial College London and colleagues noted there were limitations to the research, including the fact it was an observational study done retrospectively, and details including insulin resistance, diet or exercise performance were not included.
Dr de Silva said the research was intriguing and highlighted a group of patients at increased risk, and hoped the work prompted further study.
