SLIM people might still be at risk of deadly heart attacks due to hidden pockets of fat their muscles.
Researchers from Harvard Medical School compared this type of “intramuscular fat” to marbling in beef that makes it juicy and flavourful.
While flecks of fat are sought after in luxury cuts of meat like Wagyu beef, it can have serious health consequences in humans.
Harvard scientists found that women with this type of fat were at higher risk of dying from heart attack or heart failure – regardless of their body mass index (BMI).
In fact, every 1 per cent increase in the amount of fat stored in muscles increased the risk of serious heart conditions by 7 per cent.
Meanwhile, people with higher amounts of lean muscle had a lower risk.
Fat stored under the skin didn’t increase the risk of a heart attack, researchers also found.
The research looked at 669 people being evaluated at the Brigham and Women’s Hospital in Boston for chest pain and/or shortness of breath, but were found to have no evidence of obstructive coronary artery disease – a condition where the arteries that supply the heart become clogged.
The group were given scans to assess their heart function, while researchers also used CT scans to analyse body composition and measure the amounts and location of fat and muscle in sections of their torso.
Professor Viviany Taqueti, director of the cardiac stress laboratory at Brigham and Women’s Hospital, and faculty at Harvard Medical School, said: “Intermuscular fat can be found in most muscles in the body, but the amount of fat can vary widely between different people.
“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.”
Those with higher amounts of fat stored in their muscles were more likely to have coronary microvascular dysfunction (CMD), a condition that affects the small blood vessels in the heart.
[bc_video account_id=”5067014667001″ application_id=”” aspect_ratio=”16:9″ autoplay=”” caption=”I thought I just needed to crack my back but I was having a heart attack” embed=”in-page” experience_id=”” height=”100%” language_detection=”” max_height=”360px” max_width=”640px” min_width=”0px” mute=”” padding_top=”56%” picture_in_picture=”” player_id=”default” playlist_id=”” playsinline=”” sizing=”responsive” video_id=”6364747401112″ video_ids=”” width=”640px”]They were also more likely to go to hospital or die from heart disease.
According to the study, for every 1 per cent increase in fatty muscle fraction, there was a 2 per cent increased risk of CMD and a 7 per cent increase in the risk of serious heart disease in the future.
Prof Taqueti suggested that unlike subcutaneous fat – or fat stored under the skin – fat stored in the muscles may be contributing to inflammation and insulin resistance.
“In turn, these chronic insults can cause damage to blood vessels, including those that supply the heart, and the heart muscle itself,” she added.
“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.”
Prof Taqueti said it’s not yet known how to 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,” she added.
She said the findings, published in the European Heart Journal, could be “particularly important” for ongoing studies looking at the impact of weight loss drugs on heart health.
Researchers suggest it may be possible that the loss of lean muscle mass as a result of these drugs may also trigger loss fat hidden in muscles.
Prof Taqueti added: “Obesity is now one of the biggest global threats to cardiovascular health, yet body mass index – our main metric for defining obesity and thresholds for intervention – remains 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.”