Hidden fat around your waist ‘increases the risk of early death from heart attack and cancer’
How much fat you have around the middle and its density was more important than BMI and waist circumference, in judging health
Having a spare tyre is more dangerous for the heart than previously thought.
Having "love handles" or the visible flab of fat just under the skin may be protective.
But how much "hidden" fat you have around the belly and how dense it is is just as important as how fat you are elsewhere.
A new study found increased belly fat and its density was more important than body mass index (BMI) and waist circumference, two commonly used methods to estimate whether someone is a healthy weight or not.
It adds to previous findings that showed those that carry excess abdominal fat tend to face higher risks of heart disease compared to people who have fat elsewhere.
Abdomen fat was also linked to higher risks of cancer, cardiovascular events and death.
Assistant clinical professor of medicine, Dr Caroline Fox said: "What's really interesting is that we show that an increase in the amount of stomach fat and a lower density fat is associated with worse heart disease risk factors - even after accounting for how much weight was gained.
"This hasn't been shown before."
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The former senior investigator for the National Heart Lung and Blood Institute added: "Measuring fat density is a new measure that we are still working to understand and warrants further investigation.
"We used it as an indirect measure of fat quality and found that lower numbers were linked to greater heart disease risk."
The study explored whether there was a link between anatomical changes in belly fat - both its volume and density - and changes in a broad array of cardiovascular disease risk factors during the average six-year study period.
It looked at subcutaneous adipose fat, the fat just under the skin and visceral adipose fat, the fat inside the abdominal cavity,
CT scans were done on 1,106 middle aged participants from the Framingham Heart Study.
We show that an increase in the amount of stomach fat and a lower density fat is associated with worse heart disease risk factor... this hasn't been shown before
Dr Caroline Fox
Over the six-year follow-up period, participants had a 22 per cent increase in fat just under the skin and a 45 per cent increase in fat inside the abdominal cavity on average.
In general, increases in the amount of fat and decreases in fat density were correlated with adverse changes in heart disease risk.
Each additional pound of fat from baseline to follow up was associated with new onset high blood pressure, high triglycerides and metabolic syndrome.
Even though increases in both types of fat were linked to new and worsening cardiovascular disease risk factors, the relationship was even more pronounced for fat inside the abdominal cavity compared to fat just under the skin.
In particular, individuals with greater increases in fat inside the abdominal cavity showed substantial increases in metabolic risk factors including high blood sugar, high triglycerides and low HDL, or good cholesterol.
Dr Fox said that higher levels of fat just under the skin may actually be protective because it serves as a "metabolic sink for storing excess fat particles."
Abdominal cavity fat, on the other hand, is thought to be more dangerous.
Overall, associations remained significant even after adjusting for changes in BMI or waist circumference.
Those with greater increases in fat volume and more decreases in fat density had
relatively higher incidence of heart disease risk factors.
Commenting on the findings Dr James A de Lemos said the findings support a growing body of literature that suggests identifying the location and type of fat deposits can provide important information about the risk of heart disease not found in the simple BMI measurement.
Dr Fox said future research to understand fat density, and why and how it is associated with metabolic consequences of obesity was needed.
The study was published in the Journal of the American College of Cardiology.