Carrying too much fat around the abdomen puts people at greater risk for heart disease and cancer compared with people who have a similar body mass index (BMI) but who carry their fat in other parts of the body.
So says a US study published online in the July issue of the Journal of the American College of Cardiology.
Previous studies have shown that the risk of disease and death linked to obesity or being overweight varies among individuals with the same BMI (body mass index - the ratio of their weight in kilos to their height in metres squared).
Now a new study suggests ectopic fat - that is, fat present where it shouldn't be, in this case the highly visible spare tyre(s) around the middle - might explain this variation.
We already know that carrying excess fat around the waist can be more dangerous than carrying it elsewhere, such as the hips or the thighs (apple-shaped as opposed to pear-shaped).
But this latest study, from lead author Kathryn A. Britton, instructor of medicine at Brigham and Women's Hospital in Boston, and colleagues, is the first to use CT scans to see which specific deposits of excess fat are linked to disease risk.
Data from important big study
The study uses data collected in the Framingham Heart Study from 3,086 participants who were followed for up to seven years. Their average age was 50, and around half were women.
The physical exams the participants underwent at the start of the Framingham study period included CT scans, which allowed the researchers on this study to assess ectopic fat deposits in the abdomen, around the heart and around the aorta, the largest artery in the human body.
Over the follow-up, there were 90 heart-related events, 141 cases of cancer, and 71 deaths (from all causes) among the participants.
When Britton and colleagues analyzed these in relation to the fat deposits, and took out the effect of clinical risk factors and BMI, they found abdominal fat was linked to heart disease and cancer.
First study to factor in belly fat for cardiovascular risk
This study is the first to show that when you add presence of belly fat to measures that compare BMI to waist size, the ability to predict cardiovascular risk improves.
Although the researchers didn't investigate why fat in the abdomen is tied to higher risk for heart disease and cancer, they conclude their findings support the growing idea that ectopic fat has "a pathogenic role".
One possible explanation could be to do with the fact belly fat often indicates there is too much fat around internal organs.
Britton says findings like these are valuable because, given the worldwide obesity crisis, it is important to identify individuals at high risk so that prevention and therapy can be tailored specifically for them.
Britton's study comes after one published in 2012 in which researchers at the Mayo Clinic found belly fat increases the risk of death even in people of normal weight.Written by Catharine Paddock PhD