Studies suggest that where people tend to store their extra calories as fat may be at least as big a threat to health as how much total fat they have.
There's mounting evidence that people who are genetically programmed to store fat in the area around the heart and under the breastbone in the chest, where it sits in close proximity to the heart, may face a higher risk of heart disease compared to people who store fat in other areas.
The new study, which is published in the journal Radiology, used specialized imaging techniques to measure fat that surrounds the heart in 183 men and women.
The scans were also able to see the beginnings of plaques, or blockages, in the coronary arteries, the vessels that carry blood to the heart muscle.
Researchers found that the amount of fat stored around the heart and in the chest was a stronger predictor of the heart's health than overall size or the amount of belly fat a person had.
"If you look at the fat around their hearts, it is better at predicting the disease than the fat in the stomach or other areas that we traditionally look at," says study researcher David A. Bluemke, MD, PhD, director of radiology at the National Institutes of Health Clinical Center in Bethesda, Md.
Fatty tissue releases inflammatory chemicals that may speed the development of atherosclerosis, says study researcher Jingzhong Ding, PhD, an associate professor of internal medicine and geriatrics at the Wake Forest University School of Medicine, in Winston-Salem, N.C.
"We think that the fat, because it releases lots of these different kinds of chemicals, has a detrimental effect on surrounding organs and tissues," Ding tells WebMD.
Chest Fat and Heart Health
For the study, which was funded by the National Heart Lung and Blood Institute, researchers recruited middle-aged adults who had never been diagnosed with heart disease.
Using cardiac magnetic resonance imaging scans (cardiac MRI) and computed tomography (CT) scans, researchers found that the more fat a person had in their chest, the more abnormal their arteries looked.
That relationship persisted, even when researchers subtracted the influence of other factors, like BMI, waist size, and coronary artery calcium scores.
But the link between chest fat and heart disease was stronger for men than for women.
Researchers say that may be because estrogen protects most women from developing heart disease until after menopause.
"The development of coronary artery disease in women usually takes about 10 years longer," Bluemke says. "At a particular age range, men will be more advanced."
He says further research, with more refined imaging techniques, will be needed to demonstrate the same relationship in women.
Until researchers know more, people who are worried about their risk of heart disease may take comfort in the results of another small study, which found that overall weight loss may help reduce chest fat, too.
The study, published in May in Medicine & Science in Sports & Exercise, found that 32 women who lost weight over five months lost about 17% of the fat around their hearts, whether they did it with diet alone or diet and exercise.