Belly fat – especially hidden fat deep in the gut – may indicate increased risk for heart disease, a new study suggests.
The six-year study of more than 1,000 adults found people with a "spare tyre" in their midsection had a greater risk for heart disease compared to those with visible flab elsewhere under the skin – or "love handles."
"Adipose tissue (fat in the stomach) along with fat below the skin has been associated with abnormalities, including high triglyceride levels, low HDL levels (good cholesterol), high blood pressure and greater risk of diabetes," said Dr Gregg Fonarow. He is a professor of cardiology at the University of California, Los Angeles, and had no part in the new study but is familiar with the findings.
The study looked at abdominal fat quantity and quality.
The researchers cautioned, however, that the study only showed an association between belly fat and potential heart disease, not that belly fat causes heart disease.
Read: The type of belly fat that matters
Fonarow said perhaps deep abdominal fat is unhealthier because it might increase insulin resistance, which can lead to high blood sugar and type 2 diabetes.
"This study suggests individuals even with a body mass index in the normal or overweight category but who have increased abdominal mass – a pot belly – may be at increased cardiovascular risk," Fonarow said.
The study was led by Dr Caroline Fox, a former senior investigator for the US National Heart, Lung, and Blood Institute. She and her team collected data on 1,106 men and women, average age 45, who took part in the long-running Framingham Heart Study. All agreed to have their stomachs scanned to determine the amount of their belly fat.
Read: Extra weight does increase heart disease risk
Over six years, the researchers found that increases in the amount of fat and decreases in fat density were linked with changes in the risk for heart disease. Each additional pound of fat was associated with newly developed high blood pressure, high triglycerides and metabolic syndrome, which includes high cholesterol and increased odds of type 2 diabetes, the researchers said.
Although increased fat was linked to new and worsening heart disease risk factors overall, the risk was greater for fat inside the abdomen, compared with fat just under the skin, the researchers said.
Limitations of BMI
People whose deep stomach fat increased had significant rises in high blood sugar, high triglycerides and low levels of HDL cholesterol, Fox's team said. These associations remained significant even after the researchers accounted for changes in weight and waist size.
The report was published in the Journal of the American College of Cardiology.
Read: Body fat tied to heart risks in normal-weight adults
Some experts say identifying the location and type of body fat provides valuable information – perhaps better than that from body mass index (BMI), a current tool that calculates body fat based on weight and height.
"This study supports a growing body of literature demonstrating that adipose tissue imaging provides important information about cardiovascular risk not contained in the measurement of BMI alone," said Dr Ian Neeland. He is an assistant professor of cardiology at the University of Texas Southwestern Medical Centre at Dallas and co-author of an accompanying journal editorial.
Abdominal tissue scanning is emerging as a new way to assess heart disease risk and address many of the limitations of the simple BMI measurement, Neeland said. "It may be time to retire the BMI in favour of these novel adipose tissue deposits in clinical and research practice," he added.
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