Drinking sugar-sweetened beverages like soda daily may lead to more abdominal fat gain over time, according to a new study.

So-called visceral fat in the midsection wraps around internal organs like the liver and pancreas and affects the function of hormones like insulin. Insulin dysfunction, and becoming resistant to insulin, is closely tied to type 2 diabetes and heart disease risk.

"A lot of prior studies have looked at sugar-sweetened beverages and obesity," said lead author Dr. Caroline S. Fox. "We looked at body fat distribution, in particular change over time."

Fox, a former investigator with the Framingham Heart Study of the National Heart, Lung, and Blood Institute, is currently a special volunteer with the National Institutes of Health.

She and her colleagues found that all participants tended to gain visceral fat over time, but those who drank sugary beverages daily gained more.

The researchers used data from about 1,000 adult participants in the Framingham Heart Study in Framingham, Massachusetts, who answered food frequency questions about sugar-sweetened beverages and diet soda.

Sugar-sweetened beverages like regular soda and fruit punch have added sucrose or high fructose corn syrup. Most participants said they drank a mixture of sugary beverages and diet soda.

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About a third said they never consumed sugar-sweetened beverages, 20 percent did so occasionally, 35 percent drank them frequently and 13 percent drank them daily.

At the study start, they underwent a computed tomography scan to measure quantity and volume of abdominal fat tissue. Six years later, they underwent another scan.

Over that period, visceral fat volume increased by 658 cubic centimeters for non-drinkers, slightly more for occasional and frequent drinkers, and by 852 cubic centimeters for daily drinkers of sugary beverages, as reported in the journal Circulation.

For daily drinkers, that's in increase of about 0.8 kilograms, or 1.8 pounds, of abdominal fat, Fox told Reuters Health by phone.

"That's probably a very small difference of actual visceral fat," but it's enough to make a difference for metabolic risk, according to other studies, she said.

Diet soda wasn't linked to an increase in visceral fat.

It's not clear from this study whether decreasing sugary beverage intake would decrease the gain in visceral fat over time, Fox said.

The American Heart Association recommends a limit of 100 calories per day of added sugars, such as those found in sweetened beverages, for most women, and 150 calories per day for most men.

"Drinking one 12-ounce soft drink a day would exceed that amount - and while they are a major source, sugar-sweetened beverages contribute only about half of the added sugar consumed by Americans," said Jean Welsh of Emory University in Atlanta, who was not part of the new study.

"Water and milk are the healthiest beverage choices," Welsh told Reuters Health by email. "Sugary beverage consumers who are looking to reduce their sugar and calorie consumption may find that diet soda consumption helps - but only as long as they are careful to not eat more of something else."