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1 in obesity fight Pushing her meal cart into the hospital room, a research assistant hands out tall glasses of reddishpink liquid, along with a gentle warning: "Remember, you guys have to finish all your KoolAid."

One by one, young volunteers chug down their drinks, each carefully calibrated to contain a mix of water, flavoring and a precisely calibrated solution of high fructose corn syrup: 55% fructose, 45% glucose.

The participants are part of an ongoing study run by Kimber Stanhope, a nutritional biologist at the University of California, Davis. Volunteers agree to spend several weeks as lab rats: their food carefully measured, their bodies subjected to a steady dose of scans and blood tests. At first, each volunteer receives meals with no added sugars. But then, the sweetened drinks start showing up.

For the final two weeks of the study, volunteers drank three of the sweet concoctions daily about 500 calories of added sugar, or 25% of all calories for the adult women in the study. Within just two weeks, their blood chemistry was out of whack. In one striking change, the volunteers had elevated levels of LDL cholesterol, a risk factor for heart disease.

While forcefeeding junk food may sound extreme, this controlled diet is not so far from the real world. Department of Agriculture (USDA). That single drink is more than 10% of the total calories an adult woman needs to maintain a healthy weight, according to USDA diet guidelines. Meanwhile, about 1 in 4 Americans gets at least 200 calories a day from sugary drinks. These numbers, along with work like Stanhope's, gives ammunition to doctors and public health officials who say soda should be treated as public health enemy No. 1.

"Soft drinks and sugarcontaining beverages are the low hanging fruit in public health today," says Dr. David Ludwig, director of the New Balance Foundation Obesity Prevention Center, at Children's Hospital in Boston. "Many children are consuming 300 calories per day or more, just in sugarcontaining beverages. Compare the challenge of giving up three glasses of sugary beverages, versus getting them to do two hours of moderate physical activity."

"If you switch from Coke to water, that's easy," says Elizabeth MayerDavis, a professor at the University of North Carolina and a recent president of the American Diabetes Association. "You don't have to make big complicated changes in how you cook, and shop, and all that. And the number of calories you can save, can be substantial."

Some in the soft drink business say their product has been unfairly singled out. "Consumption of added sugars is going down," says Karen Hanretty, VicePresident of Public Affairs for the American Beverage Association. "Soda consumption has declined, even as obesity has increased. To say that sugar is solely responsible for obesity, doesn't make sense."

CocaCola has adapted to meet consumer demand, says Rhona Applebaum, the company's Vice President and Chief Scientific Regulatory Officer. More than ever, she says, those consumers choose lowsugar products. Today, Diet Coke and Coke Zero make up 41% of Coke's North American soda sales, up from 32% a decade ago. "Our products are part of a balanced, sensible diet, and they can be enjoyed as a valuable part of any meal, including snacks," says Applebaum.