Calories in versus calories out.
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Dr. George Bray
Chief of clinical obesity and metabolism at Pennington Biomedical Research Center

Dr. George Bray graduated from Harvard Medical School in 1957 and has since spent nearly all his time studying obesity. Now, at 81, Bray is arguably the most influential, oft-published figure in the research world of obesity. Chief of obesity and metabolism at Louisiana's Pennington Biomedical Research Center, Bray is most noted for developing the "calories in-calories out" theory – that people gain weight when they eat more calories than they burn.

Bray believes there's no insidious reason behind the rise in obesity. Some people have control around food while others eat more than they should "because it tastes good," he says. Bray admits recent research has added nuance to his calories in-calories out theory: Calories in beverages like soft drinks and fruit juices pack a worse punch because they contain fructose, or fruit sugar, which the body converts more readily into fat than other sugars. Liquid calories also do more damage than solid food, because they pass through the stomach more quickly. Aside from these exceptions, "cumulative calories are unequivocally the thing that is causing obesity," he says. Which means you'd gain weight as easily eating too much pasta as you would eating steak.

Bray believes government corn and sugar subsidies have driven up the availability of cheap, nutritionally void, high-caloric food and candy: "The government caused the problem. Don't they have to do something about it?" Bray says subsidies should be removed and food advertising aimed at kids limited.