One theory that has been embraced by Goldstein and others is that the body has not developed a system for processing sugared beverages, which are relatively new to the human diet. One study found that children who drank soft drinks consumed nearly 200 more calories per day.
The beverage industry rejects the argument that liquid calories lead to greater weight gain, pointing to a study conducted by Frank Sacks, a professor in the nutrition department at Harvard School of Public Health. The study sought to determine whether certain diets are more effective than others at achieving weight loss. Sacks concluded that diets that reduce calorie intake result in weight loss, regardless of which calories are cut.
Keane argues that the study proves his point: "a calorie is a calorie," regardless of whether it's consumed in solid or liquid form.
But Sacks disagrees. "I don't know how they possibly could come up with that kind of interpretation," Sacks said. "There was no testing of sugar-containing beverages, and in fact the participants were taught to avoid them."