The percentage of calories Americans consume from restaurant fast food such as hamburgers and pizza declined slightly in a new government report, but officials say its too early to declare this a trend. In the latest survey from the US Centers for Disease Control and Prevention, covering 2007 to 2010, Americans adults said they got more than 11% of their calories from fast-food eateries. That was down from almost 13% in the previous survey, which spanned 2003 to 2006. One factor may simply be the aging of the US population: While those ages 20 to 39 reported eating more than 15% of daily calories from fast-food sources, that fell to just 6% for people over 60. The more people weighed, the greater the percentage of calories consumed came from fast food, and those eating the most fast food-18% of calories-were obese young adults.