When I say 'food', I don't mean a proper balanced food like you'd eat at mealtime. Drinks, whatever they are, are mostly water. But many have sugar in them. Sugar is a nutrient (carbohydrate) but too much sugar is bad: it rots your teeth and makes you fat. Drinks like cola also contain phosphoric acid which damages teeth and bones, especially in girls. Schoolgirls who drink cola are five times as likely to suffer bone fractures as girls who don't [1]. Some drinks — diet colas and so on — cut out sugar and use artificial sweeteners like aspartame and sucralose. These are not nutrients and so they don't have any calories (a measure of energy your body gets from the nutrient), unlike sugar — but they may cause other problems.

1. Active Girls Who Drink Colas Are Five Times More Likely to Fracture Bones Harvard School of Public Health, 2000.