We talk a lot about ''watching what we eat,'' but if you never gave a thought to what you ate and instead watched only what you drank, you could probably cut 450 calories a day out of your life. (Yes, nearly a pound of fat loss a week!) That's what a study from the University of North Carolina found. Americans today drink about 192 gallons of liquid a year—or about 2 liters a day. To put it into perspective, this is nearly twice as many calories as we did 30 years ago.
When confronted with the growing tide of calories from sweetened beverages, the first response is, “Why not just drink diet soda?” Well, for a few reasons:
Just because diet soda is low in calories doesn't mean it can't lead to weight gain.
http://health.yahoo.com/experts/eatthis/22630/the-truth-about-diet-soda/