It’s possible that some drinks actually have no calories, but this is unlikely. The FDA Food Labeling Guide for the food industry allows manufacturers to list a food as no or zero calorie as long as the food has no dietary significance. This simply means that any drink with a calorie value less than 5 can be labeled as zero-calorie or no-calorie. One such example is Coke Zero. I honestly have no idea how many calories are really in Coke Zero. Maybe there are really no calories! But the point is that they can call it that, and claim no calories as long as there are less than 5 calories per serving.
If you would like to learn more about the FDA Food Labeling guide, you can read the latest release at:
http://www.cfsan.fda.gov/~dms/2lg-toc.html
So how many calories in a zero calorie drink? Your guess is as good as mine, but at least we know its less than 5 calories per drink! If you keep track of your calories, just log it as 5 calories to be sure. The good news is that you can essentially have a serving and not worry to much about your body storing excess calories as fat as there are no significant calories to worry about. However, you should note that this is not a free pass to drink as many diet drinks, as you want to. Many if not most of these drinks are sweetened with aspartame, which is believed to cause long-term health problems. If you are drinking soda, most of them have caffeine, which can also cause problems if consumed in excess.
The bottom line is that many if not all zero calorie drinks have some calorie content, just not significant enough to worry about for only 1 serving. If you drink diet drinks, especially soda, make sure you consume them at a moderate frequency or lower. The majority of your liquid intake needs to be from drinking water. So drink lots of water every day, and consume sweet diet drinks as sparingly as possible.
