Wow... lot's of good responses here and lot's of vitriol!!!! The harshest of these comments seem to be steeped in falacy that 'calories' make you gain fat. If I add 200 calories of fat or 200 calories of starch to my meal, which meal causes me to gain more 'fat' or 'weight'? According to all of you that assume Diet Coke cannot possibly make you gain weight because it has no calories, both of my meal choices should end with the same net result, right? Wrong. Weight gain and adiposity are dependent upon INSULIN, not calorie balance. Back to diet coke: when the body 'tastes' something sweet, regardless of whether or not it has sugars or any caloric density whatsoever, there is a cephalic phase insulin response and insulin is secreted, causing the food you are eating to be stored as fat or if you are drinking the soda alone, for much of your blood glucose to be scavenged and stored as fat. With that drop in BG, you get HUNGRY fast and your body is screaming for carbs.

Diet coke most certainly makes you fat. As does Stevia, as does Blue Agave Nectar, as does ANYTHING that adds an overtly sweet tasted to what you eat. You want sweet? eat an apple and some almonds. Slow gastric emptying from the almonds fat, nice fiber to slow down the process as well, and just what nature intended for you to eat. Or you could just eat that near formaldehyde crap in diet coke and stay fat. You make the call.