regular soda. But they've done studies that show that people who drink diet soda consume 200 more calories on average during the day than people who don't and this is likely due to the fact that when you consume artificial sweeteners, your body is less likely to suppress ghrelin, the hormone that makes you hungry. So diet soda essentially makes you feel hungrier throughout the day, which makes staying on a diet more difficult. If people are craving soda, we typically recommend they make fruit water. i.e. stick some lemon, orange, kiwi slices etc... in a pitcher of water and drink the flavored water. You can also buy fruit water premade at a lot of the soda shops like Sodalicious, Swig, etc... and it's pretty cheap.