How wrong can you diet that is calorie-free Coke be for your belly? Belt-bustingly bad, researchers say. A study within the journal Diabetes pro found that individuals who drank two or more diet sodas a had waist-size increases that have been six times greater than non-drinkers day. Diet products are loaded with deceptively sweet artificial sweeteners, which, researchers say, trick the metabolism into thinking sugar is well under way, spike insulin levels, and shift the body from a fat-burning to a state that is fat-storing.