Not so. While the wife shops at Costco I normally set in the snack bar having a goodie. While there I watch to see what drinks skinny people select at the self serve drink station and what overweigt people select. I almost never see an overweight individual select a diet drink. Skinny and normal weight people select diet drinks about 60% of the time.
I cannot stand the taste of diet sodas, definitely has to be an acquired tolerance. So, you would see me picking regular soda. But, I rarely drink a full regular soda. Takes me about a week to 10 days to drink a soda.
Drink about a gallon of water a day, though.