Caffeine however does not slow down weight loss as stated in a post. Caffeine is a stimulant hence it actually enhances one's weight loss due to it's effect on our body due to more energy to do things hence enhancing weight loss more. Caffeine is actually an added ingredient to most diet pills due to this feature. The soda's effect on one's weight loss doesn't have anything to do with the caffeine as explained above. It's due to the sugar content and calories hence one's weight gain.