"According to research, aspartame actually contributes to weight gain as opposed to weight loss. The assumption is that because aspartame doesn’t contain the calories sugar does, you lose weight, but the exact opposite appears to be true in the case of aspartame. Studies have found people actually gain more weight consuming aspartame than people consuming regular sugar! Most likely, this is because weight is regulated by insulin and leptin, and aspartame negatively affects both of these hormones."
It can be found here.
Throw out your diet soda. If you are going to drink soda, you should not cut any corners on your health. Face the sugar head on!