By lowering appetite suppressant chemicals and encouraging sugar cravings, artificial sweeteners raise your odds of weight gain. They also promote insulin resistance and related health problems, just like sugar. Below are two videos describing some of the down-sides of consuming any sweetened or artificially sweetened beverage.
Personally, nearly six years ago I was diagnosed with MS. During my bodybuilding career I did consume a decent amount of diet soda during my pre-competition and competition season. Here is a video that gets into some of the diseases that may be linked to all artificial sweeteners.
I strongly recommend avoiding all artificial sweeteners, not just aspartame, and to read food labels to make sure you’re not inadvertently consuming them. They’re added to some 6,000 different beverages, snacks and food products, so there’s no telling where they might be hiding. For safer sweetener options, you could use stevia or Lo Han, both of which are natural sweeteners.