When I was a teen, I had some problems with compulsive overeating. When I would binge, I'd start to feel full, and then I'd get a diet coke. It allowed me to finish the bag of potato chips, eat another frozen pizza, etc. I do not doubt that it can increase appetite.

It's been a long time since I did that, and a long time since I drank diet coke regularly. If I try it now, my body freaks out-- headache, diarrhea, etc. I avoid aspartame like the plague.