Full disclosure I'm going completely tangential for this one.
I find it believable at best that aspartame can cause cancer, but causing weight gain just makes no sense to me.
I used to be FAT. 250 lbs. I didn't really make that many changes to my diet, except for cutting refined sugars way back.
I switched to Diet Coke, got off the little debbies, and I slimmed right down and now I'm hovering around 135.
It would make sense to say that I would maintain that weight or maybe gained more if aspartame was as harmful as this article says, but I'm not seeing it.