http://en.wikipedia.org/wiki/Phenylketonuria http://en.wikipedia.org/wiki/Phenylketonuria is a real and serious genetic condition. It's why diets sodas have a

http://en.wikipedia.org/wiki/Phenylketonuria http://en.wikipedia.org/wiki/Phenylketonuria is a real and serious genetic condition. It's why diets sodas have a mandatory "Phenylketonurics: Contains phenylalanine." label. As to the other "generally bad for you" ideas, they're not solidly substantiated. The idea that artificial sweeteners somehow lead you to eat more by messing up feedback regulation is actively studied, but I wouldn't say established. However: http://www.mayoclinic.org/healthy-living/nutrition-and-healthy-eating/expert-answers/phenylalanine/faq-20058361 http://www.mayoclinic.org/healthy-living/nutrition-and-healt... Phenylalanine is one of the amino acids that you always need and have around in some quantities. But if you get too high a concentration in the brain, it becomes too easy to make the neurotransmitter Phenethylamine. That's got a list of possible effects for different people - could be a stimulant, could be a migraine trigger - but, especially since it doesn't do the same thing for everybody, there is no consensus for what it does. Nor have I seen good numbers on how much is too much.