Bit of a tangent, but can you elaborate on that aspartame comment? I've found it difficult to research aspartame risks online, since the vast majority of what comes up appears to be unsubstantiated FUD, and the official sources (FDA etc.) don't appear to recognize any risk whatsoever. There does seem to be a general public perception that aspartame is "bad for you" in some way though.
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.
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.
