I think there answer (like a lot of stuff ) lies somewhere in the middle. If you are big on "diet" products then your aspartame use will be a lot higher than someone who uses in moderation. High dose over prolonged periods "could" overwhelm your liver.
I think there are some people who don't metabolize it well and this chemical causes them grief. Then there are others who can shovel boat loads of the stuff down the pipe and never experience anything detrimental.
Sweetener headaches are a very common complaint amongst users.
If it is a concern, your bigger goal is squashing the sweet tooth.
Splenda or stevia "may" be safer alternatives. There's many protein powders that incorporate those alternatives.
BTW, what's gaake sugar? Or did you mean fake sugar?