@Glomoro That is more commonly about examining metabolism (commonly liver function), rather than some measure of purity. A healthy person always has a measure of blood sugar etc., regardless whether you eat or not. In the first place, "purity" is an incredibly ill-defined word in this matter to be even easily considered (how tf you even define it?).
@Mna 'Tis true. Which is why I only discussed the realistic approach to it in here, not the fantastical element. Not to fault Glomoro, either, as a bit of theorycrafting for fun is pretty much what comments are there for (at least for me, lol).