Gut neurons (neuropod cells) can distinguish between real sugars and artificial sweeteners and signal this difference to the brain.

“What they showed was there's a category of neuropod cells that recognize sugar in the gut and signal that information about the presence of sugar in the gut to the brain via the pathways we talked about before, the nodose ganglia, the vagus, dopamine, et cetera, et cetera. Interestingly, the very same category of neurons can respond to artificial sweeteners and signal that information to the brain, but the pattern of signaling and indeed the signature pattern that is conveyed to the brain and received by the brain is actually quite a bit different when these same neurons are responding to artificial sweeteners versus actual sugar.”