What it is
A rare sugar made by rearranging galactose from whey — near the sweetness and browning of real sugar, but most of it slips past digestion.
Why your biology objects
Only ~15–20% is absorbed; the rest ferments in the colon to short-chain fatty acids like a prebiotic, so its glycemic index is ~3. Benign at normal doses — the catch is the same as the polyols: enough of it draws water and causes gas. Not ancestral, but metabolically gentle.