Lactulose (4-O-β-D-galactopyranosyl-D-fructose) is a synthetic disaccharide sweetener made by alkaline isomerisation of lactose, with about 1.5 times lactose’s sweetness and roughly half the calories of sucrose. Beyond food use as a mild, prebiotic sweetener in yoghurts and functional products, it is well known pharmaceutically as a gentle osmotic laxative and as a treatment for hepatic encephalopathy — feeding colonic bifidobacteria, which acidify the gut. Heat treatment of milk naturally forms small amounts via the Lobry de Bruyn–Alberda van Ekenstein transformation, and its level (by HPLC) can indicate how severely milk has been heated — a marker distinguishing pasteurised from UHT milk.