The small intestine's large capacity for glucoseabsorption and for adaptation seems to contradict thereported importance of carbohydrate malabsorption inshort bowel (SB) patients. The aim of the present study was to investigate the occurrence ofmalabsorption in these patients ingesting realisticamounts of carbohydrates. We performed a dose-responsestudy [ingestion of increasing amounts of glucose and complex carbohydrates (boiled rice and wheatbread), and the nonabsorbable disaccharide lactulose] inSB patients with an intact colon. The hydrogen(H2)-breath test and changes in serum acetate were used to evaluate colonic fermentation and,thus, indirectly, the lack of small intestinalcarbohydrate assimilation. Blood glucose and plasmainsulin were measured to evaluate absorption. Plasmaconcentrations of the ileal brake hormones —glucagon-like peptide-1 (GLP-1) and peptide tyrosinetyrosine (PYY) — were measured to test whetherrelease of these hormones was related to colonicfermentation. Significant amounts of 25 g and 50 g glucose, and of thebread and rice meals were fermented rather thanabsorbed, as judged by the increases in endexpiratoryH2. Serum acetate concentrations weresignificantly higher in SB patients than in healthy controls.The orocecal transit times of all test meals ranged from15 to 120 min. GLP-1 and PYY releases in SB patientswere significantly higher than in healthy volunteers. They were mutually parallel and paralleled theincrease in insulin. They were not related to ongoingfermentation or to intraluminal carbohydrate content perse, but most probably to absorption of glucose in the distal bowel. In conclusion,well-adapted SB patients had pronounced small intestinalmalabsorption of carbohydrate, even after ingestion ofsmall amounts of easily absorbable carbohydrates. A fast small intestinal spreading of carbohydrates,once in the small intestine, and a spill-over to thecolon seem to explain the data best.