Passage of carbohydrate into the colon. Direct measurements in humans.

To quantify passage of unabsorbed dietary starch into the colon, 7 healthy volunteers had a multilumen tube positioned close to the ileocecal junction. Marker solution was perfused slowly, 20-40 cm above an aspiration site, to estimate, by marker dilution, flow through the ileum. On consecutive days, subjects ate liquidized meals containing 20 or 60 g starch; ileal aspirates were analyzed for starch and glucose for 5-6 h fasting and 4-7 h postprandially. Volume and carbohydrate concentrations were used to derive total carbohydrate traversing the ileum. In different subjects, unabsorbed carbohydrate was 453-4023 mg (2.3%-20.1%, mean 9.3%) for the smaller meal and 1332-6352 mg (2.2%-10.4%, mean 6.0%) for the larger. In 4 volunteers, hydrogen breath tests were performed on separate occasions after sucrose (50 g), lactulose (26 g), and the 20-g meal. Lactulose increased hydrogen excretion; sucrose and the test meal did not. We conclude that 2%-20% of dietary starch escapes absorption in the small bowel, confirming others' results using breath tests alone. Breath tests, though more convenient than intubation studies, may be a less sensitive index of starch malabsorption.