The purpose of this study was to determine whether energy from malabsorbed carbohydrate could be conserved through colonic fermentation in short bowel syndrome. Seven patients with short bowel anastomosed to the remaining colon and five patients with short bowel without a colon were selected from the home total parenteral nutrition (TPN) program. Six normal volunteers also were studied. After an overnight fast, subjects consumed a 50-g carbohydrate bread meal and were studied hourly over the next 6 h. Carbohydrate malabsorption, estimated by lactulose breath hydrogen testing, was 48 +/- 13% in short bowel patients. After the bread meal, breath hydrogen was higher in short bowels with colons (69 +/- 20 ppm) than in either short bowels without colons (11 +/- 7 ppm) or normal subjects (10 +/- 3 ppm) (p less than 0.01). Blood acetate levels also were higher in short bowels with colons than in those without colons, reaching a peak of 167 +/- 27 mumol/L at 4 h (p less than 0.05). We conclude that in patients with a short bowel and a colon, malabsorbed carbohydrate is fermented and there is a rise in blood acetate, suggesting that the colon has a role in salvaging malabsorbed carbohydrate as a source of energy through carbohydrate fermentation.