In order to determine whether failure of the colon to salvage carbohydrate could contribute to the diarrhoea of ulcerative colitis we investigated the effect of ingesting a drink containing 20 g lactulose on stool output and breath hydrogen production in 39 colitic patients subdivided according to their disease extent and activity and in 14 normal volunteers. Each subject took a standard diet for four days and stool output was monitored throughout this period. Administration of lactulose on day three significantly increased stool weight and frequency in patients with both active and quiescent total colitis (p<001), but not in patients with distal colitis or in the volunteers. The basal and peak breath hydrogen responses to ingested lactulose were similar to normal controls in all patient groups but the hydrogen concentration tended to be higher in colitics. The mouth to caecum transit of the lactulose meal was slower in all groups of colitics (p<0-02) when compared with controls. These results suggest that impaired colonic salvage of carbohydrate could contribute to the diarrhoea in patients with total colitis who are ingesting a diet rich in unabsorbed carbohydrate, or who are hypolactasic.
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