Carbohydrate malabsorption and the effect of dietary restriction on symptoms of irritable bowel syndrome and functional bowel complaints

Background: Carbohydrate malabsorption of lactose, fructose and sorbitol ha s already been described in normal volunteers and in patients with function al bowel complaints including irritable bowel syndrome. Elimination of the offending sugar(s) should result in clinical improvement. Objective: To examine the importance of carbohydrate malabsorption in outpa tients previously diagnosed as having functional bowel disorders, and to es timate the degree of clinical improvement following dietary restriction of the malabsorbed sugar(s). Methods: A cohort of 239 patients defined as functional bowel complaints wa s divided into a group of 94 patients who met the Rome criteria for irritab le bowel syndrome and a second group of 145 patients who did not fulfill th ese criteria and were defined as functional complaints. Lactose (18 g), fru ctose (25 g) and a mixture of fructose (25 g) plus sorbitol (5 g) solutions were administered at weekly intervals. End-expiratory hydrogen and methane breath samples were collected at 30 minute intervals for 4 hours. Incomple te absorption was defined as an increment in breath hydrogen of at least 20 ppm, or its equivalent in methane of at least 5 ppm. All patients received a diet without the offending sugar(s) for one month. Results: Only 7% of patients with IBS and 8% of patients with FC absorbed a ll three sugars normally. The frequency of isolated lactose malabsorption w as 16% and 12% respectively. The association of lactose and fructose-sorbit ol malabsorption occurred in 61% of both patient groups. The frequency of s ugar malabsorption among patients in both groups was 78% for lactose malabs orption (IBS 82%, FC 75%), 44% for fructose malabsorption and 73% for fruct ose-sorbitol malabsorption (IBS 70%, FC 75%). A marked improvement occurred in 56% of IBS and 60% of FC patients following dietary restriction. The hu mber of symptoms decreased significantly in both groups (P < 0.01) and corr elated with the improvement index (IBS P < 0.05, FC P < 0.025). Conclusions: Combined sugar malabsorption patterns are common in functional bowel disorders and may contribute to symptomatology in most patients. Die tary restriction of the offending sugar(s) should be implemented before the institution of drug therapy.