OBJECTIVES: To determine and compare the gastrointestinal (GI) responses of young adults following consumption of 45 g sucrose, 20, 35 and 50 g xylitol or erythritol given as a single oral, bolus dose in a liquid. DESIGN: The study was a randomized, double-blind, placebo-controlled study. SUBJECTS: Seventy healthy adult volunteers aged 18-24 years were recruited from the student population of the University of Salford. Sixty-four subjects completed the study. INTERVENTIONS: Subjects consumed at home without supervision and in random order, either 45 g sucrose or 20, 35 and 50 g erythritol or xylitol in water on individual test days, while maintaining their normal diet. Test days were separated by 7-day washout periods. Subjects reported the prevalence and magnitude of flatulence, borborygmi, bloating, colic, bowel movements and the passage of faeces of an abnormally watery consistency. RESULTS: Compared with 45 g sucrose, consumption of a single oral, bolus dose of 50 g xylitol in water significantly increased the number of subjects reporting nausea (P<0.01), bloating (P<0.05), borborygmi (P<0.005), colic (P<0.05), watery faeces (P<0.05) and total bowel movement frequency (P<0.01). Also 35 g of xylitol increased significantly bowel movement frequency to pass watery faeces (P<0.05). In contrast, 50 g erythritol only significantly increased the number of subjects reporting nausea (P<0.01) and borborygmi (P<0.05). Lower doses of 20 and 35 g erythritol did not provoke a significant increase in GI symptoms. At all levels of intake, xylitol produced significantly more watery faeces than erythritol: resp. 50 g xylitol vs 35 g erythritol (P<0.001), 50 g xylitol vs 20 g erythritol (P<0.001) and 35 g xylitol vs 20 g erythritol (P<0.05). CONCLUSIONS: When consumed in water, 35 and 50 g xylitol was associated with significant intestinal symptom scores and watery faeces, compared to the sucrose control, whereas at all levels studied erythritol scored significantly less symptoms. Consumption of 20 and 35 g erythritol by healthy volunteers, in a liquid, is tolerated well, without any symptoms. At the highest level of erythritol intake (50 g), only a significant increase in borborygmi and nausea was observed, whereas xylitol intake at this level induced a significant increase in watery faeces.