Supplementary Material for: One-day versus three-day low residue diet and bowel preparation quality before colonoscopy: a multicenter, randomized, controlled trial

Background One-day low residue diet (LRD) is recommended before colonoscopy, but only three single center trials compared the 1-day vs 3-days LRD. The aim of this multicenter study was to compare the impact of a 3-days vs 1-day LRD on its ability to adequately and successfully prepare the bowel of outpatients that require a colonoscopy. The outpatients' tolerance and adherence to the LRD were also considered. Methods Consecutive outpatients were randomized to 1-day vs 3-days LRD at three open-access Endoscopy units. The primary endpoint consisted of the proportion of patients with a satisfactory degree of bowel cleanliness (Score 2-3 on the Boston Bowel Preparation Scale (BBPS) in each segment). Secondary endpoints were patients’tolerance and adherence to the prescribed diet evaluated by a standardized questionnaire. Results 289 patients were included in the study (1-day LRD arm=143, 3-days LRD arm=146). BBPS≥2 was not significantly different in the two dietary regimens in any of the three colonic segments (71%vs72%, p=0.9). The percentage of patients with incomplete preparation was similar in the two arms (9%vs9%; p=1.0). No significant differences were found among colonoscopy findings in terms of abnormalities (81%vs84%, p=0.8). Both groups scored similarly in overall tolerance to LRD (48%vs49%, p=1.0) and also in whether they would haveadopted a different dietary regimen(p=0.3). Conclusion Our multicenter randomized study confirmed that optimal bowel cleansing is reached through a 1-day LRD.