Colonoscopy is the best method for colon cancer screening and to evaluate bowel abnormalities, including cancer. However, good bowel preparation is essential for a successful colonoscopy. Several studies have shown Low Residue Diet (LRD) to be better tolerated without any negative effects on bowel cleansing compared to Clear Liquid Diet. Several studies have compared 1-day vs. 3-day LRD for bowel cleansing. This study aims to compare the impact of the duration of LRD for colonoscopy bowel cleansing in adult patients.


We studied the Cochrane and MEDLINE/Ovid databases from inception to November 2020 with keywords “colonoscopy,” “bowel preparation,” “bowel cleaning,” “1-day,” and “3-day”. Initially, 107 studies were identified, which were further screened with title and abstracts. Seven studies were selected for full-text review. Two studies were also excluded as one of them had included pediatric patients, and another was a post-doc analysis. Four studies were included in the final analysis.


All studies were single-institution studies conducted in Spain (2), Portugal (1), and Turkey (1) on elective patients only. Patients with significant comorbidities were excluded from all 4 studies, with 2 specifically excluding inflammatory bowel disease patients and one excluding patients with a history of poor bowel preparation in the past. Two studies included only morning colonoscopies, one from 8AM-4PM, and one did not specify the timing. Experienced endoscopists performed the procedure in 3 studies. All studies showed that 1-day LRD was not inferior to 3-day LRD to achieve adequate bowel cleansing, polyp detections, adenoma detection, and cecal intubations. Patients reported tolerating the 1-day LRD significantly better in 2 studies, with the other 2 showing equivalence between the groups (Table 1).


1-day LRD is not inferior to 3-day LRD for a select population of patients undergoing elective outpatient screening colonoscopies. However, there is no data to support or negate this finding in patients with significant comorbidities, specifically in patients with IBD who need serial screening colonoscopies. This group requires specific investigation in future studies.

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The American Journal of Gastroenterology