A low-residue diet (LRD) is recommended as part of bowel preparation before a colonoscopy. However, the optimal duration of the LRD is unclear. A retrospective cross-sectional study was therefore conducted at E-Da Dachang Hospital. We compared bowel preparations using the Aronchick score and other quality metrics during two consecutive periods: May 2019 to December 2019 (3-day LRD) and January 2020 to August 2020 (1-day LRD). A total of 2823 patients were enrolled (1592 in the 3-day LRD group and 1231 in the 1-day LRD group). The most common bowel cleansing agent was sodium picosulfate and magnesium citrate (SPMC, 84.2%), followed by polyethylene glycol (PEG, 10.0%) and sodium phosphate (5.8%). Compared with patients in the 3-day LRD group, patients in the 1-day LRD group had higher SPMC use (88.1% vs 81.3%, P < .001) and supplemental laxative use (25.9% vs 19.3%, P < .001).The proportion of adequate bowel preparation (84.2% vs 85.1%, P = .563), cecal intubation rate, adenoma detection rate, and right-side adenoma detection rate were not significantly different between 1-day LRD and 3-day LRD groups. More advanced adenomas (5.9% vs 3.4%, P = .002) and sessile serrated lesions (8.9% vs 6.3%, P = .014) were observed in the 1-day LRD group. In addition, the types of laxatives (SPMC, sodium phosphate, and PEG) and the use of supplemental laxatives did not affect bowel preparation scores. In conclusion, a 1-day LRD led to bowel preparation similar to that achieved through a 3-day LRD regardless of the type of primary cleansing agent or the use of supplemental laxatives.