BACKGROUND: Aims conventional bowel preparation restricts dietary intake up to 72 h prior to colonoscopy. Bowel preparation process is often perceived as unpleasant leading to poor compliance and subsequent poor bowel preparation. The aim of this trial is to compare the efficacy of low-residue semi-elemental enteral formula (LREF) incorporated diet versus the standard diet in polyethylene glycol (PEG)-based bowel preparation in the aim of creating a more tolerable bowel preparation regimen without compromising bowel cleanliness. METHODS: This was a multicenter, prospective, single-blinded, randomized controlled noninferiority trial. The noninferiority margin was set at 15%. One hundred sixty-seven patients were recruited and randomized to either the LREF group or the standard diet (SD) group using a 3L PEG preparation regimen. RESULTS: The LREF group results in comparable satisfactory preparation rating to the standard diet group with a mean BPPS score of 6.87 (SD 1.59) versus 7.14 (SD 1.54) (95% CI[-0.86
0.32] and p = 0.367). The mean difference (MD) of the BBPS total score between the two groups was -0.27 (95% CI [-0.764 and 0.224]). Equivalence were demonstrated using the two one-sided test (alpha = 5%) with the lower t-value of 2.682 (p = 0.0042) and the upper t-value of -4.493 (p <
0.01). There was also no significant difference in PEG compliance, willingness to repeat the procedure and tolerance to the bowel preparation between the two groups. CONCLUSION: The LREF incorporated diet is equivalent to regimen in achieving satisfactory bowel cleanliness in patients undergoing PEG-based bowel preparation. We suggest that a LREF incorporated regimen for bowel preparation can be considered in patients who are unable to sustain prolonged fasting to improve the procedural experience.