Impact of Milk Consumption the Day Before Colonoscopy on Bowel Preparation Quality: A Randomized Controlled Trial

Dietary restrictions are critical for effective bowel preparation before colonoscopy. Milk has traditionally been considered to impair the quality of bowel preparation, and endoscopy centers commonly advise patients to avoid milk consumption prior to the procedure. However, no robust evidence currently supports this practice. We investigated whether milk intake affects bowel preparation quality and colonoscopy outcomes.

This prospective randomized controlled trial enrolled patients undergoing colonoscopy, randomizing them into either milk-inclusive low-residue diet group (Milk group) or standard low-residue diet group (LRD group). The primary outcome was the bowel preparation adequacy rate, evaluated using the Boston Bowel Preparation Scale. The secondary outcomes included colonoscopy quality metrics (polyp detection rate, adenoma detection rate, BBPS score, and cecal intubation rate), patient tolerability, participant preferences, and adverse event incidence.

A total of 486 participants were randomly allocated to two groups. Non-inferiority of the Milk group to the LRD group was demonstrated, as the lower limits of the one-sided 97.5% confidence intervals for the difference in adequate bowel preparation rates (mITT: - 0.6%; PPS: - 1.7%) were both above the - 10% margin. Bowel preparation quality was slightly higher in the Milk group than in the LRD group ( mITT: P = 0.049; PPS: P = 0.030). The incidence rate of nausea (21.2 vs. 30.1%, P = 0.046) was lower in the Milk group than those in the LRD group, and the satisfaction scores (3.79 ± 0.86 vs. 3.61 ± 0.84, P = 0.005) were higher in the Milk group. No significant differences were observed in polyp and adenoma detection rates between the two groups.

During colonoscopy preparation, milk-inclusive low-residue diet is non-inferior to a standard LRD for bowel preparation and is associated with better patient-reported tolerability. Allowing milk consumption on the day before colonoscopy is a safe and patient-friendly strategy that can be adopted to enhance comfort without compromising the quality of the examination.

ChiCTR2500103886, Registration date: 06 June 2025 (retrospectively registered).