Bowel preparation for colonoscopy: is diet restriction necessary?

Background: Bowel preparation is essential for quality colonoscopy. Although most bowel preparation regimens recommend dietary restriction for 24 to 48 hours before the procedure, the evidence for this is poor. This study aimed to investigate whether dietary restriction during bowel preparation improves the quality of colonoscopy. Methods: A prospective, randomised controlled pilot study in which the dietary restriction (DR) group (control) was instructed not to ingest high fibre foods for 48 hours prior to the use of a polyethylene glycol (PEG) bowel preparation. The non-dietary restriction (NDR) group were given no dietary instruction but received instructions for the use of the PEG-based preparation. On the day of colonoscopy, the quality of the bowel effluent was assessed, and additional preparation given as necessary. The primary endpoint was quality of bowel cleansing using the Harefield Cleansing Scale during colonoscopy. The secondary endpoints were the need for additional bowel preparation and the quantity of additional bowel preparation given prior to endoscopy. Data were analysed on an intention to treat basis. Results: Twenty-three participants were randomised to the intervention group and thirty-four to the control group. Patient demographics were similar in both groups. Dietary restriction did not influence the success rate of bowel preparation: 97% successful bowel preparation in the DR group, vs 91% successful bowel preparation in the NDR group (p = 0.559). Additional bowel preparation requirement were similar in both groups: 35% in the DR group vs 39% in the NDR group (p = 0.768). Mean amount of additional bowel preparation required was similar: 560 ml in the DR group vs 460 ml in the NDR group (p = 0.633). Conclusion: The quality of bowel preparation was comparable in patients with and without dietary restrictions prior to colonoscopy. Non-restrictive diets prior to bowel preparation should be considered to increase compliance. The sample size of this pilot study prohibited definite statistical conclusions but demonstrated this to be a reasonable methodology for a larger study.