Adequate bowel preparation is essential for full visualization of colonic mucosa because detection of small polyps and neoplasms depends on the quality of bowel cleansing. The aims of this study were to compare the efficacy, tolerability of preparation and side effect between two groups: clear-liquid diet with polyethylene glycol (PEG) solution versus no diet restriction with PEG solution.

This was a randomized single-blind prospective study. A total of 330 patients were randomly assigned to receive either 2 L PEG solution with a clear-liquid diet on the day before colonoscopy and another 2 L PEG solution on the day of the procedure (group 1) or 2 L PEG solution with a general diet on the day before colonoscopy and another 2 L PEG solution on the day of the procedure (group 2).

162 patients were assigned to group 1 and 168 patients to group 2. The satisfactory quality of bowel preparation was not significantly different between the two groups (80.2%, 78.6%, P =0.707). Patient's compliance of the clear-liquid diet in group 1 was 50%. The satisfactory quality of bowel preparation was weakly better when the clear-liquid diet was given 2 or 3 times a day (group 1A) than 0 or once a day (group 1B) (74.1%, 86.4%, P =0.048). The tolerability of the PEG solution and side effects of preparation were not significantly different in the two groups ( P =0.573, 0.686).

Bowel preparation with no diet restriction and split-dose PEG solution was similar to preparation with a clear-liquid diet in efficacy, tolerability and side effect. Therefore, the use of the clear-liquid diet protocol should improve patient's compliance.