ii. Primary goal: to achieve a reduction from 15 to 5% of inappropriate preparation result; The Boston Bowel Preparation Scale (BBPS) will be used as grading system. Inappropriate is defined as total BBPS < 6 or < 2 in any segment. The chosen scale is the most systematically validated and appropriate for the clinical setting. iii.Both groups, from a community-based outpatient ambulatory center, used the same split dose regimen with Polyethylene glycol (PEG).Patients were instructed to drink 3 L of PEG preparation on the afternoon of the day prior to the exam and 1 L four hours before the scheduled exam time. All the exams scheduled for morning period. Assuming a normal distribution, a power of 90% and a type I error of 0.05, the calculated sample size for each group was 188; allowing a 10% dropout rate, the sample size is 206 per group (412 patients overall); Groups: Group A: 3-day low residue diet + split dose preparation; Group B: 1-day low residue diet + split dose preparation