Colonoscopy is one of the most common methods for the diagnosis and treatment of lower gastrointestinal tract diseases and provides a unique opportunity to identify early neoplastic lesions.

Adequate bowel preparation is important for optimal colonoscopy. New bowel-cleansing regimens, study of patient-related risk factors to fail a proper preparation and diet adaptations have been studied recently.

A low residue diet is the standard in the day before the colonoscopy. Some endoscopists prescribe this dietary plan for a 3-day period prior to the exam, although no study compared the recommended 1-day versus 3-day diet regime, or the influence in bowel preparation results.

The aim of this project is to determine if the use of a 3-day low residue diet improves bowel preparations results and the influence in patient tolerability and adherence.

a. Study type: prospective, randomized, single-blinded trial:

i. Prospective inclusion of ambulatory patients;

ii. Randomization by computer generated tables;

iii. Allocation concealment by sealed, opaque envelopes;

iv. Patient not blinded to diet;

v. Endoscopist blinded to the diet followed by each patient.

b. Patient selection: Consecutive series of patients scheduled for total colonoscopy; Exclusion criteria: inpatients, sedation, urgent procedures, colonoscopies not intended to reach the caecum, patient with previous partial colectomy.

c. Sample Size:

i. 412 individuals; 2 groups of 206 patients

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

d. Endoscopist:

Exams to be conduct by 5 board-certified gastroenterologists and 2 supervised fellows in training; All physicians were trained in the use of BBPS by online training available at http://cori.org/bbps/, and have been using the BBPS for at least 3 months.

e. Data collection methods: form sheet filled by the endoscopist and patient opinion regarding the assigned bowel preparation protocol.

f. Analyzed variables:

i. Primary outcome: BBPS score

ii. Secondary outcome: Patient assessment of tolerance and acceptance of the preparation and diet

iii. Tertiary outcome: polyp detection rate (PDR), polyp location, size and configuration; adenoma detection rate (ADR), cecum intubation rate

iv. Other variables and patients characteristics (age, gender, chronic medication, risk factors for inappropriate preparation), withdrawal time.

g. Statistical analysis: T-test for groups comparing quantitative variables with normal distribution (primary outcome); Qui square test for groups comparing proportions (secondary and tertiary outcomes)

Inclusion Criteria:

• Consecutive series of patients scheduled for total colonoscopy
• Signed informed consent

Exclusion Criteria:

• inpatients
• sedation
• urgent procedures
• colonoscopies not intended to reach the caecum
• patient with previous partial colectomy.