Participants who were allocated to the 2 L PEG with ascorbic acid (PEGA) group took 250 ml of PEG with ascorbic acid at 15-min intervals, completing 1 L of the PEG with ascorbic acid protocol at 8:00 PM on the day prior to the procedure. The remaining 1 L of the PEG with ascorbic acid solution was administered in the same manner at 6:00 AM on the day of the procedure. Participants assigned to the 1 L PEG with ascorbic acid with PLD (PLD) group consumed a prepackaged, low residue diet (ZeroCol, Korea Medical Food Inc., Seoul, Korea) which consisted of a breakfast, lunch and dinner, the day prior to colonoscopy. The Participants took 1 L PEG with ascorbic acid solution at 6:00 AM on the day of the colonoscopy in the same way as described above. All of the subjects ingested 500 mL of water for every 1 L of 1 L PEG with ascorbic acid solution consumed. The Participants completed all of the administrations at least 2 hours before the colonoscopy.

Definition: Achievement of preparation adequacy was defined by as having BBPS scores of 2 or 3 for all colon segments.

BBPS was measured by Physician who performing colonoscopy. To maintain precise evaluation, the physician participated in an online training program from www.cori.org/bbps. For each colon segment, BBPS preparation score ranged 0 to 3. Definition of BBPS are presented at www.cori.org/bbps

Tolerability and adverse events were measured by comprehensive questionnaire. Participants were asked about the presence of distressing symptoms, such as abdominal pain/discomfort or nausea/vomiting, and if they had problems taking the entire dose. The subjects also reported the percentage of the preparation they completed (100%, 90~99%, <90%), regardless of solution or meals. Adverse events are categorized by CTCAE v4.03.