Previously, our team compared the effects of a low-residue full nutrition formula podwer (FNFP) combined with 3 liters of polyethylene glycol(PEG) solution and the self-prepared low-residue diet combined with 3 liters of PEG solution on the quality of bowel preparation for colonoscopy, and the results showed that the adequate bowel preparation rate was significantly improved in low-residue full nutrition formula podwer group. However, there are still a considerable number of patients in the process of taking 3L PEG appeared bloating, abdominal pain, nausea, vomiting and other adverse reactions, indicating some subjects can not tolerate the dosage of 3L PEG. In order to reduce adverse reactions and provide more options for people with low PEG tolerance, this study intends to compare the effects of low-residue FNFP combined with 2L PEG and self-provided low-residue diet combined with 3L PEG on the quality bowel preparation, colonoscopy lesions detection, adverse reactions, and tolerance, compliance and satisfaction of subjects.

Inclusion Criteria:

• adult subjects between the ages of 18 and 75 who were scheduled for screening, monitoring, and diagnostic colonoscopy.

Exclusion Criteria:

• severe heart, brain, lung, kidney complications or a history of acute myocardial infarction within six months.
• a history of abdominal or pelvic surgery, BMI > 28 or BMI < 18.5, inflammatory bowel disease, constipation (less than 3 bowel movements in the past week, with strenuous bowel movements, hard stool, small volume), or intestinal obstruction.
• imaging and laboratory tests are highly suspicious of colorectal cancer or warning signs and symptoms of colorectal cancer: blood in the stool, black stool, unexplained anemia and significant weight loss, abdominal mass, and positive digital rectal examination.