For a colonoscopy, patients need to fast, and for 3 days before the examination, they should abstain from eating foods rich in coarse fiber and eat a light diet. Not only fasting, but the patient also needs to cleanse the bowels. By drinking laxatives, the stool is expelled from the anal canal, rectum and colon to ensure that the intestines are empty so that the results of the examination are not affected by residual stool in the intestines. Usually, the colonoscopy can only be performed after fasting and preparing the bowel for cleansing, so that the mucosal tissues inside the intestine can be successfully observed for pathological changes such as congestion, edema, erosion, and the growth of polyps or tumors. Through the colonoscopy, the doctor can accurately determine the patient’s disease, so as to develop a suitable treatment plan and avoid the possibility of serious lesions or delayed disease. After the patient clears the bowel on an empty stomach, in addition to facilitating the examination, it also facilitates the treatment, such as the removal of polyps in the case of intestinal polyps, which can be performed by colonoscopy. If the patient is not prepared to fast and cleanse the intestine, it will cause the colonoscope to enter the intestine and the observation field is poor due to the accumulation of feces, which may not be able to detect the disease in time and may easily lead to missed diagnosis and misdiagnosis. In addition, incomplete bowel cleansing may cause damage to the colonoscope lens. Therefore, for the sake of their own health and the integrity of the colonoscopy equipment, patients need to fast and cleanse their bowels before colonoscopy.