Before the colonoscopy, the doctor will give the patient some medication to cleanse the stool in the intestine so that the stool in the colon and rectum can be emptied and the intestinal cavity can be better viewed through the colonoscope. Therefore, foods that can interfere with the emptying of feces or tend to remain in the intestinal tract should be eaten sparingly. The following foods or foods with similar effects should be avoided three days before the examination: foods containing longer fibers, such as uncut vegetable leaves; seeds of various fruits, such as grape seeds; and watermelon, which some people like to eat in large quantities in summer instead of a meal, the flesh and seeds of which may remain in the intestine and not be easily excreted. The common feature of these foods is that they are not digested and have a light texture, and it is difficult to remove them all at once in a short period of time by taking laxatives. In addition, patients with severe constipation should explain the situation to the doctor before the examination, because such patients sometimes have difficulty in emptying their intestines by taking laxatives once or twice, and need to adjust their diet and take laxatives several times in advance in order to meet the examination criteria.