Preparing for a colonoscopy involves completely emptying the bowel through dietary changes one to two days before the procedure and using an agent that causes diarrhea, according to Harvard Medical School. The exact instructions for preparing for a colonoscopy vary depending on the medical center performing the procedure.
Dietary changes include reducing fiber a few days before the colonoscopy and staying on a clear liquid diet one day before and the day of the procedure, according to Harvard Medical School. A clear liquid diet includes foods such as broth, gelatin, popsicles, fruit juices, black coffee, tea, soft drinks, Gatorade and other clear drinks such as water and lemonade, as listed by Norton Healthcare. No red or purple dyes, dairy products, or acidic juices are allowed.
The particular laxative prescribed to clear the bowels depends on the doctor's preferences, the time the procedure is scheduled and the patient's past experiences, states Harvard Medical School. The use of the laxative involves several hours of diarrhea, requiring the patient to stay near or in the bathroom.
Completely clearing the bowel is essential so that the intestinal walls are accurately seen during the procedure, according to WebMD. Enemas may be administered before the procedure. Not completely emptying the bowels may mean polyps and lesions are overlooked, or that the entire procedure may need to be repeated, states Harvard Medical School.