Your doctor needs a clear view of your colon during a colonoscopy in order to spot precancerous growths, infections and other problems. So you’ll be asked to clear it out—by making sure all solids have exited your intestinal tract before your appointment. Called bowel prep, the process usually takes 1 to 2 days. You follow a clear liquid diet, then take a laxative or enema the night before your colon check. This whisks any stool that remains inside you out of your intestines, and usually makes staying home and close to a bathroom a necessity. Good bowel prep may not be enjoyable, but it is essential: In one study, doctors were able to spot twice as many precancerous polyps in clean bowels.

• Stop taking iron supplements several weeks before your colon check; iron makes stool black, which can block the view.
• Avoid drinks, frozen pops or gelatin containing red or purple dyes during bowel prep; these can stain colon walls, obscuring bleeding and trouble spots.
• In one study, great bowel prep reduced the number of colonoscopies that had to be stopped short and rescheduled by two-thirds.
• You’ll lose nearly three quarts of fluid during bowel prep. Drink plenty of water to prevent dehydration.
• If you’re on a low-salt diet, ask your doctor about low-sodium bowel prep products.

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