A colonoscopy allows a physician to examine the lining of the large intestine for polyps and other abnormalities. For the procedure to be accurate, the colon must be completely clean, requiring a process known as bowel cleansing. This involves laxatives and strict dietary restrictions beginning several days beforehand. These limitations eliminate residual matter that could obstruct the view of the intestinal wall, ensuring a high-quality examination.
The 5-Day Rule: Eliminating High-Fiber Foods
The primary restriction beginning five days before your procedure is the elimination of high-fiber, or high-residue, foods. These items are restricted because they are resistant to digestion and can leave behind undigested particles that cling to the colon wall, obscuring polyps or lesions. You must stop eating all nuts and seeds, including tiny seeds found in items like strawberries, raspberries, and seedy bread or dressings. Popcorn should also be strictly avoided during this period.
Any food containing whole grains must be removed from the diet, including whole wheat bread, brown rice, wild rice, and oatmeal. This restriction also applies to raw fruits and vegetables, especially those with skins or tough peels, such as apples, corn, and broccoli. Eliminating this tough, fibrous material early makes the final cleansing phase much more effective. Failure to adhere to this five-day rule is the most common reason a colonoscopy must be rescheduled.
Acceptable Foods During the Restricted Period
During the five-day period, the goal is to shift to a low-residue diet, focusing on foods that are easily digested. Patients should choose refined carbohydrates, such as white rice, white bread, plain pasta, and low-fiber cereals like corn flakes or puffed rice. These items contain minimal fiber and leave little residue in the colon.
Lean, tender protein sources are encouraged, including skinless chicken, fish, eggs, and tofu, as these provide necessary calories and nutrients. If consuming fruits and vegetables, they must be completely peeled, well-cooked, and seedless, such as peeled potatoes, canned peaches, or bananas. Clear, light-colored liquids like water and apple juice should also be consumed freely to maintain hydration.
Transitioning to the Clear Liquid Diet
The low-residue diet must transition completely to a clear liquid diet, typically beginning 24 hours before the scheduled colonoscopy. All solid food must be stopped, and the only acceptable intake includes transparent liquids that leave virtually no residue in the colon. Approved options include:
- Clear broth (chicken or beef)
- Gelatin
- Clear sodas
- Pulp-free juices like white grape or apple
- Plain water
Black coffee or tea is also permitted, but no milk, cream, or non-dairy creamers can be added, as dairy is not considered a clear liquid.
A strict warning applies to all liquids and food items, which must not contain any red, blue, or purple dyes. These artificial colorings can mimic the appearance of blood or stain the lining of the colon, which can interfere with the physician’s ability to accurately detect abnormalities during the examination.
Medications and Supplements to Avoid
Patients must consult their prescribing doctor about temporarily stopping blood-thinning medications, which may increase the risk of bleeding if a polyp is removed during the procedure. Iron supplements must also typically be discontinued seven days before the colonoscopy, as they can darken the stool and impair visibility.