A successful colonoscopy depends heavily on proper bowel preparation, and the diet consumed two days before the procedure (Day -2) is a transitional stage. This day marks the beginning of strict dietary changes to prepare the body for the clear liquid diet required the following day. Undigested material remaining in the colon can obscure the lining, potentially causing the physician to miss polyps or other abnormalities. The goal is to minimize solid waste production, ensuring the colon is clean enough for a thorough and accurate examination.
The Goal of Low-Residue Eating
Two days before the procedure, the patient switches to a low-residue diet. This diet is specifically designed to reduce the volume and frequency of stool by limiting the amount of indigestible material left in the colon. “Residue” refers to the undigested parts of food, primarily dietary fiber, that pass through the small intestine. Fiber contributes significantly to stool bulk, which must be eliminated for the procedure. Avoiding high-fiber foods ensures the digestive tract has less to process, making the final bowel preparation solution more effective for high-quality visualization of the colon wall.
Allowed Foods
The foods permitted on Day -2 are refined, easily digestible items that leave behind minimal undigested material. Patients should focus on products made from white flour, which has had the fibrous bran and germ removed. Lean, tender protein sources are also allowed, as they are broken down almost completely in the digestive tract. Acceptable choices include:
- Refined grains, such as white rice, white bread, plain white pasta, and refined breakfast cereals like Cornflakes.
- Lean proteins, such as skinless chicken or turkey, lean beef, fish, and eggs (not fried).
- Dairy products, including milk, plain yogurt, cottage cheese, and cheese.
- Clarified fruit juices without pulp, clear broths, and gelatin (without red or purple dye).
Foods to Eliminate
Foods that must be eliminated on Day -2 are those high in fiber, hard-to-digest components, or those containing pigments that can stain the colon lining. These items are highly indigestible and can lodge in the colon, potentially blocking the scope or obscuring the view. Foods to avoid include:
- All whole grains, such as whole wheat bread, brown rice, oatmeal, or high-fiber cereals.
- Nuts, seeds, and popcorn, including small seeds found in berries, tomatoes, and chunky nut butters.
- All raw vegetables, most cooked vegetables, and fruits with skins or seeds (e.g., broccoli, corn, peas, and apples).
- Highly pigmented foods or drinks, particularly red, purple, or blue items, as their color can be mistaken for blood.