The success of a colonoscopy depends on preparation, which includes a dietary change in the days leading up to the procedure. This involves shifting to a low-fiber, or low-residue, diet to ensure the physician has a clear view of the colon’s lining. This diet reduces the amount of indigestible material passing through the gastrointestinal tract, making the final cleansing process more effective and helping prevent the need for a repeat procedure.
The Goal of Reducing Intestinal Residue
The primary reason for limiting fiber is to minimize “residue” in the colon—the parts of food that pass through the digestive system largely undigested. Fiber, especially the insoluble type, is not broken down by human enzymes and creates bulk in the stool. This undigested material can obscure polyps or other abnormalities.
A low-residue diet ensures that less solid matter reaches the large intestine. The goal is a completely clean colon for clear visualization. If too much residue remains, the procedure may be considered incomplete, potentially requiring a reschedule.
Acceptable Low-Residue Foods
The low-residue diet focuses on foods that are easily digested and absorbed.
Grains
For grains, the focus is on refined white products, which have had the fibrous bran and germ removed. Acceptable options include white bread, plain crackers, white pasta, and white rice (less than 0.5 grams of fiber per serving).
Protein and Dairy
Lean, tender, and well-cooked protein sources are preferred, such as skinless chicken, turkey, fish, and eggs. Dairy products are generally allowed in limited amounts, including milk, cheese, and smooth yogurt without seeds or fruit chunks.
Fruits and Vegetables
When consuming fruits and vegetables, all skins, seeds, and pulp must be removed, as these contain the highest concentration of fiber. Safe choices include:
- Strained fruit juices without pulp.
- Ripe bananas and melons.
- Canned fruits like peaches and apricots.
- Cooked vegetables without skins, such as peeled potatoes, well-cooked carrots, or asparagus tips.
Foods to Strictly Avoid
Consuming high-fiber foods must be eliminated from the diet during the preparatory phase. All whole grains, including brown rice, wild rice, oatmeal, whole-wheat bread, and high-fiber cereals, are forbidden. These foods create significant residue that is difficult to clear.
Nuts, seeds, and popcorn are particularly troublesome because their small, dense pieces can interfere with visualization. This restriction extends to foods containing them, such as seeded bread, granola bars, and certain baked goods.
High-residue fruits and vegetables must be excluded:
- All raw vegetables, especially those with stalks, skins, or peels (e.g., broccoli, corn, leafy greens).
- Fruits with tough skins or seeds (e.g., berries, oranges, and apples with skin).
Consumption of these items can lead to an inadequate bowel preparation.
Timeline for Dietary Changes
The low-residue diet is a short-term measure that begins a few days before the procedure, typically three to five days out. This initial phase allows the digestive system to start clearing food waste before the final cleansing begins.
The diet then transitions to a strictly clear liquid diet for the entire day immediately preceding the colonoscopy. This final phase eliminates all solid food and includes only liquids you can see through, such as water, clear broth, plain gelatin, and clear fruit juices without pulp. This clear liquid diet, combined with the prescribed laxative solution, ensures the colon is completely empty for the examination.