Digestible foods. Before a colonoscopy, a person should only eat easily digested foods. These foods should be eaten during the 3 to 4 days before the colonoscopy. Foods like skinless potatoes, skinless chicken, cheese, white fish, clear soup, and eggs can all be consumed. A person should avoid eating red meat, fatty foods, as well as foods that are high in fiber. If a person eats a lot of high-fiber this could increase the amount of activity in the colon. This could affect the doctor’s ability to see the inside of the colon. Steer clear of high-fiber vegetables, whole-grain pasta, cereals, bran, seeds, and fruit.