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  2. Preparing for a Colonoscopy

Preparing for a Colonoscopy

  1. What is a colonoscopy?
  2. Initial preparations
  3. Diet
  4. Cleansing the bowel
  5. FAQ

What is a colonoscopy?

A colonoscopy involves inserting a thin, flexible tube called a colonoscope into the body through the anus to examine the colon and rectum. The main purpose of a colonoscopy is to investigate symptoms which may be coming from the bowel, such as:

  • Abdominal pain
  • Constipation
  • Passing blood with bowel movements.
  • Persistent diarrhoea

During a colonoscopy it is possible to identify growths (including non-cancerous polyps and colon cancers), bleeding, and areas of inflammation. It is necessary for the whole bowel to be visible to the video camera on the end of the colonoscope, otherwise it is impossible to carry out this screening process effectively.

Preparing for a colonoscopy consists of following a diet and activity plan (colonoscopy prep). The aim of colonoscopy prep is to ensure that the colon is empty and clean before the procedure. This normally involves following a diet plan with low fiber food, drinking bowel-cleaning liquids and can also require the use of enemas in cases where it is difficult to empty, due to constipation.

Initial preparations

Everybody who prepares for a colonoscopy experiences frequent bowel movements as the diet plan and laxative medications take effect, and will need ready access to a bathroom. For this reason, clearing one’s schedule of appointments for two days before the procedure and staying at home are both highly recommended.

Before starting colonoscopy prep, most people find it helpful to shop for all the supplies that they will need. In addition to the foods and liquids that will be eaten as part of the diet plan, people preparing for a colonoscopy may wish to purchase products to soothe the skin around the anus, specifically diaper cream (to soothe the skin) and alcohol-free cleansing wipes containing aloe-vera or vitamin E.

Colonoscopies are an outpatient procedure in most cases. However, people undergoing a colonoscopy are usually given sedatives to help them relax and to ensure that they are comfortable during the procedure. In all cases where sedatives are used, it is advisable for the person undergoing the procedure to arrange for a friend or family member to accompany them to and from the hospital.

Diet for colonoscopy prep

During colonoscopy prep, one should aim to eat a diet which is nutritious, but which does not cause large amounts of feces to form in the intestine. Three days before the procedure, it is important to stop taking fiber supplement products, as these help the body to produce fecal matter and would work against the colonoscopy prep diet.

At this point, it is important to stop taking supplements and vitamins as well as any medicines that contain iron.[1] The doctor will advise on whether and when to stop taking any prescription medicines that are normally used regularly, and on the use of over-the-counter anti-inflammatory medications, such as ibuprofen.

Low fiber food

Eating a diet of low-fiber food for three or four days before the procedure will help to empty the bowel, because low-fiber foods are easy to digest and leave one’s system quickly.

Foods to avoid during colonoscopy prep include:

  • Fatty foods
  • Fruit with seeds or peel such as apples, berries or figs
  • High-fibre cereals such as bran flakes or granola
  • High-fibre vegetables such as corn, broccoli, cabbage, beans or peas
  • Legumes such as dried peas, lentils or split peas
  • Seeds, nuts or popcorn
  • Tough meat with gristle
  • Raw vegetables
  • Whole grains

Low-fibre foods which are suitable for a colonoscopy prep diet plan include:

  • Cooked vegetables without skin or peel
  • Eggs
  • Fish
  • Fruit without skin or seeds
  • Lean meat such as chicken, turkey or veal
  • Well-cooked vegetables without skin
  • Breads and cakes made with refined white flour such as bagels, muffins or rolls
  • Pasta and rice
  • Potatoes without skin
  • Smooth peanut butter or almond butter

Avoid solids

The day before before the colonoscopy procedure, the doctor will recommend avoiding solid food completely. Following a liquid-only diet for this time period helps prevent new fecal matter from forming and entering the area which will be examined during the screening, which will ensure that it remains empty and clean. It is important to avoid red and purple food dyes[2] as they can discolor the lining of the colon and make it harder for the doctor to see the area being examined during the colonoscopy.

Drinks and liquid foods which are suitable to eat the day before the procedure include:

  • Clear broth including chicken, beef, or vegetable
  • Clear, light-colored juices such as apple, white grape, lemonade without pulp, and white cranberry
  • Flavored water
  • Jell-O or other gelatin without fruit (taking care to avoid red and purple food colouring)
  • Popsicles without fruit or cream
  • Water
  • Soda
  • Sports drinks such as Gatorade and Propel (light colors only)
  • Tea and black coffee without any cream, milk or sweetener

Cleansing the bowel

The aim of colonoscopy prep is to pass all the fecal matter from the area to be examined during the screening, so that there is nothing left to obstruct the view of the colonoscope. Many people pass clear, yellow liquid once they have finished passing waste. This liquid is made up of digestive juices and does not indicate that the prep has been ineffective. However, if the person preparing for the colonoscopy is still passing liquid containing fecal matter, or brown, cloudy liquid, they should consult their doctor as they will need to take additional steps to clean their colorectal region before the procedure can be performed.

To aid the process of emptying the bowel, one will be prescribed a laxative product to take as part of the colonoscopy prep. In some cases, the doctor will also prescribe enemas.

Laxative products

A laxative is a medication which helps the stool to pass smoothly through the colon. Before a colonoscopy, doctors most commonly prescribe osmotic laxatives, which work to empty the bowel by drawing the water from the large intestine into the stool in order to soften it, making it easier to pass.

Osmotic laxatives are usually drunk dissolved in large amounts of water. Specific instructions for preparing the laxative solution vary from brand to brand, and will found be on the packet of the laxative product that has been prescribed. Call the doctor if there is any confusion about how to prepare the solution and when to take it. Because osmotic laxatives work by keeping water in the bowel, it is important to drink enough liquid to stay hydrated. Drink water, or one of the recommended liquids, regularly throughout the colonoscopy prep plan.

It is possible for laxative products to make one feel nauseous. To avoid nausea, sip the laxative solution rather than drinking it slowly, and use a straw. To avoid vomiting, it can also be helpful to leave longer intervals between drinks. If someone does vomit after consuming a dose of the laxative solution during their colonoscopy prep, it is important to repeat the dose.


In some cases, following the diet plan and using laxatives are sufficient to empty the bowel. However, some people, particularly those who are suffering from constipation, may need additional assistance to empty the bowel before their colonoscopy. In these cases, the doctor will prescribe an enema.

The type of enema which is incorporated into colonoscopy prep is called a cleansing enema. It involves injecting liquid into the bowel via the rectum. This helps the body to push out any remaining waste. The liquid which will be used is usually a water-based solution with a small concentration of stool softener. The volume of water stimulates the movement of the large intestine, which in turn stimulates the bowels to expel both the solution and any remaining fecal matter.

If the bowel is not completely cleansed following an enema, the process can be repeated one or two more times. It is possible to undergo an enema in hospital, or to purchase an enema kit to carry out this process at home. The doctor will identify the most suitable option for the individual undergoing the procedure.

Colonoscopy preparation FAQs

Q: What should I do if the colonoscopy prep isn’t working?
A: The purpose of colonoscopy prep is to remove all fecal matter from the bowel. If a person usually suffers from constipation or chronic constipation, they may need an extended prep period before their colonoscopy procedure. It is helpful to discuss constipation issues with the doctor when planning a colonoscopy, so that the preparation time can be adjusted if needed. An extended preparation period typically involves the use of enemas and doubling the colonoscopy prep time-frame (two days spent eating low-fiber food, and two days of following the liquids-only diet).

Q: Can I take routine medications whilst I am following my colonoscopy prep plan?
A: In the run up to a colonoscopy, a person should take their routine medication as normal. On the day of the procedure, if one is scheduled for a morning procedure, avoid taking any medication unless specified by the doctor, with the exception of blood pressure, heart and seizure medication. If a colonoscopy is scheduled for the afternoon, a person may take their routine medication, other than medications that they were instructed to avoid. Pain medication should not be taken within six hours of any procedure.

Q: What can I do to reduce feelings of hunger during my colonoscopy prep?
A: It is normal to feel hungry whilst following the colonoscopy prep diet, particularly in the liquid-only stage. It is important to follow the diet plan in order to ensure that the prep is effective. Drinking sodas with a high sugar content can help to keep feelings of hunger at a minimum during this stage. Feelings of hunger should not be a cause for concern; however, if one experiences pain as a result of the hunger, consult the doctor who will be able to recommend appropriate painkillers.

  1. Diet Advice and Bowel Preparation (Bowel Prep) for Your Colonoscopy.” Guys and St. Thomas's NHS Foundation Trust. November 2014.

  2. How to Prepare for Your Colonoscopy.” Gastroentrology Center of Connecticut, PC. May 2017.