Why Is a High Fiber Diet Prohibited Before a Colonoscopy?

A colonoscopy is something no one looks forward to but everyone has to endure at some point. Before your procedure, your doctor will give you colonoscopy prep instructions to follow, and these will make the colonoscopy easier and the results more accurate. Prep instructions include limiting your fiber intake a few days prior in order to empty your colon. If you don't follow these instructions, it could mean repeating or rescheduling your procedure.

Avoid fiber-rich foods, such as sweet potatoes, before a colonoscopy. (Image: Boyrcr420/iStock/GettyImages)

Tip

A high-fiber diet before a colonoscopy can affect the accuracy of your test results.

Non-Fiber Diet for Colonoscopy

High-fiber foods should normally be a part of your diet because they help improve colon health. But fiber can leave residue in your colon that can obscure your doctor's view of polyps and other issues. Polyps are small clumps of cells that may grow on the lining of your colon.

While most polyps are harmless, some can become cancerous. Your doctor will need to be able to see these, if they're present, to determine if they need to be examined further. That's why it's important to avoid fiber before your appointment.

Foods to Avoid Before Colonoscopy

To aid your doctor and ensure the accuracy of your results, you should avoid high-fiber foods two to three days before your procedure — or for however long your doctor recommends. In general, you should avoid beans, nuts, seeds, whole grains, raw fruits and vegetables, and dried fruits. Some examples of high-fiber foods to avoid include:

  • Raspberries
  • Pears
  • Strawberries
  • Apples
  • Peas
  • Broccoli
  • Brussels sprouts
  • Kale
  • Celery
  • Carrots
  • Lentils
  • Chickpeas
  • Black beans
  • Brown rice
  • Granola
  • Whole-grain bread
  • Almonds
  • Walnuts
  • Raisins

With your doctor's permission, you may be able to eat well-cooked or canned fruits and vegetables without skin, because they're softer and pass through your colon more easily. For example, you can eat:

  • Steamed or sauteed spinach
  • Boiled or roasted carrots
  • Baked apples without skin
  • Baked or mashed potatoes and sweet potatoes

You may also be able to eat refined grain foods and nut butters, including:

  • White rice
  • White pasta
  • White bread
  • Peanut butter

Always get your doctor's go-ahead before you eat a food you're not sure is allowed.

Day Before and Day of Diet

For at least 24 hours before your procedure, you will have to avoid solid foods altogether. During this period, you may have clear liquids such as water, clear broth or bouillon; coffee; tea; apple or white grape juice; clear soft drinks; sports drinks; flavored gelatin; and Popsicles.

Your doctor will provide you with a bowel-cleaning liquid to drink the afternoon and evening before your procedure. This is typically a large volume of liquid you drink at intervals — however, there are newer low-volume prep products you can ask your doctor about. These liquids induce diarrhea, so you will want to stay close to a bathroom.

Some patients report that the newer low-volume preparations are more palatable, while most agree that the larger-volume liquids can be very unappealing. To improve your experience, chill the prep and drink it when it's cold. You can also try adding a powdered drink mix for flavor, as long as the mix is not red or purple — these dyes can interfere with your colonoscopy results.

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