Getting ready for a colonoscopy takes longer than the procedure itself, as Harvard Health Publishing points out — and that's largely because of all the dietary do's and don'ts you have to follow. Some of the instructions are focused on what you should eat — but even more of them are about what foods you should avoid before a colonoscopy.
After all, the whole goal of colonoscopy preparation is to empty your intestines so the doctor will be able to see any abnormalities when they go in with the colonoscope.
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"Emptying increases visibility," says Cordialis Msora-Kasago, RDN, a spokesperson for the Academy of Nutrition and Dietetics. "It allows your doctor to see the lining of your colon more clearly — and it also decreases complications." If the doctor can't see the lining of the intestine clearly, they could make a mistake such as inadvertently nicking it.
Preparing for a Colonoscopy
Fortunately, you should receive plenty of guidance from your physician ahead of the procedure. "Most people who are going to have a colonoscopy will receive instructions on what to do and will be offered a dietary protocol to follow," says Ruth Kander, RD a dietitian at The Fleet Street Clinic.
Different facilities have different guidelines when it comes to emptying the colon pre-procedure. "Colonoscopy prep and diet vary," says Msora-Kasago. "It's very important for individuals to follow the guidelines of their physician at the particular site they're going to."
That said, here's what you're likely to read in the instructions when it comes to the foods to avoid before a colonoscopy.
Foods to Avoid Before a Colonoscopy
1. High-Fiber Foods
Many colonoscopy centers will ask you to cut out high-fiber foods about three days before the procedure. "That means focusing on low-fiber and low-roughage foods to prepare your gut, to start cleaning it out so [your colon lining is] easier to see," says Msora-Kasago.
"Roughage is another term for insoluble fiber, which is the parts of food that cannot be digested," says Naila Arebi, consultant gastroenterologist at Princess Grace Hospital, part of HCA Healthcare UK.
"It is needed in our bodies to help food and waste pass through the intestines. However, residual roughage can remain in your colon, and conceal potential issues that your doctor is looking for."
A low-fiber diet may seem counterintuitive. After all, high-fiber foods — especially plant-based ones — are supposed to help prevent colon cancer, according to the American Institute for Cancer Research. (Fiber basically scrubs out the colon, clearing it of potentially unhealthy buildup, per the University of California San Francisco).
The problem is, high-fiber foods fill up your colon and take several days to clear. That's exactly what you don't want before a colonoscopy procedure.
Fibrous foods to stay away from before a colonoscopy include legumes such as chickpeas, beans and lentils, whole grains, fresh fruits and raw vegetables (cooked is OK), says Msora-Kasago. Raisins, popcorn, corn and potato chips are also on the list.
But these are the guidelines... for now. An October 2018 article in Gastrointestinal Endoscopy reported that restricting dietary fiber the day before a colonoscopy may not actually be all that helpful. "There's a debate about whether restricting diet is necessary," says Msora-Kasago. "The evidence is still evolving."
According to an April 2019 study in Diseases of the Colon & Rectum, folks who followed a low-fiber diet the day before their colonoscopy saw better prep results than those who only had clear liquids. For now, though, the main thing to remember is to closely follow whatever instructions your own doctor gives you.
2. Seeds and Seedy Bread
You should also be aware that some foods will need to be eliminated for up to a week before the procedure.
"All seeds, such as chia, linseeds, sesame, poppy, sunflower, flax, hemp, nigella and pumpkin seeds commonly found in multigrain bread should be avoided for at least one week prior to a colonoscopy," says Arebi.
"Not only do they linger in the colon but may also obstruct the suction channel of the colonoscope and prolong the procedure as the endoscopy team spends time clearing the instrument."
3. Foods Containing Dye
Although no official guidelines specifically recommend avoiding foods with dyes, most colonoscopy centers will tell you to stay away from them before the procedure. The concern is that red dye can stain the colon and make it difficult to see abnormalities, says John H. Ashcraft, DO, chief of colon and rectal surgery at the University of Kansas Health System in Kansas City.
Dye in the colon can also provide potentially misleading information. "Colors such as blue, purple and red can appear as abnormalities, prompting concern," says Arebi.
So don't be surprised if you're asked to forego fluids, Jell-O, ice pops and any other foods or drinks that are red, purple or orange.
If you're not sure what foods contain dye, Kander advises checking the nutritional label for the following:
- Sunset yellow FCF (E110)
- Quinoline yellow (E104)
- Carmoisine (E122)
- Allura red (E129)
- Tartrazine (E102)
- Ponceau 4R (E124)
These are all dyes and should be avoided ahead of your procedure.
4. Solid Foods
Even more painful than restricting fiber and avoiding food containing certain dyes is stopping all solid foods during colonoscopy prep. Even something as seemingly innocent as mashed potatoes must be avoided.
"This is to ensure that there is no residual food in your digestive tract at the time of the colonoscopy and that all the lining of the colon is not obscured," says Arebi.
If you're having difficulty discerning what counts as solid food, Kander says it includes everything that isn't liquid at room temperature. That means "softer" solid foods like cheese, mashed potato and yogurt are all out of bounds.
What to Eat Before a Colonoscopy
So what does that leave? In short: clear fluids, gelatin and ice pops. Specific items that can be enjoyed include bouillon, tea, clear fruit juice without pulp (apple, white grape, white cranberry, lemonade), clear sports drinks and yellow or green Jell-O and ice pops.
Black coffee is fine as well, even if it contains sugar — but not coffee with creamer or milk.
An exception to the clear-liquids rule? Alcohol. "Even though alcohol is clear, it tends to be dehydrating," says Msora-Kasago. It's also not a good idea to have alcohol in your system before a colonoscopy when you're going to be sedated.
Should You Fast Before a Colonoscopy?
As certain foods are out of bounds ahead of a colonoscopy, you might be tempted to fast 24 hours beforehand. Arebi says this isn't necessary.
"24 hours before a colonoscopy, liquids can be consumed including broths and most drinks, provided that they don't contain red, blue or purple food dye," she says.
Two hours before the procedure, it's important not to drink anything at all as this can impair the exam.
Other Colonoscopy Preparation Tips
There are a few other ways to ensure your procedure runs smoothly. If you have opted to have a sedative for the procedure, you should arrange for someone to collect you after your colonoscopy and stay with you overnight.
"This is because some people can have a reaction to the sedative used," says Arebi.
Fatty, fried foods, such as chips, should also be avoided for 2 to 3 days before the colonoscopy as these can digest slowly, along with tough meats.
People with diabetes on insulin may have a separate protocol to follow.
- Harvard Health Publishing: “Preparing for a Colonoscopy”
- American Institute for Cancer Research: “Get the Facts on Fiber”
- Kaiser Permanente: “Low-Fiber Diet for Colonoscopy Preparation”
- University of Wisconsin Health: “Getting Ready for Your Colonoscopy”
- Gastrointestinal Endoscopy: “The Association Among Diet, Dietary Fiber, and Bowel Preparation at Colonoscopy”
- Diseases of the Colon & Rectum: “Randomized Clinical Trial: A Normocaloric Low-Fiber Diet the Day Before Colonoscopy Is the Most Effective Approach to Bowel Preparation in Colorectal Cancer Screening Colonoscopy”
- University of California San Francisco: "Why Fiber Is So Good for You"
- Ruth Kander
- Naila Arebi
- Cordialis Msora-Kasago
- John H. Ashcraft
Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.