Colonoscopy Prep Diet
At least one day before the procedure, your doctor will ask you to radically alter and limit what you eat. Kaiser Permanente recommends patients start a low-fiber diet three days before and switch to liquids only the day before.
Because policies and timelines for the procedure can vary, get your colonoscopy instructions early and don’t wait until the last minute to read them so you can be fully prepared.
Stopping Solid Foods (in Most Cases)
The ASGE says that you will most likely not be able to eat solid foods the day before your procedure. Your diet may be limited to clear broth, coffee or tea (without cream), gelatin desserts (with no added fruit), and clear fruit juices, such as apple juice but not orange, grapefruit, or prune.
Typically, no milk is allowed because traces can hide a possible polyp in the wall of the colon, according to the advocacy group Fight Colorectal Cancer. Also alcohol is not recommended because it can be dehydrating and interfere with sedatives used in the procedure.
Audrey Calderwood, MD, director of the GI Cancer Risk and Prevention Clinic at the Dartmouth Geisel School of Medicine in Hanover, New Hampshire, and an ASGE member, notes however that a “low-residue” diet may be an option instead of a liquid diet.
The low-residue diet eliminates any high-fiber foods, but allows foods such as white bread, chicken breast, deli turkey, eggs, and well-cooked or pureed vegetables.
“Studies have shown that a low-residue diet is no worse than a liquid diet, but many doctors don’t suggest it because they’re worried that if they give patients an inch, they will take a mile,” says Dr. Calderwood, stressing that patients may veer from the diet, which might then require a repeat colonoscopy.
Still, she encourages patients to ask their doctors about this option because some may find it more tolerable, and if it makes the difference between getting a colonoscopy and not, then it should seriously be considered.
Certain Foods Can Be More Problematic
Specific foods may not move readily out of the colon. Jen Casper, NP, in the GI department at the Mayo Clinic Health System in La Crosse, Wisconsin, advises patients to not eat seeds, nuts, grains, popcorn, and certain heavy fiber foods a week prior to a colonoscopy because these can get stuck. “Polyps can be missed if the colon isn’t squeaky clean,” she says.
Avoid Fluids, Gelatin, or Ice Pops With Red, Blue, or Purple Coloring
Kaiser Permanente says these food colorings can make it difficult to see clearly and make an accurate diagnosis. Yellow and green colorings are considered okay.
The Dreaded Bowel Prep
In most cases, the colonoscopy procedure takes no longer than 30 to 45 minutes, according to the ASGE, and your doctor will keep you as relaxed and comfortable as possible. The doctor passes a long, flexible tube with a camera (a colonoscope) along the entire length of the large intestine (colon) and rectum, and carefully examines the lining. In all but a small number of cases, patients receive a sedative and there is little or no discomfort.
On the other hand, a bowel flush will take many hours and your doctor will not be there to help you. This is the part of the colonoscopy preparation — on top of the restrictive diet — that most people worry about because it usually involves drinking large quantities of special prep liquid and many trips to the bathroom.
One other piece of advice from before you begin the prep: Tell your doctor what drugs you are taking. Most medications can be continued, but some can interfere with either the prep or the colonoscopy. For example, the ASGE warns that certain diabetes drugs including semaglutide and tirzepatide can slow the rate at which your stomach contents empty, and make sedation risky.
The taking of bowel prep fluids or medications typically starts the afternoon or evening before your colonoscopy.
Bowel prep kits contain a slightly different mix of ingredients, but most include an osmotic laxative that makes you want to have a bowel movement, and electrolytes to replace those you lose as you rapidly purge your bowels.
Below is an overview of the options available.
Polymer-Based Formulas
The most commonly prescribed bowel prep formulas for cleaning the intestines use a polymer-based laxative known as polyethylene glycol 3350 (PEG), according to the Cleveland Clinic. PEG is not absorbed by the colon and doesn’t disturb the intestinal mucosa. Standard solutions come in powder form, which you mix with 4 liters (about 1 gallon) of water.
For many, drinking a big jug of solution over a few hours can be very challenging. There are newer alternatives that only require drinking 2 liters of solution — 1 liter in the evening before the procedure and one the morning of the procedure.
Casper explains that patients should drink solution in the morning because the colon makes mucus overnight, doctors don't want any of that in the colon when they do the exam.
“We've also learned ways to make it taste better to make it more palatable” she says. Different flavor options include lemon-lime, cherry, orange, pineapple, and even black currant.
Saline-Based Formulas
Saline-based laxatives provide an alternative to drinking the colon prep because they come in tablet form. The active ingredients include sodium phosphate (NaP) and often other mineral salts such as potassium and magnesium, according to the Cleveland Clinic.
Generally, this type of prep requires taking 24 tablets — 12 the night before and 12 the morning of the procedure, according to Jean Wang, MD, professor of medicine in the division of gastroenterology at Washington University School of Medicine in St. Louis. “Some people prefer the tablets and they are just as good as the liquid prep,” she says. Some saline-based laxatives also come in a low-volume liquid formula.
No matter what approach you choose, you can expect many trips to the bathroom for purging. The goal is to have nothing but clear liquid coming out when your prep solution is finished. The ASGE says you might experience some bloating and cramping, and you should expect to spend a lot of time on the toilet.
Colonoscopy Prep: Planning Ahead
Now that you know what to expect, here are some tips that can help you get through it:
- Shop for the right supplies. Pick up plenty of sports drinks, ice pops, and gelatin, but remember to stay away from red, blue, and purple varieties. Get yourself some chicken or beef broth if you like. You might also want to pick up some medicated pads or wipes to soothe your sore bottom.
- Clear your schedule. Once you start the bowel prep, you will not be straying far from the bathroom. Get some help if you are responsible for kids or aging parents. Stock up your bathroom with some good reading material.
- Drinking the PEG solution gets old quickly. You can add flavor with powdered drink mix or lemon or lime juice, drink it chilled, or just hold your nose and chug it down.
- Wear loose, easy-fitting clothing. Choosing comfortable clothing will help you relax.
Advances That Make Colonoscopy Easier
Knowing what to expect from the procedure itself can ease your mind as you head in for a colonoscopy.
Casper finds that some people have misconceptions — especially older adults. “Years ago, they put a type of tube into the rectum without sedation,” she says. “As you can imagine, it was very uncomfortable. So a lot of older people say I'm never doing that again.”
Today, it’s common to be deeply sedated during the procedure so you sleep through it and don’t feel a thing. Arielle Kanters, MD, a colorectal surgeon with the Cleveland Clinic, uses “conscious sedation” that puts patients in a twilight state using partial anesthesia. “This way I can explain to them what I’m doing and they can tell me if they are uncomfortable,” she says.
Dr. Kanters adds that while the basics of the procedure have not changed much in the past several years, newer tools have made it easier to take out more difficult-to-remove polyps.
Ultimately, the more you know about getting a colonoscopy the easier it should be.
“We find a lot of patients are very nervous and scared coming in for their first time and they all say afterwards, oh, it was much better than they thought it was going to be,” says Dr. Wang.
She stresses that people often find reasons to put off the procedure — and that’s a mistake.
“A lot of people think if they don't have anyone in their family who's had colon cancer, then they're not at risk,” she says. “That’s a misconception because most people who get colon cancer do not have a family history of it. Also, a lot of people will have a delayed diagnosis of colon cancer because they may dismiss symptoms like rectal bleeding or blood in the stool, thinking it’s just hemorrhoids.”
Colonoscopy is still the only test that allows your doctor to inspect your colon and remove any polyps at the same time. Now that you know what to expect and how to prepare, don't let fear of colonoscopy stop you.
Additional reporting by Chris Iliades, MD.
