How to Prep for a Colonoscopy: Diet Tips, When to Start, and More

If you’re due for colorectal cancer screening, you might be getting ready to have a colonoscopy. While the procedure itself is usually quick and pain-free, the colonoscopy prep required beforehand can seem intimidating.

If you’re not familiar with this test, a colonoscopy is one of the recommended tests to screen for colon or rectal (colorectal) cancer in people who are not having symptoms. A colonoscopy test looks for polyps and signs of cancer or other problems in the colon and rectum. A colonoscopy can even prevent colorectal cancer by finding polyps so they can be removed before they turn into cancer.

It’s normal to have questions and even fears ahead of a colonoscopy, especially if it’s your first one. You might be wondering, “What can I eat before a colonoscopy? Do I have to follow a certain colonoscopy prep diet? And when can I expect to start spending a lot of time in the bathroom?”

In fact, studies have shown that the fear of colonoscopy prep can keep people from getting their recommended screenings. But keeping up with your colorectal cancer screening is crucial for finding problems as early as possible.

While the prep for a colonoscopy may not be pleasant, it’s important to empty out your colon as much as possible before the test. The prep instructions can vary based on your health status, your doctor’s preferences, and where you get screened. Your doctor or nurse at the screening location will give you detailed instructions on what to do before your colonoscopy.

What to do 1-2 weeks before your colonoscopy

Typically, you won’t need to make any changes to your diet 1-2 weeks before your colonoscopy. However, you might need to stop taking certain medications about a week before the procedure. For example, your doctor might recommend that you stop taking medications that increase your risk of bleeding, such as aspirin, ibuprofen, and other blood thinners.

“How long you should stop a blood thinner before a colonoscopy varies based on the drug and the reason you are on the blood thinner. But usually, it is between 3-7 days before the colonoscopy. Make sure you talk with the doctor who prescribes your blood thinner about stopping it for procedures like colonoscopies,” said Suneel Kamath, MD, an American Society of Clinical Oncology (ASCO) expert and gastrointestinal oncologist at the Cleveland Clinic.

You might also have to stop taking certain supplements like iron, fiber, and fish oil a week before your appointment. These supplements could interfere with the success of your colonoscopy. Ask your doctor ahead of time when to stop taking your usual medications or supplements.

Diet changes in the few days before your colonoscopy

You might be instructed to make some diet changes ahead of your colonoscopy test. Around 3 to 5 days before the procedure, it might be helpful to start following a low-fiber-food diet This means avoiding high-fiber or fiber-rich foods like:

• Granola
• Nuts
• Seeds
• Whole-grain bread
• Whole-grain rice
• Fruits and vegetables with skin or seeds

Fiber-rich foods are more difficult to digest. This can make the bowel prep you’ll have to do the day before your colonoscopy more difficult. Instead, opt for low-fiber foods like:

• Milk
• Cheese
• White bread
• White rice
• Applesauce
• Chicken
• Broth

In the days before your colonoscopy, you'll be instructed not to eat foods or drink beverages that are red or purple. These colors can remain in your colon and can look like blood.

Your doctor will provide you with instructions on which specific foods to avoid and for how long.

What to do the day before your colonoscopy

The day before your colonoscopy, your doctor will likely recommend you start following a clear-liquid diet. This means sticking to fluids like water, coffee, and broth.  The day before, you’ll also start taking the medicines in your bowel prep kit or following the instructions provided by your doctor to clear out your bowels.

“Taking the prep correctly is vital for getting a colonoscopy result we can trust,” said Dr. Kamath. “If stool obscures parts of the colon wall, your gastroenterologist might say your colonoscopy was normal or clean. But the reality is, a polyp or tumor might have been hidden because the prep wasn't good. If the prep is poor and a lot of stool is found, then the colonoscopy has to be repeated in the few weeks after the first one, which puts you through the same prep all over again.”

The type of bowel prep you will be given can vary based on your provider. The prep medicines may include laxative pills or powders to mix into clear liquids to clear out your bowels as much as possible. Sometimes the prep is premixed in a laxative formula that you drink at certain times over a day or two.

Once you begin taking the prep, its effects will usually kick in within a few hours. This means you’ll be spending a lot of time in the bathroom. “Remember the point of all of this is to give you diarrhea and make it so your stool output is only liquid and not brown at all,” said Dr. Kamath.

It’s crucial that you follow all of the directions of your prep very closely. Be sure to read the instructions well ahead of time in case you need to buy any of the prep medicines. And make sure that you take all of the prep, even if it feels like you’ve gone to the bathroom enough.

“Lots of people get worn out in the middle of the prep, talk themselves into thinking they've drank enough, and quit early,” said Dr. Kamath. “Most of those people are coming back a second time for another colonoscopy and have to do the prep all over again.”

If you find yourself struggling through your bowel prep, remember to stay hydrated. Always keep a water bottle or electrolyte drink with you, even in the bathroom.

Finally, if you are still taking medications the day before your colonoscopy, it might be time to stop some of them. Check your test instructions and talk with your doctor about what’s recommended for you.

Diet on the morning of your colonoscopy

Your doctor will likely recommend you don’t eat or drink anything the day of your colonoscopy. However, you might have to do additional bowel prep the morning of your procedure. Your doctor will tell you what’s required ahead of time.

Tips for the day of your colonoscopy

There are several tips to keep in mind for the day of your colonoscopy. These include:

• Wear loose, comfortable clothing to your appointment.
• Don’t wear jewelry or a watch, as they will have to be removed.
• Ask your doctor what anesthesia or sedative they plan to use. This can help you know how groggy you’ll be for the rest of the day and whether you might need additional help at home.
• Plan to rest for the remainder of the day following your appointment. And check the post-colonoscopy instructions to know what you should and shouldn’t eat that day.

You should also keep in mind that you won’t be able to drive yourself home from your colonoscopy. This is because the sedative given before the procedure won’t be completely worn off by the time you leave. Be sure to arrange for someone to take you to and from your appointment beforehand. “Many centers require the driver to stay while the patient gets the colonoscopy, too,” said Dr. Kamath. “So make sure you know the policies around this and that your driver is available for what is required.”

If you don’t have someone to come with you to your appointment, talk with your health care team. They can point you to transportation resources that might be available to you.

Dr. Kamath noted that colonoscopies are the best way to screen for colorectal cancer because they can help prevent the disease from developing.  And regular colonoscopies can find colorectal cancer early. But if you find having anxiety around colonoscopy prep is keeping you from getting screened, talk with your doctor. They can talk with you about other screening options that might be available to you. “The alternative options can catch cancer at an earlier stage, but they can’t remove pre-cancerous polyps like a colonoscopy can, which ultimately can prevent the cancer entirely,” said Dr. Kamath.

Learn more

Learn more about colorectal cancer screening from the American Cancer Society:

• Cancer screening resources and locator
• Digestive system anatomy
• Colorectal cancer screening tests
• Insurance coverage for colorectal cancer screening

Dr. Kamath is a member of ASCO’s Patient Information Editorial Board.