Colonoscopy Bowel Prep: What to Eat, Drink and Expect

Most people who have had a colonoscopy say the same thing: the procedure is short, and the day of preparation is the hard part. Prep matters because the doctor can only see what is clean. This guide explains how bowel prep usually works, what you can eat, how people make the drink easier to get down, and what to ask if you are prone to constipation. It is general information. The hospital doing your colonoscopy will give you its own instructions, and those are the ones to follow.

What does bowel prep for a colonoscopy involve?

Bowel prep has two parts: a few days of eating less fibre, then a laxative drink that empties the bowel completely so the lining can be seen clearly. Many hospitals use a split schedule, with one dose the evening before and a second dose on the morning of the test, but the product and timing depend on the hospital and on you.

There is no single best prep. Doctors choose between several products, which differ in how much you drink, how they taste and who they suit. Kidney or heart problems, diabetes, pregnancy and some medicines can change which prep is safe for you, so tell the hospital about your health and all your medicines when you book. If you have used a prep before and could not finish it, say so, because there may be an option with less volume.

The aim of all this is a clear view. If the bowel is not clean enough, small polyps can be hidden, and the test may have to be repeated.

What can you eat before a colonoscopy?

In the days before, you usually switch to a low-fibre (low-residue) diet, then move to clear fluids only on the day before the procedure. Low-residue food leaves less behind in the bowel, which helps the laxative do its job.

Foods often allowed on a low-residue diet include white bread, white rice, plain pasta, eggs, plain chicken or fish, and clear soup. Foods usually avoided include wholegrain bread and cereals, nuts, seeds, raw vegetables, fruit skins, beans and lentils. Seeds and skins cause the most trouble, because they cling to the bowel wall.

Clear fluids are drinks you can see through: water, clear broth, apple juice without pulp, clear sports drinks, black tea or coffee without milk, and plain jelly. Many hospitals ask you to avoid red and purple colours, which can look like blood on the camera. How many days of low-fibre eating you need varies between hospitals, and people with slow bowels are sometimes asked to start earlier.

Are there alternatives to drinking the prep liquid, such as pills or MiraLAX and Gatorade?

Alternatives exist, but choosing one is a decision for your doctor, not a swap to make on your own. Depending on the country, options include lower-volume liquid preps, tablet-based preps and, in some US practices, an over-the-counter laxative powder mixed into a large sports drink.

Whether any of these suits you depends on your kidneys, your fluid and salt balance, your other medicines and what the hospital normally uses. Tablet and low-volume preps still require a lot of water alongside them. The MiraLAX and Gatorade approach is used by some doctors and not by others, and those products are not sold everywhere. If the standard drink made you vomit last time, ask in advance for a different option and for anti-sickness medicine, rather than trying to change the plan on the evening itself.

Some hospitals, in China and elsewhere, can give an extra cleansing enema on the morning of the test if the bowel is not clear. Patients in China report that the hospital checks whether the bowel is ready before going ahead. Ask your hospital what it does, rather than relying on it.

How can you make colonoscopy prep easier to drink?

Chilling the drink, sipping through a straw and following each mouthful with a clear chaser are the tips people mention most. Other small things help too.

Not everyone likes it cold. Drinking a large volume of cold liquid while your bowel empties can leave you shivering, so some people prefer it at room temperature and keep a blanket and warm broth nearby. If you feel sick, slow down for a while rather than stopping, and call the hospital if you vomit or cannot keep it down. Finishing the full dose matters more than how fast you drink it.

Can you start colonoscopy prep earlier or change the timing?

Do not change the timing yourself; call the hospital first. The schedule is worked out backwards from your appointment and from the fasting rules for sedation, so moving it can leave the bowel less clean at the time of the test, or leave too little time with an empty stomach before sedation.

The second dose is timed so that the last part of the bowel is clear when the doctor looks. Skipping it, or taking both doses the evening before, often leads to a poorer view. You are also usually asked to stop all drinking a set time before sedation. If the morning dose means waking very early or you have a long journey to the hospital, ask whether the timing can be adjusted or whether a later appointment is possible.

If you are travelling for your colonoscopy, stay close to the hospital for the night before and the morning of the test, because prep makes travel during those hours difficult. In China, public hospitals publish itemised prices: at one public hospital an electronic colonoscopy is listed at CNY 353 (≈ USD 53) and sedation at CNY 260 (≈ USD 39), about CNY 613 (≈ USD 91) before bowel-prep drugs, biopsies and pathology, according to its published price list. Prep drugs are charged separately, so check that they are on any quote you receive.

What if you are prone to constipation?

Tell the hospital when you book, because people with chronic constipation are more likely to have an incomplete clean-out and may be given a longer low-fibre period, an extra laxative in the days before, or a larger prep.

By the end of the prep, what comes out should be clear or pale yellow liquid. If it is still brown or contains solid pieces, call the hospital before you set off. Do not take extra laxatives that were not prescribed. A poor clean-out is not a personal failure, and repeating the test with a stronger plan is common.

If you have not opened your bowels for several days before the prep, or you have pain, swelling or vomiting, contact the hospital or a doctor before you start drinking the prep.