Diagnostics > Colonoscopy

Colonoscopy prep: The complete guide

Dr. med. Andre Sommer

Dr. med. Andre Sommer

A colonoscopy is used to diagnose intestinal complaints, unclear anemia and for cancer screening. In a colonoscopy, a so-called endoscope is inserted into the intestine, which is then assessed by the doctor.

That sounds uncomfortable at first. In fact, the examination is almost always done under anesthesia and is not painful. Many people tend to feel that preparation with a colon cleansing is uncomfortable. That is because: Only a clean intestine ensures a good view and thus a reliable diagnosis. Otherwise cancer precursors can be overlooked or the examination - and thus the preparation - must be repeated completely. Careful colon cleansing can also reduce the risk of (very rare) complications.

Preparation essentially means:

  • Abstaining from certain foods for a few days
  • Fasting for 12 to 24 hours just before the exam
  • Drinking several liters of a laxative solution

Note: If the colonoscopy is performed due to digestive problems and is without results (that is, everything is "OK" for the time being), those affected and the doctors are often at a loss. The diagnosis of irritable bowel syndrome is then often made then. In this case, individual nutritional therapy is a very good therapy option and is reimbursed by most health insurers. We also work with specially trained specialists and offer a range of therapies, which you can find out more about here.


What foods should you not eat in advance?

Patients who want to have a colonoscopy will get written instructions from their doctor beforehand. However, as studies have shown, the instructions are often not followed correctly or not properly understood. It is therefore advisable to take the time to read them.

However, there are few studies regarding an optimal meal plan before a colonoscopy. Previous results show that a low-fiber and easily digestible diet the day before the examination is better for colon cleansing. The amount of food does not have to be reduced. Many doctors recommend such a diet not only for the day before the exam, but for four to five days before the examination.

You should definitely avoid high-fiber foods such as whole grains. It is also not advisable to consume fiber-rich fruits and vegetables as well as fillers and swelling agents (e.g. flax seeds or psyllium).

Food with granules, seeds, skin and peels are often also high-fiber foods. Above all, these can clog the fine instruments during a colonoscopy. You should avoid kiwis, grapes, tomatoes, legumes, nuts and poppy seeds, among other things. Cabbage should also not be on the menu before a colonoscopy due to its flatulent properties.

In addition, iron-containing preparations should not be taken several days in advance. They discolor the intestinal wall and can harden the stool.

High-fiber food Low-fiber food
Whole grain bread, dark bread White bread, toast, rusks
Müsli Rice, potatoes (without skin), durum wheat noodles
Many types of fruit (raw; e.g. citrus) Lean meat, fish
Many types of vegetables (e.g. asparagus, leafy greens) Eggs
Meat and vegetable broth without additions
Some vegetables (for example carrots, peeled zucchini)

When should I stop eating and drinking?

Things get really serious the day before the upcoming examination. A laxative drinking solution must be consumed with several liters of water. At this point, there are clear guidelines as to when you should stop eating food. And only clear liquids are allowed as drinks.

Avoid Instead The day before On the day of the exam
  • Milk, mixed drinks containing milk
  • Cream
  • Fruit juices with pulp
  • Water
  • Tea / coffee (without milk)
  • Clear juices
  • Lemonade
  • You can drink as much as you like, but at least several liters
  • Depending on the preparation; last drink usually about 4 hours before the examination
  • Fruits with small and large seeds
  • High-fiber diet
  • Fruit and vegetables rich in fiber
  • Legumes
  • Iron supplements
  • Filling and swelling agents
  • Low fiber and easily digestible food
  • Breakfast (Depending on the preparation and the time of the examination, drinking of the laxative solution is started at different times; after that you should no longer eat solid food.)
  • Depending on the preparation; As a rule, you should no longer eat from midday, clear broth is usually still allowed afterwards
  • No breakfast
  • Second dose of the drinking solution

What about coffee, alcohol and chocolate?

Generally, coffee is no problem. However, some doctors recommend not drinking coffee, black tea, or dark juices from the night before as they could discolor the intestinal wall. Chocolate also has such an effect. The darker the chocolate, the more fiber it contains. The general rule: The instructions can differ slightly from doctor to doctor, since some specifications are a "matter of taste" for the doctor.

Alcohol should not be consumed on the day of the exam. A glass of wine the night before is usually not a problem. However, it should be borne in mind that alcohol dries out the body further and the effects on a fasted body are more difficult to control.

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Is preparation possible without laxatives?

The principle behind the action of laxatives is very simple: Laxatives contain several salts that draw water into the intestine. The water in turn effectively flushes out food residue.

So far there are no accepted alternatives to drinking a laxative solution.

Different types of intestinal enemas have been tested primarily in studies as a single or combined measure. However, these procedures are mostly reserved for patients who, due to illnesses such as dementia, cannot perform an adequate colon cleanse themselves. This variant can hardly be described as more pleasant.

Fasting lasting several days during colon cleansing should be combined with laxatives and discussed with the doctor in advance.

Preparation for a colonoscopy in special situations

A colonoscopy is usually essential to diagnose an inflammatory bowel disease. In most cases, the preparation is the same as for a preventive colonoscopy. With an active, heavy inflammation, however, oral laxatives are not always recommended, as this can lead to an expansion of the intestinal wall. The attacked intestinal wall then tears more easily than in healthy patients. In such cases, a doctor decides whether the procedure must be postponed or can be done without colon cleansing.

Diabetics need to monitor their blood sugar closely. With insulin dependence, insulin should not be injected if nothing is being eaten to avoid hypoglycemia. Blood thinning medications are usually discontinued for a certain time beforehand in consultation with the doctor. However, other drugs should usually be taken normally.

General caution applies to patients with heart, kidney, and liver problems. Here, the drinking habits can be adjusted so that the body does not retain too much water. For children and people who have swallowing problems, or for those who have problems drinking after a stroke, drinking large amounts can be problematic.

Patients with many diseases, known large polyps, and previous complicated colonoscopies have complications more often than others. For this reason, an in-patient colonoscopy in the hospital is safer.

Dr. med. Andre Sommer

Dr. med. Andre Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara Care.

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