Colonoscopy Diet Prep for diabetics

Before having a colonoscopy, a preparation is necessary to clear the bowel of any waste, which allows the physician to see all of the internal structures without any obstructions. If the preparation is not done correctly, some lesions or polyps could be missed during the colonoscopy. A preparation is always done in combination with a cleansing solution; it is not performed as the sole method of clearing the bowel before colonoscopy.


A colonoscopy preparation involves following a clear liquid diet for a prescribed time before the procedure. Depending on physician orders, this may be one to two days before the colonoscopy. Changing the diet from solid foods to clear liquids may affect blood glucose levels among diabetics, potentially causing hypoglycaemia. If you have diabetes and you are taking a bowel preparation before a colonoscopy, you may need to monitor your blood sugar levels more frequently and watch for the signs of hypoglycaemia.


Check with your doctor about how many carbohydrates you should be taking in each day during your preparation if you have diabetes. It may be necessary to have some sweetened drinks or glucose tablets on hand in case you develop symptoms of hypoglycaemia, such as shaking, sweating, light-headedness or extreme hunger. It is recommended to add 10 g of carbohydrates to bring your blood sugar back to normal levels if you experience symptoms of hypoglycaemia. Examples of these types of beverages that you can have would include 50 ml of grape juice, 100 ml of cola, 120 ml of unsweetened fruit juice or 140 ml of ginger ale.

Clear Liquids

The clear liquid diet taken before a colonoscopy consists of no solid foods and no milk or dairy products. Liquids recommended during bowel cleansing for colonoscopy include apple juice, water, sports drinks, jelly, frozen pops, diet soda, coffee, tea and broth. Take at least one glass of Rehydrate per hour. You will need to monitor how many carbohydrates you consume while taking the diet prep, according to your doctor’s orders. Some clear liquids contain carbohydrates, while others do not. For example, 100ml of apple juice contains 15 g of carbohydrates, while 100ml of white grape juice contains 20 g.


If you have the option, try to schedule your colonoscopy early in the morning so that you can eat after the procedure. This may help to regulate your schedule of checking your blood sugar levels and taking insulin. Although you will be taking clear liquids only for the prep, your doctor may recommend that you continue taking your insulin or other medications for your diabetes. You may need to regulate how much you take depending on your glucose levels. For example, you may need to decrease your short-acting insulin by one-half of the dose to compensate for decreased food intake. Talk with your doctor about how much of your medications you should be taking while consuming a diet prep.

Diabetes Instructions for Colonoscopy Preparation and Procedure

These are general guidelines. Please call the health care provider who manages your diabetes for questions. For people with diabetes, any procedure that causes you to miss a meal or change your usual meal plan will require special planning to safely manage blood glucose.

INSULIN AND DIABETES PILLS: If you are a diabetic, it is important to monitor your blood sugar while doing the bowel preparation. You should take only ½ of your usual dose of insulin or pills on your prep day. You should not take any diabetic medications on the day of your procedure. Please be sure to check your blood sugar at home at all meals, at bedtime and on the morning of your exam.

Please use these tips to schedule your examination:

Schedule the appointment for early in the day so that you can eat afterwards and take your medication as close to the usual time as possible.
Check your blood glucose level before all meals and at bedtime on the preparation day and on the day of the procedure.
Check your blood glucose if at any time you have symptoms of low blood glucose or very high blood glucose.
Bring your blood glucose meter, test strips, and a low blood glucose treatment with you on the day of the procedure.


Clear liquid food choices for the day before your colonoscopy:

  • Aim for 45 grams of carbohydrate at meals and 15‐30 grams of carbohydrate for snacks
  • Avoid foods that are red or have red dyes (cherry, berry, or grape flavours)

Sample of Clear Liquid Choices with Grams of Carbohydrates:

  • Apple juice (100ml) 15 grams of carbohydrates
  • White grape juice (100ml) 20 grams of carbohydrates
  • Sports drink such as Gatorade (200ml) 14 grams of carbohydrates
  • Gelatin (Jelly), regular sweetened (1/2 cup) 15 grams of carbohydrates
  • Orange popsicles or ice pops (read the label) 15 grams of carbohydrates
  • Italian ice‐‐not sherbet (read the label) 30 grams of carbohydrates
  • Sugar (for coffee or tea) (1 teaspoon or packet) 4 grams of carbohydrates

Food items without carbohydrates:

  • Fat‐free broth, bouillon, or consommé
  • Diet clear soda
  • Coffee
  • Tea (unsweetened or diet)
  • Flavoured water