Colonoscopy Diet Prep for Diabetics

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Before having a colonoscopy, a diet prep 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 diet prep is not done correctly, some lesions or polyps could be missed during the colonoscopy. A diet prep is always done in combination with another type of bowel prep, such as a cleansing solution; it is not performed as the sole method of clearing the bowel before colonoscopy.


A colonoscopy diet prep 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 hypoglycemia. If you have diabetes and you are taking a bowel prep before a colonoscopy, you may need to monitor your blood sugar levels more frequently and watch for the signs of hypoglycemia.


Check with your doctor about how many carbohydrates you should be taking in each day during your diet prep if you have diabetes. It may be necessary to have some sweetened drinks or glucose tablets on hand in case you develop symptoms of hypoglycemia, such as shaking, sweating, lightheadedness or extreme hunger. The Wolfson Unit for Endoscopy recommends adding 10 g of carbohydrates to bring your blood sugar back to normal levels if you experience symptoms of hypoglycemia. 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 heavy liquids. Liquids on a colonoscopy diet prep to take include apple juice, water, sports drinks, gelatin, frozen pops, diet soda, coffee and broth. 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, 4 oz. of apple juice contains 15 g of carbohydrates while 4 oz. 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.