When is Fasting Necessary?


Fasting is a common practice for different spiritual and religious observances. It is also done for different medical purposes, including blood tests, surgery and other procedures. Below is a look at some of the most common reasons why patients may be asked to fast.

In order for accuracy, when getting certain blood tests done (i.e. to check your glucose, cholesterol, vitamin B12 and iron levels), patients are typically asked to fast anywhere from 8 to 12 hours before the test is performed. This means avoiding all food and beverages, including alcohol. It’s also recommended that you avoid chewing gum, smoking and exercise, as these can increase your digestion. If you eat, drink or do any of these activities before your blood test, it could affect the outcome of your results and you would be required to repeat the test. If you are on certain medications, it is generally safe to take them with a small amount of water, though you should always check with your physician or the laboratory if you are unsure.

To avoid starving throughout the day, Dr. Ali Ghahary recommends that patients go for blood work first thing in the morning.

Patients are also required to fast for certain medical procedures. If you are undergoing a gastroscopy, you will be asked to fast for as least 6 to 10 hours before the procedure is performed. This is to give the doctor performing the procedure a clearer view of your stomach and intestines, and to also prevent you from vomiting.

Similarly, you will also be asked to fast for surgeries that require general anesthesia. If there is food or fluid in your stomach at the time of your surgery, you risk the potential of inhaling vomit into your lungs, which can lead to complications such as pneumonia. Post-operative, many patients complain of feeling nauseous due to the anesthesia, so it is important to keep your meals light during the first day or two of recovery. Eating saltine crackers or sipping on water or ginger ale are the best options.

If you are undergoing a colonoscopy, you are allowed to eat a diet that is low in fibre for up to 2 or 3 days prior to the procedure, and have only clear liquids the day before – for example, water, apple juice, black coffee or jello. The night before the colonoscopy, you will be asked to drink a beverage that will help to empty your bowels, and you will be required to fast the day of the procedure for approximately 2 or 3 hours depending on your doctor’s recommendations.

If you are undergoing any of these tests or procedures and require fasting but are unsure as to what, exactly, you need to do, never hesitate to reach out to your family physician with any questions you might have.

If you are unable to make an appointment see your family physician, Dr. Ali Ghahary is available to see patients at Brentwood Medical Clinic on a walk-in basis.