Fasting with Diabetes

Fasting poses some unique challenges for people with diabetes. Here’s how to properly fast without taking any health risks.

By Susan B. Sloane, BS, RPh, CDE

Fasting can occur for medical reasons such as preparing for a test, and for religious reasons as well. To ensure that fasting is done safely, you should always enlist the assistance of your healthcare team in case medication changes are warranted.

Fasting is generally never recommended for patients with type 1 diabetes unless it’s medically supervised, as insulin dosing requirements will change. You will always need some insulin even if fasting, so it is imperative that your entire healthcare team is involved.

Fasting for patients with type 2 diabetes can be done, but your health care team should also be aware of the fast and will give you instructions on how to proceed if changes in therapy are warranted.

The main thing to keep in mind when fasting is that blood sugars need to be tested frequently to avoid unexpectedly low blood sugars (hypoglycemia generally occurs below 70mg/dL (3.9 mmol/L)) or high blood sugars (hyperglycemia is generally considered blood sugars above 200mg/dL (11.1 mmol/L)).

Interestingly enough, fasting in a person with diabetes can cause blood sugar levels to rise unexpectedly because fasting causes the release of extra cortisol which can act as a steroid and cause blood sugars to be elevated.

You also need water to stay hydrated while fasting since fasting without fluids can be dangerous for people with diabetes as they are more prone to dehydration. Some people with diabetes also have other health issues such as heart problems, blood vessel disease, and kidney disease. For this  population, the risk of fasting may be even higher and will require a health care professional’s involvement and advice.

As you can see, fasting can be risky in the person with diabetes, but for some people it can be done safely when you interact with your medical team and receive proper protocols. You will need to review what to do in the event of very high or low blood sugars.

You will also need to review treatment for low blood sugar, and have snacks and other treatments such as glucose tablets on hand in case blood sugars get too low. You may even need to understand (or have your caregiver understand) how to use glucagon which is an injectable “rescue medication” for severe hypoglycemia.

Remember to wear medical ID so that if you have a problem, people and medical personnel will understand that you are living with diabetes and will know how to treat you properly. You should also monitor your urine for ketones, which can be dangerous during fasting and are a byproduct of fat burning for fuel.

After a fast, it is important to eat slowly and not consume large amounts of food quickly both for your digestive system and to make sure blood sugars stay as stable as possible. Again, the most important factor when fasting is to check blood sugars frequently to stay safe. Make sure to get protocols from your own health care team before embarking on a fast, and review these tips before you begin.

Stay well!