Fasting and Diabetes: Benefits and Risks

If you have diabetes and are thinking about fasting for weight loss, blood sugar control, or any other reason, there are both benefits and risks to consider. Fasting may improve insulin sensitivity, reduce inflammation, and support weight loss efforts, but if you have diabetes, it may also increase your risk of hypoglycemia, especially if you take insulin. Surprisingly, skipping meals can lead to high blood sugar as well.

While some people with diabetes swear by a lifestyle that regularly incorporates fasting, there are reasons to be cautious.

“I have many people with diabetes who are able to fast successfully for personal or religious reasons, but we have to approach it safely,” says Nuha El Sayed, MD, interim chief scientific and medical officer at the American Diabetes Association (ADA).

• 16:8 This schedule provides a daily 8-hour eating window, requiring 16 hours of fasting (including the hours in which you’re asleep). Many people choose an eating window of 10 a.m. to 6 p.m., though you can choose any 8-hour window that best suits your needs. People new to this fasting method or who need a little more flexibility can opt for a 14:10 schedule instead.
• Alternate-Day Fasting (ADF) This approach calls for rotating your fasting days (eating zero or very few calories) with normal eating days. Many proponents choose to eat a very small amount of food on their fasting days, approximately 500 calories.
• 5:2 This approach calls for eating normally five days a week while restricting your calorie intake to about 500 calories the other two days of the week. You can choose which days to eat normally and which days to fast, so long as you have at least one non-fasting day in between your two fasting days.
• One-Meal-A-Day (OMAD) As the name suggests, the OMAD approach requires you to consume all of your nutrition for the day in a single meal while fasting for the remainder of the day.

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Of course, not all fasting happens for health reasons: A number of religious or cultural holidays also call for various durations of fasting, including Ramadan, Yom Kippur, and Lent.

Structured fasting schedules may offer a variety of benefits to people with diabetes, including improved “insulin sensitivity, weight loss, and A1C,” says Krista Varady, PhD, professor of nutrition at the University of Illinois, Chicago.

Lastly, if you take insulin, every meal may potentially involve the work of counting carbohydrates and estimating insulin doses. Fasting inevitably reduces the overall workload of dosing for meals. It can also simplify food prep and meal planning, easing the constant burden of “What should I eat today?” by reducing your number of daily meals.

“Knowing how to fast with type 1 diabetes can definitely make things easier,” says Dr. Lake, who has had type 1 diabetes for over 30 years. In situations where it’s difficult to find food that will work with his diet, such as while traveling, he will sometimes skip meals rather than eat food that might make his blood sugar more difficult to keep in control.

Fasting is not without its risks, especially for people with diabetes who take medications that can lower blood sugar levels.

“The medications that need to be carefully monitored and adjusted during fasting are insulin and sulfonylureas,” says Dr. Varady. Your doctor can help you fine-tune your insulin doses, the timing of your insulin, and any other considerations related to fasting.

Other medications may need a bit of adjusting, too, especially if they’re prescribed to be taken with food.

“Anyone with diabetes who wishes to follow a fasting diet should work closely with their endocrinologist,” says Varady. “Your endocrinologist will need to modify your medication use right from the start of the diet. If your medications aren’t monitored and adjusted by your doctor, your risk of hyperglycemia or hypoglycemia is very high.”

All of the fasting approaches discussed above advise you to eat at least a little bit every day. But some people prefer a more aggressive approach, skipping food entirely for 24 hours or more. These prolonged fasts should never be attempted without a doctor’s approval, as they call for more significant medication adjustments, closer attention to your glucose levels, and enhanced medical supervision.

Lake is one proponent of prolonged fasting. He created and participated in an extreme fasting study in an effort to prove that people with diabetes can fast safely without the risk of DKA.

“We just drank water and salt for five days,” says Lake. “Two of us had type 1 diabetes, and the others weren’t diabetic.”

Lake’s experience, however, may be unusual.

“Personally, I wouldn’t advise anyone with diabetes to follow a prolonged fasting diet,” says Varady, who acknowledges that prolonged fasting may have some benefits for people without diabetes. “I haven’t seen any convincing evidence from long-term clinical trials showing that prolonged water fasting is safe in people with type 1 or type 2 diabetes.”

• Fasting may provide several benefits to people with diabetes, including improved insulin sensitivity, reduced inflammation, and weight loss support.
• Going without food, however, may also come with increased risks of hypoglycemia, hyperglycemia, and diabetic ketoacidosis (DKA).
• People with diabetes who want to fast need to consult their healthcare provider before doing so to determine any necessary medication adjustments, particularly with insulin and sulfonylureas, to prevent dangerously low blood sugar levels.