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People choose to fast for various reasons. Some do it as part of their religious or spiritual practice, while others fast as a weight-management strategy. Short-term fasting might even help lower your blood sugar if you do it safely and under medical guidance.
Fasting might have some benefits for people living with diabetes, but it isn’t recommended for everyone. In this article, you’ll discover how to stabilize your blood sugar levels without eating during a fasting period.
Fasting means not eating, drinking, or both for a period of time — usually during hours when you would normally have a meal. Your doctor might also ask that you fast before a medical test or procedure, or you might decide to fast by choice.
Intermittent fasting is a type of fasting that people often use for health-related purposes, like managing their weight. When you practice intermittent fasting, you eat only during certain hours and skip food during the rest of the day.
Short-term studies suggest intermittent fasting can be safe for people with insulin-treated type 2 diabetes when monitored.
Adjustments to insulin dosing for people with insulin-dependent type 2 diabetes vary by treatment regimen. People with high blood sugar readings while fasting may still need correction dosing. Ask a healthcare professional for personalized guidance on adjusting your insulin regimen while fasting.
There is published research on fasting in people with type 1 diabetes (for example, during Ramadan). But the risk of hypoglycemia (low blood sugar) is higher, and any fasting should be closely supervised. Most health experts don’t recommend it due to the risk of hypoglycemia during the fasting period. If you fast and you have been diagnosed with type 1 diabetes, make sure to inject your long-acting insulin every day.
You should always talk to your doctor before trying intermittent fasting.
During a fasting period, your body uses glucose (blood sugar) and fat as its main sources of energy. In the first phase of fasting, your body uses glucose. This causes your blood sugar to drop.
In response to the drop in blood sugar, your pancreas produces the hormone glucagon. Glucagon, like insulin, helps regulate blood sugar. But instead of lowering your blood sugar level, it increases it to make up for the drop. Glucagon also helps break down fats to create ketones, which then become your main energy source when you’re fasting.
Some people with diabetes might experience hyperglycemia, or high blood sugar, as a result of intermittent fasting.
People with diabetes who don’t take enough insulin may have a blood sugar spike during longer periods of fasting. This spike happens when glucagon tells the liver to release glycogen, which is stored sugar, into the blood.
Some people notice that their blood sugar is higher in the morning after an overnight fast than it is after they eat breakfast. This can feel confusing, but it’s a common pattern called the dawn phenomenon.
While you sleep or go many hours without eating, your body still needs energy. Hormones such as glucagon, cortisol, and growth hormone signal the liver to release stored glucose into the bloodstream, raising blood sugar.
In people with diabetes, high fasting blood sugar levels can be more noticeable. That’s because the body may not make enough insulin or may not use insulin well enough to balance the extra glucose.
Sometimes eating breakfast actually lowers blood sugar afterward because insulin released during the meal helps move glucose from the blood into cells. If your fasting blood sugar is often high, talk with your doctor about what it may mean.
Despite the possible benefits of fasting, like improved fat metabolism, fasting may cause hypoglycemia in some people with diabetes. This is especially a risk if your medications aren’t adjusted properly before a fasting period.
The effects of intermittent fasting in diabetes depend on several factors. Not everyone with diabetes will have the same experience with intermittent fasting. What you experience depends on:
Work with your doctor to make sure you fast safely and that you can keep your blood sugar stable. Your healthcare provider can help you develop a fasting management plan that you can follow during intermittent fasting or while fasting for religious purposes like Ramadan, Yom Kippur, Navratri, or Ekadashi.
Your doctor may tell you to check your blood sugar regularly with a glucose meter while you’re fasting. You’ll probably need to check your blood sugar more often than you typically do. Many people with type 2 diabetes use a continuous glucose monitor (CGM). CGMs can help detect fasting blood sugar trends and guide safe medication adjustments.
Your doctor will tell you when to measure your blood sugar levels so you can monitor changes that happen with eating periods, exercise, and taking medications. Your doctor might also ask you to track when you feel hungry during a fasting period.
While creating your fasting management plan, your doctor will tell you how many calories to eat on fasting days (if your plan allows calories) and on nonfasting days.
Time-restricted eating may be easier and lower risk for some people with type 2 diabetes because it still allows you to eat every day. In time-restricted eating protocols, fasting periods are often short enough not to lead to hypoglycemia. In a typical time-restricted eating fasting plan, you can eat during a six-to-eight-hour window every day. The safest plan for you depends on your medications, risk of hypoglycemia, kidney function, and other health factors.
Make sure your meals include a mix of carbohydrates, protein, and healthy fats. This balance helps you stay energized and maintain healthy blood sugar levels before and after fasting.
Before you begin fasting with diabetes, your doctor might advise you to eat foods with a lower glycemic index. Your body absorbs these foods at a slower rate, so you’ll feel full for longer. They also help keep your blood sugar steady.
Low-glycemic-index foods like fruits, vegetables, beans, whole grains, and low-fat dairy are all great options for before a fasting period. Ask your doctor what portion sizes of carbohydrates are right for you.
Following a fasting period, avoid eating too much sugar or fatty foods. Continue eating balanced foods with appropriate portion sizes, but consider cutting down on fats by using less oil when you cook or opting for grilling or baking instead of frying your food.
Depending on your fasting plan, you may or may not be allowed to drink fluids (for example, water is prohibited during daytime Ramadan and on Yom Kippur).
While you should stay well hydrated throughout your fasting period by drinking water and other sugar-free beverages, try to avoid drinks with caffeine. Fasting can increase the risk of dehydration for people with diabetes.
Your doctor might adjust your diabetes medications or medication dosages while you fast to lower your risk for hypoglycemia or hyperglycemia. For example, SGLT2 inhibitors can raise the risk for euglycemic ketoacidosis, particularly while fasting. Your physician may recommend extra precautions during periods of fasting.
Follow your doctor’s instructions for any adjustments to diabetes management so you can keep your blood sugar stable during a fasting period.
Reading your blood sugar regularly while you fast can help you see if it’s too high or too low. If you see unsafe glucose readings, stop fasting and eat normally for the rest of the day.
You should also stop fasting if you feel unwell during your fasting period. For example, hypoglycemia can cause you to feel shaky or sweaty. If you have low blood sugar levels, take glucose tablets, drink a sugary beverage, or eat a snack to stabilize your blood sugar as you normally would.
High blood sugar levels can cause you to feel extremely thirsty, urinate often, have headaches, and feel tired or fatigued.
If you’re vomiting, have severe abdominal pain, rapid breathing, or feel extremely unwell, seek medical advice urgently and check your ketones if instructed to by your doctor. These symptoms are especially important to look out for while fasting if you use insulin or an SGLT2 inhibitor. These symptoms could be a sign of ketoacidosis.
If you have diabetes, always ask your doctor before fasting, especially if you take insulin or other medications to lower your blood sugar. Be sure to discuss any other health conditions you have that could be affected by fasting, including kidney disease.
Your doctor can explain the health risks and help you decide if fasting is safe for you. Fasting may help some people with diabetes manage blood sugar and lose weight, but it isn’t safe for everyone.
On DiabetesTeam, people share their experiences with diabetes, get advice, and find support from others who understand.
What strategies have you used to maintain your blood sugar while fasting? Let others know in the comments below.
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