Fasting and Diabetes
There's a lot of buzz about fasting — that is, not eating for a certain period or cutting back drastically — for better health. You may want to fast to eat fewer calories and lose weight. Or maybe fasting is part of your religious practice. But if you have diabetes, is it safe and will it help you lose weight, control your blood sugar, and maybe even need less medicine?
Perhaps. Some studies suggest fasting may be helpful for people with diabetes. But it's not a mainstream treatment. The American Diabetes Association recommends making lifestyle changes, including medical nutrition therapy and more physical activity, as the cornerstones for weight loss and good diabetes control.
If you're thinking of trying a fast and you have diabetes, you'll want to know what the risks are, how to avoid them, and why you should check with your doctor first to make sure fasting is safe for you.
Intermittent Fasting and Diabetes
Intermittent fasting is a popular eating plan that many claim improves overall health. You may have heard this trend helps people lose weight, improves blood sugar control, and reduces blood pressure, cholesterol, and inflammation.
But what exactly is intermittent fasting? This diet plan involves eating only during specific periods of the day or week and fasting — or not eating anything — the rest of the time. The idea is to reset your eating patterns and get used to being satisfied with fewer calories by not constantly snacking. Some fasts don't allow any food at all. But on intermittent plans, you follow a pattern of fasting and then eat normally.
Three types of intermittent fasting plans include alternate day fasting, 5:2 fasting, and time-restricted eating.
Alternate day fasting
For this plan, you follow your regular diet one day and then eat around 500 calories (or 25% of your normal calorie intake) the next day, repeating this pattern throughout the week. This eating pattern may be challenging if you have diabetes because your blood sugar is directly affected by how much food you eat. In this case, on fasting days, you'll struggle to maintain a normal blood sugar if your body doesn't produce enough insulin (common in type 1 diabetes) or if your body doesn't use insulin properly (common in type 2 diabetes). If you have diabetes, doctors don't recommend alternate day fasting on your own. Rather, work closely with your doctor to make sure you are fasting safely — or to make sure you can fast at all.
5:2 fasting
The popular 5:2 plan has you eat a regular healthy diet five days a week and cut down to about 500-800 calories on the other two days. Similar to alternate day fasting, if you have type 1 or 2 diabetes, you can do 5:2 fasting under the close supervision of your doctor. Your doctor may adjust your medication schedule and dosages and give you instructions on how frequently to check your blood sugar.
Time-restricted eating
This plan is when you get all your calories for the day during a specific number of hours. For instance, on an eight-hour plan, you might eat from 10 a.m. to 6 p.m. and then not again until the next day at 10 a.m. This fasting plan is a good option if you have diabetes because the consistent eating schedule makes it easier for your doctor to adjust your medication, if needed.
Some people fast for several days or even weeks at a time — for example, for religious reasons. But not eating for more than 24 hours when you have diabetes can be dangerous. If fasting for religious reasons is important to you, talk with your doctor about how to fast safely. Your doctor will support you with recommendations from science-backed guidelines.
Is Fasting Good for Diabetes?
More research is needed to know if fasting is safe long term, whether you have diabetes or not. Most studies on the effects of intermittent fasting have been done on overweight, middle-aged adults. More research is needed to determine if it is safe for people who are older or younger or people already at a healthy weight.
Fasting may have some general health benefits. For example, it could cut down on inflammation, help with weight loss, and lower cholesterol. Fasting may also improve the way your body manages glucose (blood sugar). The American Diabetes Association notes that if you're overweight or have obesity, weight loss can help lower your A1c level (a gauge of your blood sugar control over the last two to three months) and lower your risk of heart disease. But fasting isn't required for weight loss.
Fasting may also affect how much insulin medication you need. In one study, people with type 1 diabetes who stuck with a fasting plan were able to lower their insulin dose.
Some organs that play a role in diabetes may benefit from fasting, too. Your body stores extra glucose in a form called glycogen in your liver. It takes your body about 12 hours to use that glycogen. If you don't eat, your body begins to burn fat instead of glycogen for energy. That helps with weight loss. It also gives your liver and pancreas (which makes insulin, the hormone that controls blood sugar) a break.
Can Intermittent Fasting Help Reverse Diabetes?
There is not enough evidence to prove that intermittent fasting reverses diabetes. While more research is needed, several recent scientific studies suggest that intermittent fasting is safe and beneficial for people with diabetes. A 2023 study shows that time-restricted eating helps people with type 2 diabetes lose weight and improves long-term blood sugar control.
Another 2023 study suggests that intermittent fasting may lead to type 2 diabetes remission. But findings of this study are limited by a small sample size (number of people studied) and a very specific type of fasting (Chinese Medicine Nutrition Therapy) that is not mainstream in the U.S.
If you have diabetes and are interested in the possible benefits of intermittent fasting, here's the bottom line: Consult with your doctor who will help you choose the best fasting option and develop a plan to help you fast safely.
Risks of Fasting With Diabetes
When you fast, you'll probably be hungry (at least at first). Eating fewer calories than you're used to may make you feel drowsy and irritable. Not eating may give you a headache. While these feelings are common and generally harmless, it's important to be aware of the more serious risks of fasting with diabetes. Always talk to your doctor before you make major changes to your diet.
Malnutrition
If you fast for more than a day or so, your body may not get enough of the protein, vitamins, and minerals it needs without supplements. This may lead to malnutrition, a condition that develops when your body doesn't have enough nutrients to stay healthy. Your risk of malnutrition is high if you eat less than 1,200 calories a day long term.
Dehydration
Calorie-free fluids are not restricted in intermittent fasting, so you can drink as much water, diet soda, unsweetened tea, and black coffee as you want. But the risk of dehydration when fasting is high because cutting certain foods from your diet means you're also cutting fluids. For example, soups, yogurt, and fruits like melon, berries, and pineapple are made up of mostly water. So it's important to drink extra fluids to make up for the fluid loss from not eating these water-containing foods.
Some diabetes drugs, especially sodium-glucose cotransporter-2 inhibitors, can make dehydration worse. Make sure to talk with your doctor about your medication plan while fasting to lower your risk of dehydration.
Hypoglycemia
The biggest danger of fasting if you have diabetes is that your blood sugar levels could go dangerously low (a condition called hypoglycemia). That's especially true if you take medication like insulin to control your diabetes. If you don't eat, your blood sugar levels are lower and medication may drop them even more, which can lead to hypoglycemia. Hypoglycemia can cause you to feel shaky, pass out, or even go into a coma.
Hyperglycemia
When you "break" your fast by eating, you may also be more likely to develop too high blood sugar levels. Doctors call this hyperglycemia. This only happens if you eat too many carbohydrates. If fasting prompts you to overeat carbohydrate-rich foods, it may not be the right plan for you.
Before You Try Fasting
Talk to your doctor first. If you have type 1 diabetes, have other health problems due to diabetes, or have had hypoglycemia, your doctor may recommend you not fast.
If your doctor says it's OK to try, ask if you need to check your blood sugar more often or adjust your diabetes medication during and after fasting.
Watch for signs of low blood sugar. If you start to feel shaky, sweaty, or confused, your blood sugar may be too low. Stop fasting right away and do what you normally would to treat hypoglycemia. For example, eat a glucose gel or have a sugary drink followed by a small, balanced meal when your blood sugar level is back to normal.
Be careful about what you eat after fasting. Eating too many carbohydrates after fasting can cause your blood sugar levels to become too high. Choose healthy, balanced meals and snacks.
Use caution. Don't do tough workouts while you're fasting. Hard exercise can make your blood sugar levels dip, which can lead to hypoglycemia. Ask your doctor what activities are OK to do, or just take a break.
Stay hydrated. Having diabetes puts you at a risk of dehydration, which can make your blood sugar harder to manage. Drink lots of water and calorie-free beverages when you fast.
Monitor your blood sugar levels regularly. It's important to regularly monitor your blood sugar levels while fasting to prevent hypoglycemia. When starting your fast, test your blood glucose levels more often to understand how your body reacts to fewer calories. You can also use a continuous glucose monitoring system, a fingerstick-free method way to closely monitor your blood sugar levels. Knowing your blood sugar levels early in your fast may help you predict and avoid hypoglycemia.
Takeaways
Intermittent fasting is a dietary approach that involves eating only during specific periods of the day or week and eating nothing (or much less) the rest of the time. It may be beneficial for people with type 2 diabetes, but more research is needed to prove these claims. If you have diabetes and want to try intermittent fasting, work closely with your doctor to help you choose the most appropriate fasting plan. Before you start your fast, know how often you should monitor your blood sugar levels and how to avoid and manage dehydration, hypoglycemia, and hyperglycemia.
Fasting and Diabetes FAQs
Can diabetes be reversed with fasting?
Some studies show that fasting helps people with type 2 diabetes lose weight and improve blood sugar control, but more research is needed to learn about the long-term effects of fasting and reversing diabetes.
How long should I fast for diabetes?
It's up to you to decide how long you want to fast if you have diabetes. But it's important to make this decision with your doctor to be sure that you're fasting safely. It's especially important to stop your fast when you have hypoglycemia.
Can fasting raise blood sugar?
Fasting does not raise blood sugar, but you may have a sharp rise in blood sugar levels if you eat too many carbs when you "break" your fast by eating.
How long can someone with diabetes go without eating?
There is not a set time at which fasting becomes dangerous if you have diabetes. Instead, your blood sugar levels indicate if you can safely go on without eating. If your blood sugar levels drop dangerously low (hypoglycemia), you need to eat or drink something sugary quickly to avoid passing out or going into a coma. Talk to your doctor before you begin fasting to determine if you can safely do so.
