Intermittent Fasting and Diabetes: Benefits and Risks

Historic photo of long dining tables set with empty plates — Photo: Levick, Edwin (1869-1929) via Wikimedia Commons (Public domain). Image credits

Last reviewed: October 9, 2026 · Sources: CDC, NIH/NIDDK, American Diabetes Association

Intermittent fasting has become a popular approach to eating, and many people with diabetes or prediabetes wonder whether it could help them. Some research suggests intermittent fasting can support weight loss and improve blood glucose for some people. But fasting also carries risks for people with diabetes, especially those who take insulin or medicines that can cause low blood glucose. This guide explains what intermittent fasting is, what is known about its effects, the risks, and how to talk with your care team if you are considering it.

Important: If you have diabetes, do not start fasting without talking with your health care team first, especially if you take insulin, sulfonylureas, or other medicines that can cause low blood glucose. Medicine doses often need to be adjusted.

What is intermittent fasting?

Intermittent fasting is an eating pattern that cycles between periods of eating and periods of not eating or eating very little. It focuses more on when you eat than on what you eat. Common approaches include:

Time-restricted eating: Eating all meals within a set window each day, such as 8 to 10 hours, and fasting for the remaining hours. A common example is eating between 10 a.m. and 6 p.m.
Alternate-day fasting: Alternating between days of normal eating and days of fasting or eating very few calories.
The 5:2 approach: Eating normally five days a week and greatly reducing calories on two non-consecutive days.
Periodic longer fasts: Fasting for 24 hours or longer occasionally. These carry more risk and are generally not recommended for people with diabetes without close medical supervision.

Religious fasting, such as during Ramadan, also involves long periods without food or drink and requires careful planning for people with diabetes.

What does research show?

Research on intermittent fasting in people with diabetes is growing but still limited, and many studies are small or short. Some findings:

Intermittent fasting can lead to weight loss, mainly because people tend to eat fewer total calories.
In some studies, intermittent fasting led to weight loss and improvements in blood glucose that were similar to, but not clearly better than, standard calorie reduction.
Some people find a structured eating window easier to follow than counting calories; others find it harder.

The American Diabetes Association's Standards of Care emphasize that there is no single best eating pattern for everyone with diabetes and that the best approach is one a person can sustain safely, in partnership with their care team. NIDDK's guidance on eating and physical activity for weight management also highlights finding an approach you can maintain over time.

Potential benefits

For some people, intermittent fasting may:

Help reduce total calorie intake and support weight loss. See weight and diabetes.
Reduce late-night snacking, which may help overnight and morning glucose for some people. See the dawn phenomenon.
Simplify eating routines.

These benefits depend on the individual and on what foods are eaten during eating periods.

Risks for people with diabetes

Low blood glucose (hypoglycemia)

This is the biggest concern. If you take insulin or medicines that increase insulin release, such as sulfonylureas or meglitinides, going without food can cause glucose to drop dangerously low. Doses usually need to be reduced or timing changed during fasting periods. See hypoglycemia.

High blood glucose and DKA

Some people overeat when the fasting period ends, leading to high glucose. People with type 1 diabetes who reduce insulin too much during fasting risk diabetic ketoacidosis. People taking SGLT2 inhibitors may also have a higher risk of ketoacidosis during prolonged fasting. See hyperglycemia and DKA.

Dehydration

Some fasting practices, including religious fasts, limit fluids as well as food. Dehydration can raise glucose and strain the kidneys.

Other concerns

Fasting may not be appropriate for people with a history of eating disorders.
Fasting is generally not recommended during pregnancy or breastfeeding, or for children and teens. See diabetes and pregnancy planning.
Older adults, people with kidney disease, and people with frequent lows or hypoglycemia unawareness may face higher risks. See diabetes in older adults.
Some medicines need to be taken with food.

If you and your provider decide to try it

Work with your care team on a plan that includes:

Medicine adjustments: Which doses to reduce, skip, or move, and when.
Glucose monitoring: Check more often, especially during fasting periods and after breaking a fast. A continuous glucose monitor can be very helpful. See checking blood sugar and CGMs.
When to stop the fast: Clear thresholds, such as glucose below 70 mg/dL or above a level your provider sets, or symptoms of feeling unwell.
Hydration: Drink water and other calorie-free fluids during fasting periods unless your fast restricts them.
Healthy eating windows: Focus on vegetables, lean proteins, high-fiber carbohydrates, and healthy fats, and avoid overeating. See diabetes-friendly eating basics.
Activity timing: Be careful with exercise during fasting periods, which can increase the risk of lows.
Starting gently: Many people start with a modest eating window, such as 12 hours overnight, before considering anything longer.

Religious fasting

People with diabetes who wish to fast for religious reasons should meet with their care team well before the fasting period to assess risk and plan medicine changes, monitoring, and when to break the fast for safety. Many religious traditions provide exemptions from fasting for people whose health could be harmed.

Alternatives that also work

If fasting isn't right for you, other approaches can also improve glucose and support weight loss, such as the plate method, carb counting, Mediterranean-style eating, or lower-carbohydrate eating. See low-carb diets and diabetes and carb counting.

Frequently asked questions

Is intermittent fasting safe if I have type 2 diabetes and take only metformin?

Metformin alone rarely causes low blood glucose, so the risk of lows is lower, but you should still talk with your provider before starting.

Is skipping breakfast the same as intermittent fasting?

It can be a form of time-restricted eating, but simply skipping meals without a plan can lead to overeating later or, if you take certain medicines, low blood glucose.

Can I drink coffee during a fast?

Many people drink black coffee or unsweetened tea during fasting periods. Adding sugar or cream adds calories and carbohydrates.

Will fasting cure my diabetes?

No eating pattern cures diabetes. Some people who lose significant weight can bring glucose into the normal range, but ongoing monitoring is still needed.

Can intermittent fasting cause headaches or dizziness?

Some people experience headaches, hunger, irritability, or dizziness, especially at first. In people with diabetes, dizziness or shakiness may signal low blood glucose, so check your glucose and treat a low if needed.

Should I exercise while fasting?

Exercise during a fasting period can increase the risk of lows, particularly for people taking insulin or sulfonylureas. Ask your care team about timing activity and what to eat or carry with you.

Where can I find more reliable information?

Trusted sources include the CDC, NIDDK, MedlinePlus, and the American Diabetes Association. Be cautious with social media posts or products that promise quick fixes, and check new information with your care team before making changes.

Key takeaways

Intermittent fasting focuses on when you eat, with patterns like time-restricted eating or the 5:2 approach.
It may help some people lose weight and improve glucose, but it is not clearly better than other approaches.
People taking insulin or sulfonylureas face a real risk of low blood glucose and need medicine adjustments.
Never start fasting without a plan from your care team.

Sources

Links to the sources cited above appear in the text. We rely on the Centers for Disease Control and Prevention (CDC), the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), and the American Diabetes Association (ADA).

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