Is Intermittent Fasting Good To Do If You Have Diabetes?
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Medically reviewed by Kelly Wood, MD
Intermittent fasting is a way of eating that cycles periods of fasting, or completely abstaining from calories, with periods of normal calorie intake. Intermittent fasting has risen in popularity over the years, and research regarding its efficacy is ongoing. At this time, research about intermittent fasting specifically for people with diabetes is relatively sparse, but some of the existing studies are positive and some are negative.
Here’s what you need to know about intermittent fasting if you have diabetes, including how effective and safe the dietary approach really is.
Here at Health, we know how important it is to share the experiences of those living with chronic conditions. We asked Health's diabetes advocate Alysse Dalessandro to share some topics frequently discussed by those within the diabetes community, which led to the creation of this article.
What Is Intermittent Fasting?
Intermittent fasting is an overarching term that’s used to describe eating patterns that involve regularly occurring periods of fasting or very low calorie intake. While most normal eating patterns involve an overnight fast while you’re sleeping, people following intermittent fasting regimens intentionally restrict their calorie intake in order to reap the health benefits associated with fasting.
Intermittent fasting is used for various reasons, including to support weight loss and improve certain aspects of metabolic health, such as levels of your blood lipids (fat), cholesterol, and triglycerides. Intermittent fasting has also been shown to help with blood sugar and hemoglobin A1c (A1c), a measurement of your average blood sugar over the past three months.
Traditional methods of fasting involve completely abstaining from calories during the fasting window. Modified intermittent fasting regimens allow for a small amount of calories to be consumed during the fasting window, which is usually less than 25% of normal calorie intake.
Types of Intermittent Fasting
There are several types of intermittent fasting, each with its own set of guidelines. Although each type is different, all intermittent fasting methods involve periods of fasting (traditional methods) or significant calorie restriction (modified methods).
A few of the most common types of intermittent fasting include:
Time-Restricted Feeding (TRF)
TRF is a traditional approach to intermittent fasting. When following TRF, you’ll take in all your calories within a specific period of time and then fast for the remainder of the day.
For example, the 16/8 method of intermittent fasting—which is one of the most common and most studied forms of intermittent fasting—involves fasting for 16 hours out of the day and consuming all of your calories within an eight-hour window. Other types of TRF involve longer or shorter fasting windows.
TRF is associated with a number of health benefits, including reducing blood sugar levels and promoting weight loss.
Alternate-Day Fasting (ADF)
Traditional ADF is more restrictive than TRF as it involves fasting for a full day before a day of regular eating. People following traditional ADF completely abstain from calorie intake during the 24-hour fast, while people following modified alternate-day fasting consume a small amount of calories during fasting days, restricting their calorie intake to just 25% of their calorie needs.
ADF has been shown to be effective for reducing blood sugar and blood lipid levels. ADF can also improve insulin resistance, making it so your cells respond to insulin so they can better absorb glucose from your blood.
Periodic Fasting
Periodic fasting differs from TRF and ADF as it can be implemented as frequently as a couple times per week or as little as once a month. There are several types of periodic fasting methods, including the 5:2 method, which is a popular type of periodic fasting in which a person eats normally five days out of the week and then fasts for two. Fasting days can be either consecutive or nonconsecutive.
Periodic fasting can either be traditional, which involves complete abstention from calories during fasting periods, or modified, which allows for small amounts of calories to be consumed during fasting windows.
Like other types of intermittent fasting, periodic fasting has been linked to several health benefits, such as weight loss and improved blood sugar.
How Intermittent Fasting Can Affect Diabetes
Intermittent fasting is a relatively new phenomenon in the world of diet plans. Therefore, more research is needed to determine how it can affect people with diabetes. Preliminary studies have been conducted, but the body of research is small and inconclusive.
It's unclear if intermittent fasting is more effective for managing diabetes compared to more traditional dietary modifications such as continuous energy restriction (when you restrict your calorie intake each day so that you take in about 25% below your energy requirements). A 2021 review of five studies demonstrated that intermittent fasting and continuous energy-restricted diets had similar effects on glycemic control, including changes in A1C and fasting blood sugar levels, among people with type 2 diabetes.
Frequently Asked Questions
Current Research Is Mixed
There is a common misconception that missing a meal will lead to lower blood sugars since meals raise your levels. This has made intermittent fasting recommended for people living with type 2 diabetes; however, scientifically studies are mixed. Some show that this can have the opposite effect, as the body's stress response to being hungry raises levels.
In my experience, eating regular meals is actually better for blood sugar levels.
Potential Benefits
As long as you're using safe methods and are under the guidance of your healthcare provider, following an intermittent fasting regimen could be helpful if you have diabetes. Research shows that intermittent fasting can improve several aspects of health among people with type 1 and type 2 diabetes, including:
Reduced blood sugar
Improved fat metabolism (the breakdown of dietary fats)
Improved insulin sensitivity (because cells are more effective at absorbing blood sugar, you don't need as much insulin)
Improved weight management
Improved body composition (the percentage of bone, muscle, organs, water, and fat in your body)
Reduced inflammation
Intermittent fasting may also help reduce the risk of low blood sugar (hypoglycemia) among people with type 1 diabetes.
One reason intermittent fasting can have such positive effects is because the approach to eating reduces your calorie intake. This reduction in calories can support fat loss and reduce blood sugar and blood lipid (fat) levels. Another reason intermittent fasting can be beneficial for people with diabetes is because, during fasting, the body meets its energy needs by breaking down the storage form of glucose, called glycogen, and stored fat, which results in lower insulin levels.
The benefits of intermittent fasting on type 2 diabetes might last in the long term. A 2023 randomized control trial that included 46 people with type 2 diabetes taking insulin found that participants who followed an 18-hour fast three days a week for 12 weeks experienced a significant reduction in A1C compared with those who did follow the diet. There were no reports of severely low blood sugar levels among the people who followed the diet.
Potential Downsides
Historically, it has been recommended that people with diabetes eat regular, balanced meals (without skipping meals) to help keep blood sugar levels stable. If your healthcare provider recommends weight loss as part of your diabetes management, there are more ways to do this without potentially facing side effects from intermittent fasting such as:
Dizziness: If your blood sugar drops too low, you may become lightheaded or dizzy.
Headaches: Headaches are another common reaction to low blood sugar and are a commonly reported side effect of intermittent fasting.
Excessive hunger: Being excessively hungry can trigger a stress response in your body, causing you to release the stress hormone cortisol, which can raise blood sugar levels.
Potential hormone dysregulation: While more studies are needed on this subject, preliminary studies have found that intermittent fasting can cause disruptions in your body's hormone production, including insulin.
Most research suggests that as long as medication is properly managed, people with type 2 diabetes can safely use intermittent fasting methods, such as time-restricted eating, without the risk of significant safety issues. That said, more research is needed before experts can make definitive recommendations regarding the safe use of intermittent fasting in the treatment of diabetes. Also, issues such as low blood sugar, dizziness, and fatigue can arise if diabetes medication isn’t properly managed or if unsafe fasting methods are used.
Intermittent fasting can come with more risk for those with type 1 diabetes. Research shows that prolonged fasting is associated with an increased frequency of severe low blood sugar among people with type 1 diabetes. That said, this potential risk can be minimized by monitoring blood sugar levels and adjusting medication accordingly.
It’s also important to note that some intermittent fasting methods, especially those that involve longer fasting periods, can cause side effects like dizziness, headaches, and extreme hunger.
If your healthcare provider recommends weight loss as part of your diabetes management, there are more ways to do this without potentially facing these side effects.
If you have diabetes and are interested in using intermittent fasting, it’s important to speak with your healthcare team to assess safety and identify potential risks. Keep in mind that while some people with diabetes may benefit from fasting, it’s not safe or appropriate for everyone.
Tips for Intermittent Fasting With Diabetes
If you’re interested in incorporating intermittent fasting into your wellness routine, the first thing you should do is talk to your healthcare provider. Although intermittent fasting may offer health benefits for some people with type 1 and type 2 diabetes, it’s not the right choice for everyone.
Your healthcare provider can share more information about intermittent fasting, including potential benefits and risks, and can provide specific recommendations for safe fasting methods based on your health needs and medical background.
Start Slow
If your healthcare provider is comfortable with you trying intermittent fasting, it’s best to start with a method that involves shorter fasts—especially if you’re not used to going long periods without eating. For example, if you usually eat within an 11-hour window, try decreasing that window to nine hours, and see how you feel. If you’re successful with shorter fasting windows, you can try increasing your fasting times to see how your body reacts.
Work With Your Provider to Adjust Medications
Keep in mind that your medication might have to be adjusted, especially if you’re taking insulin. Your healthcare provider may also recommend you wear a continuous glucose monitor or regularly check your blood sugar levels when fasting to ensure your blood sugar remains at a safe level.
If you're engaging in intermittent fasting with diabetes, it's essential to monitor for signs of low blood sugar, such as a rapid heartbeat, dizziness, extreme hunger, and confusion and to have a plan to treat low blood sugar should it arise.
Prioritize Nutrients
One of the more convenient qualities of intermittent fasting is that there are no specific food rules to follow. Some people choose to combine dietary patterns such as low-carb diets or paleo diets with fasting, but there are no rules as to what you can and can't eat during your non-fasting hours.
That said, it’s always best to consume a nutrient-dense diet high in protein and fiber. This would mean prioritizing vegetables, legumes, nuts, and other foods known to support healthy blood sugar levels.
A Quick Review
Intermittent fasting is a way of eating that cycles periods of fasting with periods of normal eating. Research shows the dietary approach may be a safe and effective method for improving blood sugar control and other aspects of health among people with type 1 and type 2 diabetes, but more research is needed at this time.
While intermittent fasting can be helpful for some people with diabetes, it’s not a safe or appropriate method for everyone. If you're interested in trying it, speak with your healthcare provider first. They can discuss what the specific benefits might be for you and whether the popular way of eating is the right choice for you.
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