- Intermittent fasting (IF) may improve blood sugar levels, A1c, and insulin resistance in type 2 diabetes, though more long-term research is needed.
- If you have diabetes, IF comes with risks like hypoglycemia and is not for everyone, especially those with type 1 diabetes.
- Any fasting diet should be conducted under the supervision of your doctor and dietitian to minimize any complications.
Intermittent fasting (IF) has gained popularity in recent years as a possible tool for improving metabolic health, weight, and several chronic conditions, including type 2 diabetes.
Though long-term data is lacking, many people choose to experiment with IF for diabetes management. If you are considering this type of diet, it is important to consider the increased risk of complications and discuss your plan with your healthcare team.
Continue reading to learn more about intermittent fasting and its potential benefits and risks in type 2 diabetes.
What is Intermittent Fasting?
Intermittent fasting (IF) is a type of eating pattern that focuses on the timing of your food intake rather than specific food choices. There are many variations of IF, but most involve prescribed eating and fasting windows each day or week.
Types of Intermittent Fasting
There are a few main types of intermittent fasting– time-restricted eating, alternate-day fasting, and 5:2 fasting. Though many other variations exist, these plans have been researched the most.
The most common type of IF is time-restricted eating, in which there is a limited window of time each day for unrestricted food intake. This typically involves fasting between 16 and 20 hours per day, though this method has a wide range of fasting times.
Alternate-day fasting (ADF) is when a person fasts every other day, eating normally on the off days. On fasting days, a person may only consume non-caloric beverages, known as 0% alternate-day fasting. Another variation recommends eating 25% of your daily calorie needs on fasting days.
Another popular IF method is 5:2 fasting, which is when a person fasts for two days per week, eating less than 25% of their daily calorie needs on these days. The remaining five days involve regular, unrestricted eating.
Can You Do Intermittent Fasting with Diabetes?
If you have type 2 diabetes, intermittent fasting may be appealing because of its potential metabolic benefits. Though preliminary studies are promising, more research is needed to determine the long-term benefits and risks of intermittent fasting in type 2 diabetes.
Of note, most of the research on diabetes and intermittent fasting is focused on type 2 diabetes, a form of diabetes caused by insulin resistance. Studies on type 1 diabetes are limited.
Close monitoring by a medical professional is important for preventing complications in people with diabetes following intermittent fasting diets. The following information is for educational purposes only.
Effect on Blood Sugar
Preliminary data shows intermittent fasting may help improve elevated blood sugar levels in type two diabetes, though it also increases the risk of blood sugar becoming too low.
In a 2020 review of eight studies on intermittent fasting and blood sugar in type 2 diabetes, researchers found that the IF group had significant improvements in blood sugar levels compared to the control group.
A very small case study in 2018 followed three patients with type 2 diabetes who were on insulin therapy. After following an alternate-day fasting protocol for one month, all three patients could stop taking insulin. They also experienced weight loss and improved A1c levels (a three-month average of blood sugar levels).
Compared to “continuous calorie restriction” or simply following a low-calorie diet daily without fasting, some studies have found that intermittent fasting yields greater improvements in insulin resistance.
While fasting, the body starts primarily burning fat for energy instead of glucose. This change is thought to account for many of IF’s purported benefits. While this shift may benefit weight management efforts, it also may improve the type 2 diabetes disease process.
Some research has linked high body weight and chronic inflammation to the development of insulin resistance, the hallmark of type 2 diabetes. Studies show intermittent fasting may help reduce body fat, appetite, and chronic inflammation.
Potential Drawbacks and Risks
There can be serious risks to intermittent fasting with diabetes, making it essential to discuss your plan with your doctor before starting. The top complications of intermittent fasting in diabetes are:
- Low blood sugar levels (hypoglycemia) during the fasting window.
- High blood sugar levels (hyperglycemia) during the eating window.
- Diabetic ketoacidosis (a dangerous condition more common in type 1 diabetes).
In addition, restrictive fasting diets can increase your risk of disordered eating since they encourage you to ignore your internal hunger and fullness cues. Many people also experience difficulty maintaining the diet along with weight regain after stopping intermittent fasting.
The more restrictive IF diets, such as 0% alternate-day fasting, have a greater risk of complications. Other possible drawbacks and risks to be aware of include:
- Low energy levels.
- Metabolic slowing.
- Increased hunger.
- Vitamin and mineral deficiencies.
Best Types of Fasting for Diabetes
There is not one intermittent fasting diet that has proven to be the most beneficial for diabetes. In general, the best diet for you will be the one you can maintain long-term and that your doctor or dietitian approves of. If you have type 2 diabetes and want to pursue fasting, time-restricted eating is the most flexible and least restrictive method.
A starting point may be fasting for 12 hours per day overnight, with a 12-hour eating window during the day. For example, this may be fasting between 7 p.m. and 7 a.m., with unrestricted eating during the day.
Not only is this a more sustainable option for most people, but it reduces the risk of hypoglycemia since it doesn’t involve fasting for an entire 24-hour period. This method also makes it easier for your doctor to adjust any diabetes medications because you are following the same plan every day rather than alternating days.
Be sure to talk to your doctor before starting any fasting diet for diabetes to help minimize risks and find the best fit for you.
Who Shouldn't Fast?
Fasting diets are not safe for everyone. Specific populations are at a higher risk of developing complications while intermittent fasting, including people with:
- Type 1 diabetes.
- Unmanaged type 2 diabetes.
- History of hypoglycemia.
- Kidney disease.
- History of eating disorder or disordered eating.
- Acute illness.
- Age under 18 or advanced age.
- Compromised immune system.
The safety of intermittent fasting is not well established in people with type 1 diabetes, a form of diabetes caused by a lack of insulin production. This population is at a greater risk of hypoglycemia and diabetic ketoacidosis, a dangerous condition stemming from very high blood sugar levels.
Tips for Fasting Safely with Diabetes
If you have diabetes and would like to explore intermittent fasting, talk to your doctor or dietitian for guidance on how to do this safely. Your doctor may need to adjust your diabetes medications or insulin dosage to prevent hypoglycemia. Depending on your medical history, intermittent fasting may not be recommended for you.
People who are at low risk of developing complications from IF include those who manage their type 2 diabetes through lifestyle alone or who take medications for diabetes but don’t regularly experience hypoglycemia.
If you have decided to try IF, experts recommend conducting a “trial fast,” where you choose an intermittent fasting pattern and follow it for a day, closely monitoring blood sugar levels under the guidance of your doctor. This way, you and your medical team can identify whether or not fasting is safe for you.
In addition, ensure you stay hydrated while intermittent fasting, and choose nutrient-dense foods during your eating windows. Consider scheduling a virtual appointment with a registered dietitian through Nourish for a personalized eating plan.
Studies on intermittent fasting point to reductions in blood sugar and insulin resistance in people with type 2 diabetes. However, adequate long-term data is lacking to make this a standard medical recommendation.
There are numerous risks of intermittent fasting if you have diabetes. If you want to try intermittent fasting, avoid very restrictive plans and talk to your doctor first to make sure you can safely follow the diet.
Managing Diabetes with an RD
There are many evidence-based lifestyle changes for managing diabetes, and it’s essential to ensure these don’t get forgotten with the start of a fasting diet. A nutritionally balanced diet, regular physical activity, and blood sugar monitoring are important lifestyle factors.
For evidence-based nutrition recommendations, try Nourish. We’ll connect you with a top-rate registered dietitian who will work with you to meet your health goals in a sustainable way. Visits are conducted online and are covered by most insurance plans.
Frequently Asked Questions
Most experts recommend people with diabetes eat small, frequent meals, approximately three to four hours throughout the day, to keep blood sugar levels stable. Most fasting diets recommend long fasting windows exceeding these time frames, making it essential to talk to your doctor before starting any intermittent fasting diet with diabetes.
Though more research is needed, small case studies have found that intermittent fasting can lower A1c levels (the three-month average of blood sugars) in people with type 2 diabetes. This is thought to be due to metabolic changes that occur while fasting that impact insulin sensitivity (how well insulin works to deliver sugar to your body for energy).
Less restrictive forms of time-restricted eating are the safest ways to fast if you have type 2 diabetes because they don’t involve fasting for 24 hours at a time. A 12 or 16-hour fasting period overnight is generally considered low risk for individuals with well-controlled type 2 diabetes. However, discussing any fasting plans with your doctor before starting is always important.
Fasting diets are generally not recommended for people with type 1 diabetes due to the risk of hypoglycemia and, in rare cases, diabetic ketoacidosis.
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