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What is intermittent fasting?

Intermittent fasting (IF) is a popular diet among people trying to lose weight. Intermittent fasting refers to alternating between times of eating and times of fasting. Often, people will use the 16:8 approach, where they fast for 16 hours and eat during an eight-hour period in a day. 

Diabetes is a chronic health condition with higher risks for complications if you gain weight. There’s a higher risk of hypoglycemia (low blood sugar) with fasting and diabetes, so working on an IF regimen with your doctor is safer.

Is intermittent fasting good for type 2 diabetes?

Several studies have found that IF can be a potential non-medical treatment for type 2 diabetes, with or without weight loss. However, you should always discuss the pros and cons of intermittent fasting with your diabetes care team. Not all medical histories and health conditions are safe for intermittent fasting, so it's vital that you discuss whether it's the right option for you. 

Certain IF regimens boost weight loss. As obesity is one of the most common issues associated with the development and progression of diabetes, losing weight through IF could be very beneficial. One scientific review¹ reported that an average weight loss of 6.7% reduces the incidence of diabetes by 58%.

In people with impaired glucose tolerance/prediabetes, there was a 16% reduction in risk for progression to diabetes for every kilogram of weight lost. 

If you have diabetes, losing just 3% of your weight can improve your fasting blood glucose and hemoglobin A1c. The more weight lost, the greater the benefit, especially if you have a higher BMI. 

How does intermittent fasting work with type 2 diabetes?

According to an academic review,² 24-hour fasting regimens significantly reduced weight and blood glucose in people with diabetes. These diets also led to some patients stopping insulin therapy as their blood sugar was under control. 

Researchers noted that people might struggle with fasting for 24 hours or more. Therefore, they may be better off starting with shorter intervals and time-restricted feeding. They recommended this IF prescription:

  • In week one, fast for 12 hours and feed for 12 hours. Stick with this fasting period until you're comfortable moving to the next phase. The researchers recommend monitoring and logging your daily blood glucose levels so you can send them to your doctor weekly. 

  • Typically starting in week five, you fast for 16 hours and feed for eight hours. The next phase is to increase your fasting period by four hours when you're ready. The report says that you should continue monitoring and logging blood sugar levels. You should also consult a registered dietician to discuss food intake and ensure you're dieting responsibly. 

  • Typically starting in week seven, you fast for 18-20 hours and feed for 4-6 hours. Finally, when you're ready to continue to the next step of the IF process, it is time to add 2-4 more hours to your fasting routine. At this time, the report notes that your doctor should adjust your diabetes medication dosages based on your logged blood sugar readings.

  • Alternate day and periodic fasting options. These aren’t for everyone, and they’re optional. They require 24 or more hours of fasting between feeds, and your diabetic team and dietitian should monitor you closely. The report emphasizes that you should never do this without expert guidance. 

It's important to note that there's a higher risk of hypoglycemia and other potential adverse effects associated with intermittent fasting. This is particularly true in those with poorly-controlled blood sugar. Research also suggests the dieting method has a potential benefit for both types of diabetes.

However, close medical supervision and regular consultations with your physician will ensure you achieve results safely. 

What are the types of intermittent fasting for type 2 diabetes?

A typical fasting period can last anywhere from 12 hours to several days, with the times varying by the regimen. Choosing which type of intermittent fasting is right for you will depend on your medical history and what you can physically and emotionally handle with such a caloric restriction.

The three most common types of IF regimes people use are:

  • Alternate day fasting: Fasting every other day, with days of regularly eating normally in between. On the days you fast, you could consume up to 500 calories.

  • Periodic fasting: One to two fasting days per week (consuming about 500 calories on these days). This method is most successful when you follow the same pattern every week.

  • Time-restricted feeding: Fasting during certain times of the day, often 16-20 hours per day, i.e., 7:00 pm to 11:00 am. 

If intermittent fasting is right for you, discuss the best plan of action with your physician. Your safety and health are a priority when trying to lose weight.

Although there are many ways to IF, some studies show various benefits to time-restricted feeding. One study³ focused on time-restricted feed according to the circadian rhythm. Participants ate most of their calories in the morning and early afternoon.

They saw dramatically lower postprandial insulin levels, improved insulin sensitivity, and better function of insulin-secreting pancreatic cells. There was also lower blood pressure among obese, prediabetic men who participated in time-restricted feeding eating from 7:00 am-3:00 pm.

Another study⁴ on overweight adults with diabetes supported the benefits of time-restricting feeding. It also improves blood glucose, boosts weight loss, potentially lowers the required hypoglycemic drug dosages, and enhances the quality of life. 

Can I do intermittent fasting while on metformin?

According to the National Institute of Diabetes and Digestive and Kidney Diseases⁵ (NIDDK), intermittent fasting is safe if you take a diabetes medication like metformin. However, it depends on the length of time you intend to fast for that day. 

For instance, those who fast for 16 hours and eat for the other 8 hours don’t really need to stop metformin, as it rarely can cause hypoglycemia. The medicine should be in their system for those 6-8 hours while eating, preventing hyperglycemia.

On the other hand, you shouldn't take metformin on the day of intermittent fasting if you intend to fast for the full 24 hours, as it can increase the risks of hypoglycemia. 

What is metformin?

Metformin is an anti-diabetic medication used for the treatment of type 2 diabetes. It comes in brands such as Riomet, Glumetza, Glucophage, Glucophage XR, and Fortamet.

Potential side effects can include:

  • Constipation

  • Heartburn and indigestion

  • Gas

  • Bloating

  • Diarrhea

  • Stomach pain

  • Muscle pain

  • Skin flushing

  • Nail changes

  • Metallic taste in your mouth

  • Headaches

  • There may be effects such as chest pain and rashes in more severe cases. 

  • It can rarely cause lactic acidosis, a serious condition requiring immediate medical care.

What is it for?

Metformin controls how much glucose is in your blood and decreases how much glucose your body absorbs from food. It also influences your insulin response. However, it cannot treat type 1 diabetes. The main issue with type 1 diabetes is the lack of insulin production from the pancreas and not insulin resistance as in type 2 diabetes.

You can take metformin alone or with other medications. It has been the first-line drug for treating type 2 diabetes for decades. It remains the most popular choice because it is affordable, effective at lowering glucose levels, helps with weight loss, and produces few concerning side effects.

Can intermittent fasting cause diabetes?

Although IF can help with type 1 and 2 diabetes in many cases, there's also a concern that the diet might cause diabetes in prediabetic or otherwise healthy people. Continuous fasting can potentially damage insulin, increasing the dieter's risk of developing diabetes.

As type 2 has become an epidemic over the past couple of years, this could be detrimental. The University of Sao Paulo in Brazil conducted an animal study⁶ evaluating the potential risks of intermittent fasting on rats over three months. Although weight loss occurred, long-term IF may damage the pancreas and affect insulin function in healthy individuals. 

Although immediate results can be beneficial for the prevention and treatment of type 1 and 2 due to the reduction in body mass index, there is still a concern for the long-term effects that researchers have not studied as thoroughly. 

It’s important to note that this is a single study conducted on rats and not humans. We need more research to understand if there is any link between IF and diabetes in humans and whether long-term intermittent fasting is safe for those with diabetes. Discuss IF with your primary care doctor or diabetic team before starting the diet to ensure it's safe for you to participate. 

How does intermittent fasting affect type 2 diabetes?

Like most treatments, there are always good and bad effects. While the health benefits can be substantial for some, the risks can be detrimental to others. To ensure this is the right route for you, weigh up the health benefits and risks. 

Health benefits of intermittent fasting for type 2 diabetes

There are many beneficial effects on the management of type 2. According to an academic review,⁷ benefits for patients with type 2 diabetes include:

  • Reducing body weight and body mass index 

  • Decreasing fasting glucose

  • Decreasing fasting insulin

  • Lowering postprandial insulin

  • Lowering insulin resistance by improving insulin sensitivity

  • Decreasing leptin levels

  • Increasing adiponectin levels

  • Reversing the need for insulin therapy 

Other potential benefits may include:

  • Lower blood pressure

  • Lower oxidative stress 

  • Reduced appetite 

  • Increased fatty acid oxidation 

Health risks of intermittent fasting with type 2 diabetes

Just as the popular diet has several health benefits to consider before participating, there are also some health risks worth discussing with your doctor. While not everyone will experience complications, there's always a chance. 

First and foremost, there's the increased risk of hypoglycemia.

A hypoglycemic event refers to the symptoms you experience when your glucose levels fall under the normal range. This is equal to or less than 70 milligrams per deciliter (mg/dL). According to the American Diabetes Association, symptoms can vary from sweating, trembling, and low energy to confusion, rapid heartbeat, and seizures.

In the most severe cases, a patient cannot treat themselves to recover and must rely on someone else to help them. It could even result in unconsciousness or coma.

Although studies⁷ have linked IF to hypoglycemic events in people with type 1, there are also concerns for people with type 2 diabetes. 

According to a 2018 study,⁸ participants with type 2 diabetes on hypoglycemic medications saw an increased rate of hypoglycemia. There were two types of fasting included in the research: two consecutive days of a very low-calorie diet and two non-consecutive days of a very low-calorie diet. The increased rates of hypoglycemia happened even despite decreasing the medication dose. 

However, the researchers concluded that improvements were visible in fasting blood glucose, weight, and quality of life.

Researchers reported medication-induced hypoglycemia as the most immediate health risk in another intermittent fasting study.⁹ However, it wasn’t the only risk mentioned:

  •  Long-term intermittent fasting can cause protein malnutrition in patients who aren’t aware of how much protein they’re eating.

  • Adverse effects associated with insufficient energy and dehydration such as:

    • Dizziness

    • Nausea

    • Insomnia

    • Syncope

    • Falls

    • Migraines

    • Weakness

    • Excessive hunger pangs

Tips for intermittent fasting with type 2 diabetes

If you and your doctor decide you're safe to begin intermittent fasting to achieve a healthier weight with type 2 diabetes, some tips can help you be safe and successful. These recommendations will help you avoid hypoglycemia and other risks while benefiting from the many advantages of safely participating in intermittent fasting. 

Monitor blood sugar levels

Regularly monitoring your blood sugar levels is necessary if you have diabetes. However, it becomes much more critical if you decide to start intermittent fasting. It's common for your blood glucose to fluctuate during fasting periods and after. If you have type 1 or 2 diabetes, you’re at a higher risk of hypoglycemia and hyperglycemia (high blood sugar) during these fluctuations.

Monitor energy levels

In most cases, intermittent fasting increases energy levels among dieters because they’re using fat for energy. Fat is slower to digest and continuously boosts your energy instead of the many cycles your metabolism will go through under normal eating. If you notice you're more tired and your energy levels are low, this could be a sign that your blood sugar is low.

Balance your carbohydrates

Eating a balanced diet of carbohydrates between fasting cycles is an excellent way to prevent high blood sugar levels. Since your body breaks carbs down into glucose, balancing proteins and vegetables with starchy carbs during feeding periods can be beneficial. Eating too many carbs or simple carbs (like refined sugar) can spike your blood sugar. 

Check your mood

Irritability and confusion are common signs that your blood sugar is low. By checking in on your mood throughout your experience, you may notice you’re more irritable than usual. Take a self-monitored blood glucose test to ensure your numbers are still in the normal range.

If so, you may be experiencing a change in mood from hunger, which should subside within days or weeks. 

However, if your glucose results are too high or too low, follow the plan you and your doctor created. Consult your doctor immediately if you notice a sharp drop in your glucose level or experience hypoglycemic events, even if you think it’s not serious. 

The lowdown

Intermittent fasting can be a great non-medical treatment for type 2 diabetes since it improves insulin sensitivity and reduces weight. However, medical supervision is essential since the diet can be potentially unsafe for some patients, both with and without diabetes. 

If you are currently taking metformin to control your glucose levels, research shows it is safe to continue taking the medication when you start intermittent fasting. However, you shouldn’t take the drug if you fast for an entire day as it could increase the risk of hypoglycemia. Otherwise, there are few risks associated with hypoglycemia when fasting only for 12-16 hours.

The medicine will still be in your system for 6-8 hours when eating to prevent hyperglycemia. 

Stay in touch with your healthcare provider, monitor your blood sugar and energy levels, check your mood, and balance carbohydrates during eating. These steps can reduce some serious risks associated with the diet.

Have you considered clinical trials for Type 2 diabetes?

We make it easy for you to participate in a clinical trial for Type 2 diabetes, and get access to the latest treatments not yet widely available - and be a part of finding a cure.

Joining community groups and exercise programs for my condition made me feel empowered – but I want to be part of finding a cure.
Peter, 64

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