Intermittent fasting is a type of eating pattern that involves periods of voluntary fasting. There are various methods, which vary in terms of the permitted eating hours.

Many people believe that intermittent fasting can aid weight loss and offer other health benefits.

This article looks at whether this eating pattern might be beneficial for people living with type 2 diabetes.

Intermittent fasting (IF) is an eating regimen that cycles between periods of eating and periods of voluntary fasting or very low calorie intake. Researchers believe that IF leads to a metabolic switch from the use of glucose as the primary energy source to the use of fat.

IF also has a positive effect on the circadian rhythms of both gut biology and the release of insulin and growth hormone. In these ways, it improves energy metabolism and weight regulation.

There are several methods of intermittent fasting, which involve fasting for different periods:

Time-restricted feeding

This type of IF involves eating during only a certain number of hours each day. A popular plan is the 16:8 method, which requires a person to fast for 16 hours and eat during an 8-hour window.

Alternate day fasting

People following this pattern alternate between a “fast day,” when they consume no or minimal calories (up to 500), and a feasting day, when they can eat as much as they want.

Periodic fasting

This type of fasting involves no or minimal calorie intake for 24-hour periods. Examples are the 5:2 diet and Eat Stop Eat.

With the 5:2 method, a person eats normally on 5 days of the week and then eats about 500 calories during each of the 2 fasting days, which should not be consecutive.

People adhering to the Eat Stop Eat regimen have to refrain from food and calorie-containing drinks for an entire 24-hour period once or twice a week. They should then eat “responsibly” on the other days of the week, rather than treating them as feast days.

The majority of IF research has involved animals rather than human participants. The evidence to support health improvements in people is promising, but many of the clinical studies to date have been relatively short-term interventions over a period of months.

A 2018 review article showed that nearly all IF studies resulted in some degree of weight loss, ranging from 2.5% to 9.9%, and associated fat mass loss. However, there is little research to prove that IF is superior to other diets and eating patterns in promoting weight loss.

The use of an IF diet may also have a beneficial effect on blood pressure. In one study, researchers observed 1,422 people for 1 year while they followed a fasting program. The participants experienced a reduction in both systolic and diastolic blood pressure.

In another study, which involved adult males, researchers found that IF provided metabolic and cardiovascular benefits, such as a decrease in total cholesterol and low-density lipoprotein (LDL) cholesterol.

Scientists know that insulin resistance improves with calorie restriction. After a period of fasting, insulin sensitivity increases, and insulin levels decrease. These changes result in improved blood sugar levels both during fasting and shortly after eating.

IF can have various health benefits for people with diabetes. These include:

  • promoting weight loss
  • improving insulin sensitivity, leading to lower insulin requirements
  • normalizing fasting blood glucose levels
  • reducing hemoglobin A1c levels

Many people with type 2 diabetes also have metabolic syndrome, hypertension, or hyperlipidemia. IF may improve these metabolic parameters.

IF can produce various side effects, such as:

  • dizziness
  • nausea
  • insomnia
  • syncope
  • falls
  • migraine headaches
  • weakness that limits daily activities
  • excessive hunger pangs

Having a chronic disease such as diabetes may increase a person’s risk of experiencing many of these adverse events.

There is also a risk of hypoglycemia in people with type 2 diabetes, especially those who are taking insulin or medications such as sulfonylureas. This risk is lower with other diabetes medications, but it still exists.

Dehydration is a risk as well. Even though a person can consume calorie-free liquids on “fasting days,” unless they drink additional fluids, dehydration can occur.

Dehydration can then lead to hypotension. On fasting days, people may need to reduce or completely stop some medications. These include diuretics, antihypertensives, and diabetes medications that can lead to dehydration, such as SGLT-2 inhibitors.

However, it is essential never to stop taking a medication or change the dosage without speaking with a doctor first.

In one small case series, three men were able to reverse their insulin resistance due to IF, allowing them to maintain control of their blood sugar levels even after ceasing insulin therapy. In addition, they experienced weight loss, a reduction in waist circumference, and a decrease in hemoglobin A1c levels.

However, as relapse of diabetes is a possibility, it is more accurate to say that these individuals are in remission.

In another study, the Diabetes Remission Clinical Trial (DiRECT), the researchers randomized the participants to one of two groups: weight management or pharmacological therapy. They found that 46% of the participants in the weight management group achieved diabetes remission.

Still, the research to date remains limited, and further studies are necessary.

IF may worsen symptoms in people with hard-to-control blood sugar levels and those with brittle diabetes.

There is minimal research on the effects of IF in certain populations, such as people who are pregnant or lactating.

People at higher risk of developing side effects such as hypoglycemia, dehydration, and hypotension should also avoid IF. These individuals include older adults, those with immunodeficiencies, and those with a history of traumatic brain injury or dementia.

Deliberately engaging in fasting can also exacerbate the challenges that people with eating disorders face.

A person with diabetes should consult their doctor before starting IF to ensure that it is safe for them. A person will also need their doctor’s guidance on adjusting the dosages and timing of their medications to reduce the risk of hypoglycemia.

Individuals trying IF should check their blood sugars more frequently — ideally, every 2–4 hours — especially when first starting out.

People with hypoglycemia should break their fast immediately and treat their low blood sugar with 15 grams of carbohydrates in the form of glucose tablets or gels. They should consult with a doctor before restarting the fast.

It is also important to drink additional fluids during the fasting period to reduce the risk of dehydration and hypotension. A doctor may recommend stopping or reducing the dose of some diabetes medications, diuretics, and antihypertensives.

People should maintain a balanced diet on nonfasting days and avoid processed, fatty, and sugary foods. Doing so will mean that they do not reverse the positive effects of the fasting days.

There are a few diet takeaways from the science of IF. Insulin sensitivity changes with a circadian rhythm, decreasing throughout the day and into the night. Therefore, meals that a person consumes at night are associated with higher glucose and insulin levels.

Liming the hours of eating to a time earlier in the day — for example, selecting an 8-hour window between 7 a.m. and 3 p.m. or even 10 a.m. and 6 p.m. — is effective in boosting metabolism and aiding in weight loss.

People should also try to avoid eating and snacking shortly before going to bed. Not snacking between meals will facilitate the metabolic switch from the use of glucose for energy to the use of fat.

A balanced diet is also important, so people should avoid sugars and processed carbohydrates, focusing instead on eating fruits, vegetables, whole grains, lean meat, and healthy fats.

Perhaps the most important factor, though, is that people choose an eating plan that they can sustain in the long term.

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Dr. Kelly N. Wood, M.D., is an internal medicine physician who is board certified in Endocrinology, Diabetes, and Metabolism. She earned her medical degree from The University of the West Indies in Barbados before relocating to the United States in 2006. Dr. Kelly is currently in clinical practice in Atlanta, GA.