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Types of Intermittent Fasting

by Markita Lewis, MS, RD September 24, 2021 5 min read

 alarm clock inside refrigerator

If you’ve been looking for ways to step up your health and wellness routine, you may have heard about intermittent fasting. There isn’t a “one-size-fits-all” approach to fasting, so understanding the different types of intermittent fasting may help you decide if it’s right for you.

What is Intermittent Fasting?

Intermittent fasting is an eating pattern that involves cycling between periods of eating and abstaining from food.

It’s different from other popular fad diets by not requiring any restrictions on the types of food that you eat and unlike some diets, intermittent fasting has a body of research that can back its health benefits.

Benefits of Intermittent Fasting

Research on intermittent fasting shows that this dietary pattern may have a number of benefits for the body.

Fasting promotes autophagy (ridding the body of damaged cells), reduces oxidative and metabolic stress, modifies metabolism, helps regulate our circadian rhythms and may benefit the health of our gut microbiota.

2020 review on the benefits of fasting found that time-restricted eating and alternate-day fasting were effective for reducing risks to heart health by lowering weight, decreasing blood pressure, improving blood lipids and potentially improving insulin sensitivity.

Small studies suggest that intermittent fasting may help weight loss and blood glucose management in people with unhealthy blood sugar levels.

Recent reviews suggest that intermittent fasting and time-restricted eating patterns are as effective as calorie-restriction in promoting weight loss and loss of body fat.

Limited evidence suggests that intermittent fasting may even help improve your mood.

Now onto the major types of intermittent fasting that people may follow:

Time Restricted Eating

If you’re looking to get started with intermittent fasting, time-restricted eating, also known as time-restricted feeding, is a great place to start. It is the fasting method that does not require you to spend more than 24 hours on a fast, nor does it require any days of calorie-restricted eating.

When starting out, you may want to try a 12:12 method (which is fasting for 12 hours, then eating during a 12-hour window) or a 14:10 window (fasting for 14 hours, then eating within a 10-hour window). Once you have gauged your tolerance for fasting, you can expand your choices for fasting.

16:8 intermittent fasting is one of the most popular forms of intermittent fasting that people follow. This method is especially popular amongst people trying to lose weight, but individuals looking for general health benefits and weight management can also benefit from a 16:8 pattern.

20:4 intermittent fasting is an extra challenge, fitting your calorie intake into only 4 hours. Some people choose to have a single, large meal during this time period. Alternately, you can schedule your meals so that you have one big meal and one small meal within the 4-hour window.

Alternate Day Fasting/Monk Fast

Alternate Day Fasts (ADF) is a method of intermittent fasting that involves fasting for an entire day, then eating during a 12-hour window. This creates approximately a 36-hour fasting window where you can either only drink noncaloric beverages or a calorie-restricted diet of approximately 500 calories.

One variety of ADF is the Monk Fast, in which you have a strict 36-hour water fast, followed by a 12-hour eating window. This particular fast is done only once a week, so some people may prefer to do this because it isn’t a long commitment.

One Meal A Day (OMAD)

One-meal-a-day fasting (OMAD) is an intense form of fasting in which all of your food intake for the day is restricted to a single hour.

The research on whether OMAD could be more effective for health than dietary patterns that allow more frequent meals is inconclusive.

A 2020 review on the impact of meal frequency found that eating once a day was the most beneficial for reducing body weight, but it didn’t have any particular benefit for reducing fat mass or changing calorie intake compared to eating more frequently.

There may be some negative consequences of eating once daily. In a 2009 study comparing eating only one meal/day compared to three meals/day, those who followed the one meal/day pattern experienced greater hunger, unhealthy blood pressure, higher cholesterol (total, LDL, and HDL) and other altered lab values compared to those who ate three times/day.

24-Hour Fasts

Doing a 24-hour fast is exactly what it sounds like. You start your 24-hour fast after your last meal for the day, and you can start eating at the same time the following day. During your fast, you are only allowed to have calorie-free beverages.

There is no requirement for which meal you choose as your starting and stopping point for your fast. That means that if breakfast is what keeps you going throughout the day, you can choose to start your fast during breakfast.

A 24-hour fast is typically done only once or twice per week (in an Eat-Stop-Eat method), and it is very similar to 5:2 intermittent fasting or ADF.

5:2 Fasting Method

The 5:2 method is a popular intermittent fasting method that allows you to eat normally for 5 days out of the week, and fast for only two days. It’s strongly recommended that your two days of fasting are non-consecutive to make this pattern easier to follow.

On your fasting days you can either choose to do a water fast, or limit your calories to either 25% of your usual intake or about 500 calories.

Making the Most of Your Fast

When you’re doing your fast, there are a few tips to help you have the most success with your fast:

  • Drink extra water: When you’re fasting, you’re not getting additional fluids from the foods you eat so pay extra attention to hydrating throughout the day.
  • Focus on nutrient-dense foods: Restricting your time available for eating may reduce your chances for getting enough nutrients throughout the day. To support either weight loss or general health, focus your diet on whole foods.
  • Eat regularly: During your eating window, do not try to skip meals. Eating at regular intervals helps you eat enough calories, nutrients, and helps with feelings of hunger.

Fasting and Safety

When you’re fasting, it’s important to know your limits. It may be normal to experience a few side effects when transitioning to an intermittent fasting pattern, but long-term symptoms are a sign that there is something wrong.

Either your fasting cycle is too long, you’re not drinking enough water during your fasts, or perhaps you’re not eating enough during your feasting windows.

Some serious side effects include stomach discomfort, vomiting, weakness, hair loss, negative mood, food obsessions, headaches, dizziness and significant GI distress. If you have these symptoms long-term while fasting, stop your current fast and speak with your doctor about your symptoms.

People with certain health issues or taking certain medications may not be able to fast safely. Before starting your fast, consult with your doctor to see if intermittent fasting is appropriate for you and  discuss your optimal fasting window.

About the Author

 Markita Lewis, MS, RD
Markita Lewis, MS, RD

Markita has an interest in the biological, social and cultural aspects of eating. She enjoys writing about nutrition and wellness, food justice and policy, cultural food ways and the psychology of nutrition. You can find her at

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