What is Intermittent Fasting?

Curious about intermittent fasting? Read this article to learn what the definition is and how to do it properly.
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The definition of intermittent fasting is when you purposely don’t consume any calories for a certain period of time. This dietary trend is widely popular due to its many health benefits and ability to help individuals lose body fat.

Written by
Christine Richardson, PhD
Clinical Project Manager at Becton Dickinson

Intermittent fasting is one of the most popular diet trends that involves switching between periods of eating and fasting.

The reason why this diet is so popular is because it helps people regain control of their health while helping them feel more energized.

In this article, we discuss the definition of intermittent fasting and how it could help you.

Definition of Intermittent Fasting?

What is the definition of intermittent fasting? Intermittent fasting is the choice to refrain from consuming any food or calorie-containing beverages for a defined period of time. 

People claim to like this diet because it’s easier than counting calories. With intermittent fasting, you don’t have to count your calories, you just have to eat everything in a certain timeframe.

Intermittent Fasting History

A pile of old books.

In order to understand the definition of intermittent fasting, let’s first discuss its history. While fasting has recently become popular, this dietary strategy has been used for years for spiritual development and health purposes.

For example, the ancient Greeks believed that consuming food increased one’s risk of demonic possession, making fasting a common practice. 

Another good example is Ramadan. Ramadan is a 28-30 day fast where Muslims refrain from eating or drinking from sunrise to sunset. Ramadan is still widely practiced and you might know someone who partakes in this fast.

Fasting has also been used for political protest. It is known that Gandhi fasted at least 14 times as a means of peaceful protests. 

Individuals of the Irish Republican Army also used fasting as political protests. Some members fasted from 45-61 days(1)!

Discover our selection of intermittent fasting books by clicking here.

Forms of Intermittent Fasting

There is no clear cut definition of intermittent fasting with regard to your eating schedule because there are many variations of this dietary pattern. Some of the most popular forms of intermittent fasting include alternate-day fasting, whole-day fasting, and time-restrictive eating where individuals decrease the window that they allow themselves to eat each day. 

A popular version of time restricted feeding is the 16/8 diet where individuals fast for 16 hours straight each day and eat freely for the remaining 8 hours.

Time restricted feeding is probably the most popular form of fasting because it consists of extending the overnight fast you do when you’re asleep. 

How Will You Feel While Fasting?

A big concern of people who have never tried intermittent fasting is how they will be successful at it. Most of us like to eat when we are hungry-sometimes it’s all we think about-and sometimes don’t feel well when we go long periods of time without food.

Honestly, the first couple days or even couple weeks may be a little difficult. It will take time for your body to adjust. 

But after you adjust, people claim to not feel hungry during their fasting hours and also report having more energy and better mental clarity(2). 

If you decide to try fasting and are struggling during your fasting window, try drinking more water and/or tea (with no sweetener or milk) to help with feelings of hunger.

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What to Eat While Fasting

Meat, salad, bread and a dip on a plate.

What you eat during your eating window can really dictate what fasting can do for you. 

To elaborate, if you eat nothing but energy-dense and nutritionally void food in your eating window, you may not see any changes at all…and you can still gain weight.

However, if you eat nutritionally dense, whole foods like fruits, vegetables, whole grains, and lean meats, you will likely see many beneficial changes. Don’t get us wrong, there’s a time and place for everything (including cake and ice cream)...it’s about balance.

Now you may be wondering what you can consume during your fasting window and the short answer is: anything that doesn’t contain any calories – water, tea, black coffee.

The long answer is: it depends. Some people will still consume some food during their fasting window, especially if the fasting window is very long. For example, some individuals practice modified alternate day fasting where they eat one small meal (about 250-500 calories) on their fasting days. 

While this choice is entirely up to you, choose wisely. If you decide to try a fasting routine where the fast isn’t very long, like the 16/8, you should definitely aim to fast throughout the entire window. 

Why Fast?

Many studies have shown that intermittent fasting is a great strategy to implement to become a healthier version of yourself

These studies show that fasting can help people lose body fat while decreasing their risk for various metabolic conditions like inflammation, hypertension, type 2 diabetes, and more.

Other studies show that fasting helps increase autophagy, which can decrease your risk of neurodegenerative disorders like Alzheimer’s and Parkinson’s disease, cancer, along with slowing down the ageing process(3,4).

In short, intermittent fasting is great for your overall health. Find out why intermittent fasting work by reading our dedicated article.

The Bottom Line

Intermittent fasting is a popular diet used to lose body fat and decrease one’s risk of other metabolic conditions.

Check out our intermittent fasting ultimate guide to give you more information on your fasting journey.

If you are thinking of trying intermittent fasting or if you already are, join our community of women who are all experimenting with intermittent fasting! Being a part of a group will help with the transition into fasting…you don’t have to be on this journey by yourself!

Cheers to a happier and healthier you!


1. Kerndt PR, Naughton JL, Francisco S, Driscoll CE, Loxterkamp DA. The history, pathophysiology and complications (Medi-cal Progress). West J Med. 1982;137:379–99. 

2. De Toledo FW, Grundler F, Bergouignan A, Drinda S, Michalsen A. Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects. PLoS One [Internet]. Public Library of Science; 2019 [cited 2021 Jun 19];14. Available from: /pmc/articles/PMC6314618/

3. Fujikake N, Shin M, Shimizu S. Association between autophagy and neurodegenerative diseases [Internet]. Frontiers in Neuroscience. Frontiers Media S.A.; 2018 [cited 2021 Jun 9]. p. 255. Available from: /pmc/articles/PMC5972210/

4. Martinez-Lopez N, Tarabra E, Toledo M, Garcia-Macia M, Sahu S, Coletto L, Batista-Gonzalez A, Barzilai N, Pessin JE, Schwartz GJ, et al. System-wide Benefits of Intermeal Fasting by Autophagy. Cell Metab [Internet]. Cell Press; 2017 [cited 2021 Jun 9];26:856-871.e5. Available from: /pmc/articles/PMC5718973/

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