Types Of Fasting And Their Benefits 

What is fasting?

Fasting is defined as abstaining from food or drink for medical, ritualistic, traditional, religious, or ethical purposes.1 It’s been practiced around the world by various cultures since ancient times. Fasting may either be absolute or partial, and done in either a short duration, a long duration, or in intervals (called intermittent). Its therapeutic use started over 26 centuries ago in ancient Greece, and scientific studies on its physiological effects took fruition in the latter half of the 19th century.1 The metabolic changes and effects occur around 3-5 hours after the last consumption, post-absorption.1

Fasting plays a major role in society to this day. It’s supported by faiths and religions around the world, from pagan religions in the Americas to Islamic Ramadan and periods of Christian fasting. It is advocated by physicians for therapeutic uses, by culturally significant persons, and by people who detest a violation of social, moral, or political values. It is an act that has surpassed time and generations, with various meanings and strong social significance, but it is first and foremost, an issue of health.

The types of fasting and their benefits

A lot of people think that fasting is based solely on time, but that’s not entirely true. There are time-based fasts that involve absolute abstention from any food or drink, intermittent fasting schedules are examples of this. These are very particular with dividing the 24 hours in a day, or the days of the week, following a strict schedule and ratio of time.2 In health and fitness, however, there are three main types of what I like to call “consumption-centered fasting” which also, in one way or another, revolve around the time of the day. This means that both types of fasts overlap. Some of these approaches include Calorie Restrictions, Macro Nutrient Restrictions, and Seasonal Eating.3

Time-based fasting

16:8/20:4 Fasting

These two versions of daily time-based restriction fasting are intermittent and work exactly how you’d expect. The 16:8 ratio lets you eat within 8 hours of a day, and the 20:4 ratio, which is a lot tougher, gives a 4-hour window for consumption. 2

Before we go any further, you might be wondering what Intermittent Fasting can do for the body, so here’s a list of health benefits gained from this type of fasting. 4

  • Positive changes in your hormones, cells, and genes.
  • Weight loss and loss of visceral fat.
  • Reduction of insulin resistance and a lower risk of type 2 diabetes.
  • Reduction of oxidative stress and inflammation in the body.
  • Promoted autophagy, and cellular waste removal.
  • Possible benefits to your heart, brain, and overall longevity.

5:2 Weekly Split

This particular fast is intermittent and is an example of the overlap I mentioned. For two days a week (based on your choice), a person is restricted to around 500-600 calories, providing a rather strict focus on the caloric intake on those given days, and the rest of the 5 days would be free of fasting. 2

24-Hour Fast

This intermittent fast done once or twice a week has been shown to reduce the risk of coronary artery disease (CAD), the fast reduces a substrate that intestinal bacteria produce called Trimethylamine N-oxide (TMAO) which is a risk factor for CAD,5 but we won’t talk about that at length. Since it’s also an intermittent fast over a long period of time it will also deliver the previously mentioned benefits in addition to this spectacular study on CAD.

The main idea is that absolute restraint from any consumption must be done for 24 hours.

36-Hour Fast

This fast is much like the 24-Hour Fast, except that it is primarily abstention from calorie-containing food. Within this period that’s typically done once a week, a person can consume water, black coffee, and herbal tea without additional ingredients.2

36-Hour Fasts according to Amber Sayer,6 have more than a few benefits, including the lowered risk of heart disease and CAD in 24-Hour Fasts. These benefits include:

  • Risk-reduction for metabolic syndrome, heart attack and stroke, inflammation, and various diseases like diabetes, certain cancers, and neurodegenerative diseases.
  • Increase in the production of the human growth hormone, and longevity.
  • Neurogenesis, cell health, and autophagy.

Alternate day Fasting

This fast is performed every other day, with fast days restricted to a single meal of 500 calories, or complete abstention. On non-fasting days, consumption should be normal. This fast is extremely difficult and will most likely not be for the long term. 2

Consumption-centred Fasting

Calorie restriction

Calorie Restriction fasts focus on a diet below the average daily caloric intake. As in some of the intermittent fasts mentioned, diets were subject to a certain number of calories per day (e.g. 500-600 calories, etc.), and the caloric threshold in this fast would ideally be less than your average daily intake.3

A substantial amount of calories must still be consumed in order to avoid malnutrition and other risk factors. Primary benefits include body weight loss and potentially lengthening life.7 Pure abstention and water consumption are done during the designated fasting times, and for an effective fast, it is advised to consume an adequate number of calories beforehand as a means of preparation, depending on the method chosen 3

Macro nutrient restriction

There are three main types of macros: Carbohydrates, Proteins, and Lipids or fats. This particular fast revolves around the absolute or partial cutting of one or two of these three in pursuance of your personal goals. It’s most typically used by athletes, and usually involves a heavier amount of protein disruption. Cutting out protein entirely and consuming only higher-quality sources of fat, carbs, and vegetables provides the gut time to heal.3

Some people interestingly perform fat fasting which involves a high-fat, low-calorie diet that lasts around 2-5 days. This puts your body in a biological state of ketosis (when the body burns fat instead of carbs or sugar) from mimicking abstention from food. It’s beneficial for raising ketone levels in the body and promoting ketosis, but it poses an unhealthy threat, and should only be done short-term.8

It might be worth noting that various types of macro-nutrient restrictions have a number of isolated medical effects. Dr. Eric Berg stresses not intermittently fasting on a high-carb diet, because certain hypoglycemics who consume sugar at a faster rate are endangered by negative neurological and physiological strains.9 If you’re thinking about cutting macros, do your research or seek advice from a professional.

Seasonal Eating

This last type isn’t more of a fast than what a person tends to eat over the course of four seasons, and so I imagine it pertains most endemically to populations in temperate zones, but in truth, it isn’t. It is individualized nutrition based on geography, culture, and the time of the year. In winter, for instance, people might tend to seek fattier foods innately, due to the primal desire to stay warm, but that’s essentially the survivalist nature of humans.

Seasonal Eating could also pertain to holidays and celebrations that occur throughout the year. God’s word in Islam forbids the consumption of blood throughout life, and Islamic traditions in Ramadan forbid any consumption from dawn to sunset. Christian fasting talks about Jesus’ 40 days and nights in the desert without any consumption at all and is considered a holy act throughout the fasting days in the Christian calendar. Halloween lovers might get a bit too much candy, and thanksgiving in America is done with a massive turkey. So, the point to be made here is that your personal and nutritional diet is affected by the seasons and the time of the year.

Risk factors and other concerns

As beneficial as it might seem to fast, there are serious complications that could arise if fasting is done wrong. Due to the lack of fluid received from food and drinks, a lot of people tend to feel dehydrated.10 Dehydration leads to headaches, lethargy, and constipation.11 It is also a precursor to high-stress levels as fasting is a challenging feat. Stress, in addition to dehydration, could couple to make the headaches worse.

Stomach acid is also a major risk factor. Abstention means your stomach is empty at time periods when your body is designed to release acid. If your body isn’t used to the abrupt change, the acid meant for digestion could end up damaging the lining of your stomach or cause heartburn. In vivo models of rats were found to have gastric ulcers after 4 and 6 days after fasting,12 this biological phenomenon can be translated into humans. Simply put, when there is nothing for the acid to break down, it will break down the surrounding area instead.

Certain types of people are prohibited from fasting including individuals with existing eating disorders, underweight individuals, pregnant women, individuals under the age of 18, type I diabetics, and those recovering from surgery.10


How many days should I fast?

The days you designate for fasting must depend on the fasting period that suits you and your goals the best. Your chosen fast, if not traditionally, culturally, or religiously timed, must soundly function well within your schedule, and the level of difficulty you can handle. Your responsibility from then on is to stick with the plan until you’ve reaped the benefits of your fasting!

What can I drink while fasting?

In both calorie-restricted and time-based fasts, consume fluids without additives. Water, tea, and black coffee without all the unnecessary and uncalculated macros should cover your fluid intake, but if you want to stay safe, stick with just water!

In some medical situations, like when blood glucose drops instantly for hypoglycemics, taking fluids with added sugar so as not to completely sacrifice the fast and maintain normal sugar levels is key. Again, it depends on your situation.

What meals should I eat after fasting?

I’d like to think that fasting has certain empirical effects on the body of a person, but it can more powerfully change a person’s mentality. People who start fasting for medical reasons must not revert back to the diets and lifestyles that caused them trouble in the first place. Fasting can teach you strong values like discipline, patience, and self-control.

But if you’re wondering what to eat after fasting, the answer is anything, you have a caloric goal to get yourself back to normal, so reach that goal by consuming whatever you want. However, if a lifestyle change is required for overall better health, practice and work on that instead, adjust your macros.


There are so many types of fasts you can choose from depending on your situation, and the advice that your healthcare professional provides. Time-based intermittent fasts like the 16:8, 20:4 (warrior diet), 5:2 Week Split, Alternative Day Fasts, and the 24 or 36-hour fasts, and the consumption-centered fasts all have individual benefits and respective levels of difficulty. Because every person’s lifestyle and schedule are different — it is your responsibility to find out which fast works for you! (If it isn’t already defined by culture, tradition, or religion).

The health benefits are numerous and rely tremendously on both the type of fast you’ve chosen and your commitment. However, you should consult a professional and do your research, because there are also risk factors involved, especially for individuals with existing medical conditions.


  1. The Editors of Encyclopaedia Britannica. Fasting. In: Encyclopædia Britannica [Internet]. 2019. Available from: https://www.britannica.com/topic/fasting
  2. Lett R. 7 Types of Intermittent Fasting, Explained [Internet]. Span.health. Span; 2019. Available from: https://www.span.health/blog/7-types-of-intermittent-fasting-explained‌
  3.  When to Fast, 3 Different Types of Fasts, and Their Benefits [Internet]. www.opexfit.com. Available from: https://www.opexfit.com/blog/when-to-fast-3-different-types-of-fasts-and-their-benefits#:~:text=There%20are%20three%20main%20types
  4. 10 Evidence-Based Health Benefits of Intermittent Fasting [Internet]. Healthline. 2016. Available from: https://www.healthline.com/nutrition/10-health-benefits-of-intermittent-fasting#TOC_TITLE_HDR_11
  5. Horne B, Cox J, Muhlestein J, Le V, Butler A, May H, et al. 24-Hour Water-Only Fasting Acutely Reduces Trimethylamine N-Oxide: the FEELGOOD Trial. AHA [Internet]. 2018 Apr 27 [cited 2022 Dec 7];130:A13412–2. Available from: https://www.ahajournals.org/doi/abs/10.1161/circ.130.suppl_2.13412
  6. 36 Hour Fasting: Benefits Of A 36 Hour Fast Once A Week [Internet]. marathonhandbook.com. 2022 [cited 2023 Jan 20]. Available from: https://marathonhandbook.com/36-hour-fasting/
  7. Calorie Restriction and Fasting Diets: What Do We Know? [Internet]. National Institute on Aging. [cited 2023 Jan 20]. Available from: https://www.nia.nih.gov/news/calorie-restriction-and-fasting-diets-what-do-we-know#:
  8. West H. What Is Fat Fasting, and Is It Good for You? [Internet]. Healthline. Healthline Media; 2019. Available from: https://www.healthline.com/nutrition/keto-fat-fast
  9. Never Do Intermittent Fasting on a High carbohydrate Diet| Dr. Berg [Internet]. www.drberg.com. [cited 2023 Jan 20]. Available from: https://www.drberg.com/blog/never-do-intermittent-fasting-on-a-high-carbohydrate-diet
  10. Fasting: Health benefits and risks [Internet]. www.medicalnewstoday.com. 2015. Available from: https://www.medicalnewstoday.com/articles/295914
  11. Crosta P. Dehydration: Symptoms, causes, and treatments [Internet]. Medical News Today. 2017. Available from: https://www.medicalnewstoday.com/articles/153363
  12. Matsumoto A, Asada S, Saitoh O, Tei H, Okumura Y, Hirata I, et al. A Study on Gastric Ulcers Induced by Long-Term Fasting in Rats. Scandinavian Journal of Gastroenterology. 1989 Jan;24(sup162):75–8.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Ivan Bernardo

Bachelor of Science in Biomedical Sciences (Hons.) - BSc, University of Chester, England

I am a Published Contributing Writer for HealthCare.PH with a strong domain knowledge in the Life Sciences. I received an award from the University of Chester's Medical School for my dissertation related to Estrogen, with a foundation in endocrinology.

I'm experienced in corporate diversity work, international translation and transcription, the service industry, and medical or health communications/writing.

I am currently taking an online Astronomy course under distinguished Professor Chris Impey at the University of Stanford in a venture to be an all-around scientific mind.

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