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20/4 Intermittent Fasting: All You Need to Know

20/4 intermittent fasting is an advanced version of intermittent fasting. It provides health benefits but also carries some risks.
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20/4 intermittent fasting is an advanced version of intermittent fasting: you fast daily for 20 hours and eat within a 4-hour window. The health benefits are similar to other intermittent fasting methods, but 20/4 intermittent fasting also carries some risks.

Written by
Sarah Neidler, PhD
Freelance Science and Medical Writer

Intermittent fasting has become more and more popular because it provides many health benefits and makes it easier to lose weight. 

There are many different forms of intermittent fasting, including 16/8, 14/10, OMAD, and ADF. 20/4 fasting, also known as the warrior diet, is another intermittent fasting method.

If you’re new to intermittent fasting, you may not have heard of it because it is quite an advanced version. 

What’s special about 20/4 fasting? What are the pros and cons compared to other intermittent fasting methods?

Read on to get the answers to all these questions. 

What is 20/4 intermittent fasting?

20/4 intermittent fasting is a quite extreme, advanced version of intermittent fasting. As the name suggests, you fast daily for 20 hours and eat within four hours.

There are two different variations of 20/4 intermittent fasting: 

1. Warrior diet

Man in a knight's armor.

The warrior diet tries to mimic the diet and lifestyle of ancient warriors, who were battling throughout the day and enjoyed a massive feast in the evening. 

During the 20 hour fasting time, you can eat small snacks like raw fruits and vegetables, small amounts of dairy products, and hard-boiled eggs. In the four-hour eating time, you can eat whatever you want.

The fitness writer Ori Hofmekler created the modern version of the warrior diet in 2001. He claims that this way of eating helped him to stay fit in the Israeli Special Forces.

2. “Clean” 20/4 intermittent fasting

People who follow intermittent fasting tend to adopt a more strict version: They don’t eat anything during the 20-hour fasting time and only consume calorie-free fluids, such as black coffee, tea, or water. 

The eating time window is flexible, although most people choose evening times for practical purposes. 

20/4 intermittent fasting is also very similar to One Meal a Day (OMAD). As the name suggests, you only eat one meal per day on this diet. This meal is usually consumed within 1-2 hours but can also include multiple courses and be extended to four hours. In this case, OMAD would be the same as 20/4 intermittent fasting. 

Benefits of intermittent fasting 20/4

Woman with two half oranges in front of her eyes.

Intermittent fasting provides many health benefits:

  • Facilitates fat loss (1)
  • Can improve brain health (2)
  • Improves cardiovascular health (3)
  • Decreases inflammation (4)
  • Improves blood sugar control (5)
  • Improves gut health (6)
  • Has anti-aging effects (7)

Many of these benefits can be explained by the ability of intermittent fasting to reduce insulin resistance–the underlying cause of diabetes type 2 and a risk factor for many chronic conditions. 

Furthermore, intermittent fasting promotes ketosis and autophagy–two processes that provide many health benefits. Although we won’t go into detail here, you can learn more about this in our articles about autophagy and ketosis. 

Relatively long fasting times are required to promote autophagy and ketosis (8, 9). For this reason, 20/4 intermittent fasting is more potent to stimulate these two processes than other forms of intermittent fasting with shorter fasts (such as 16/8 or 14/10 intermittent fasting).

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Broken red Christmas baubles.

20/4 fasting is an advanced and quite extreme form of intermittent fasting. You should not try it without considerable fasting experience and even then, it may be hard to follow.

Many people also find it difficult to get sufficient nutrients with 20/4 intermittent fasting. When you eat within such a short time window, you automatically eat less. The less you eat, the fewer essential nutrients you take in. For this reason, there is the risk of developing nutrient deficiencies due to a lack of vitamins, minerals, and protein.

Some women are very sensitive to dietary stress. The body senses that now is not a good time to get pregnant, which can result in missed periods and reduced fertility (mostly short-term) (10). 

One further downside is that most people choose to eat in the evening when following 20/4 intermittent fasting. This is mostly for practical reasons–when you’re busy at work, you don’t have time to eat. Consequently, it would be difficult to consume the needed amount of calories, nutrients, and vitamins within a four-hour window during a workday. 

Unfortunately, late-night eating is very unhealthy. Placing the eating window in the late evening may nullify the health benefits of intermittent fasting. 

In one study, participants ate either three meals per day or one meal between 5 pm and 9 pm. After two weeks, the one-meal-group had higher blood sugar in the morning, and after a meal, the blood sugar took longer to get back to normal (11). These results indicate problems with blood sugar regulation, which may increase the risk of Diabetes type 2.

To summarize:

20/4 intermittent fasting

  • Is hard to follow
  • May lead to nutrient deficiencies
  • Can affect female fertility
  • May increase the risk of diabetes when the eating window is late in the evening 

The bottom line

20/4 fasting is an advanced form of intermittent fasting and is not suitable for everyone. It can be challenging to get sufficient nutrients, and it carries the risk of negatively affecting female fertility

Having said this, many people still have very positive experiences with this form of intermittent fasting. 

The health benefits are comparable to other intermittent fasting methods, but it is more potent in stimulating autophagy and ketosis–two crucial fasting-related processes. 

To minimize the risks and maximize the benefits, it can help to combine 20/4 fasting with other forms of intermittent fasting. For example, you may follow 20/4 fasting a few days per week and choose a different intermittent fasting method on the remaining days (e.g., 16/8 intermittent fasting).

If you want to learn more about intermittent fasting, we invite you to join our intermittent fasting community for women only


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2. Phillips MCL. Fasting as a Therapy in Neurological Disease. Nutrients. Oct 17 2019;11(10)doi:10.3390/nu11102501

3. Dong TA, Sandesara PB, Dhindsa DS, et al. Intermittent Fasting: A Heart Healthy Dietary Pattern? Am J Med. Aug 2020;133(8):901-907. doi:10.1016/j.amjmed.2020.03.030

4. Faris MA, Kacimi S, Al-Kurd RA, et al. Intermittent fasting during Ramadan attenuates proinflammatory cytokines and immune cells in healthy subjects. Nutr Res. Dec 2012;32(12):947-55. doi:10.1016/j.nutres.2012.06.021

5. Hutchison AT, Regmi P, Manoogian ENC, et al. Time-Restricted Feeding Improves Glucose Tolerance in Men at Risk for Type 2 Diabetes: A Randomized Crossover Trial. Obesity (Silver Spring). May 2019;27(5):724-732. doi:10.1002/oby.22449

6. Li L, Su Y, Li F, et al. The effects of daily fasting hours on shaping gut microbiota in mice. BMC Microbiol. Mar 24 2020;20(1):65. doi:10.1186/s12866-020-01754-2

7. Wegman MP, Guo MH, Bennion DM, et al. Practicality of intermittent fasting in humans and its effect on oxidative stress and genes related to aging and metabolism. Rejuvenation Res. Apr 2015;18(2):162-72. doi:10.1089/rej.2014.1624

8. Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. May 30 2019;11(6)doi:10.3390/nu11061234

9. Foster DW. Studies in the ketosis of fasting. J Clin Invest. Aug 1967;46(8):1283-96. doi:10.1172/JCI105621

10. Kumar S, Kaur G. Intermittent fasting dietary restriction regimen negatively influences reproduction in young rats: a study of hypothalamo-hypophysial-gonadal axis. PLoS One. 2013;8(1):e52416. doi:10.1371/journal.pone.0052416

11. Carlson O, Martin B, Stote KS, et al. Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women. Metabolism. Dec 2007;56(12):1729-34. doi:10.1016/j.metabol.2007.07.018

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