3 Day Fast Guide: What Is a Three-Day Fast, and How Do You Do It?

A three-day fast is considered a prolonged fasting diet. Any duration of fasting greater than 48 hours is considered a prolonged fast.

To do a three-day fast, you fast from food and calorie-containing beverages for a consecutive 72-hour duration. Fasting for 72 hours can be intimidating and hard to complete. You can work your way up to fasting for 72 hours if you need to. For example, you could practice with a 24-hour fast first and see how well your body tolerates fasting.

You can begin your three-day fast at any time of the day after any meal. For example, you may choose to start your fast after dinner on a Monday at 6 PM. In this case, your fast would end on Thursday at 6 PM. Or, you may choose to begin your fast after you eat breakfast on Friday at 8 AM. In this case, your fast would continue until Monday at 8 AM. Completing a three-day fast is flexible for your schedule. You may choose to do it when you have a busy work week so that your mind stays occupied, or you may decide to do it on a weekend when you have more time to relax and meditate. Planning the schedule for a three-day fast is entirely up to you.

When planning the last meal you eat before you begin your fast, make sure to eat a nutritious meal before you start your fast in order to provide your body with nutrients.

When you are fasting, you are not allowed to eat food or drink anything that contains calories. You are allowed to drink water, black coffee, and tea, as they are naturally calorie-free. While fasting, you should drink at least three liters of water every day to maintain hydration [1].

When you end your fast, it is important not to binge eat. Your body will need time to adjust to receiving nutrients again and complete the metabolic shift from utilizing fat as fuel to once again using glucose for fuel. You can ease yourself back to eating a regular meal by beginning with vegetable juices, bone broth, or other lower-calorie nutrient-dense meals.

Benefits of Three-Day Fasting

Weight Loss

The main reason people want to do a three-day fast is for the weight loss benefits.

When your fast reaches 48 hours, your body enters into a starvation state [2]. It no longer depends on glucose as fuel, and your body is in a state of ketosis. Being in a state of ketosis means that your body begins to use fat for fuel instead of glucose [2]. The fat stored in adipose tissues consists of approximately 85% of the available calories in the body that can be used for fuel [3]. When your body uses fast as fuel, it breaks down body fat, resulting in body composition changes and weight loss [12].

Many studies show that fasting from food for over 24 hours will cause weight loss and loss of body fat [2, 3, 4, 5, 6, 8, 10, 11, 12]. The average amount of weight loss recorded was 0.9 kg ( 2 pounds) per day during the first week of fasting. This means that fasting for 72 hours may result in up to 6 pounds of weight loss.

One study observed that the metabolic shift to using fat as fuel resulted in an increased resting energy expenditure, which results in weight loss [4]. Another study found that the increased amount of ketones in the body helped reduce appetite, resulting in weight loss [5].

While many factors contribute to weight loss during fasting, the most common factor of weight loss during fasting is due to calorie restriction. Any time you restrict calories and consume less than your body needs to maintain its current weight, you most likely will experience weight loss [13].

Improved Cardiovascular Health

Many studies show that fasting can improve cardiovascular health [6, 10, 12]. They have observed that fasting can help regulate blood pressure and decrease heart rate [6, 10, 12].

Fasting overall can decrease cardiovascular disease risk as it improves the risk factors for cardiovascular disease [12]. Fasting can result in weight loss, improved insulin resistance, regulated blood pressure, improved resting heart fate, and help resist cardiac muscle damage. Each of these factors can decrease the risk of an individual developing cardiovascular disease.

Disease Prevention

Fasting may aid in disease prevention. Studies have found that fasting reduces metabolic stress, oxidative stress, inflammation, and damage to DNA . Prolonged fasting may also increase cellular resistance to stress, toxins, and disease [7, 9, 12]. It can also improve the body’s activation and regeneration of immune cells [7]. Each of these factors decreases the chance of developing chronic diseases.

Current research shows promise that fasting can promote cancer prevention [7, 8]. However, research is still limited in human studies [7, 8].

Insulin Regulation

Many studies show that fasting for over three days may improve glucose metabolism, increase insulin sensitivity, and decrease insulin resistance [8, 10, 12]. The metabolic shift that the body goes through, from using glucose as fuel to using fat as fuel, decreases the body’s circulating glucose and insulin by 30% [8].

These studies show promise that fasting can prevent the development of type 2 diabetes for those with risk factors for developing type 2 diabetes.

Improved Cognition

Some research shows that fasting may improve cognitive performance [10, 12]. However, research is not strong enough to claim these effects yet, and more research needs to be done [12].

Slows Down Aging

The effects of fasting, such as limiting oxidative damage to cells, reducing inflammation, increasing cell metabolism, regulating glucose, and improving insulin resistance, may potentially slow down the aging process [8, 12].

Risks of 3-Day Fasting

While there are many benefits of three-day fasting, there are many risks that need to be taken into consideration. Even though a longer fasting period may sound more beneficial than a shorter fast, it is not necessarily better for you [14].

Fasting for three days may result in side effects such as headaches, nausea, fatigue, indigestion, and hunger [11, 16]. Rare, more serious effects could occur, such as gout, uric acid stones, low blood pressure, and heart arrhythmia [3].

Children and women who are pregnant or breastfeeding should avoid fasting diets as they need to consume regular calories for growth [14, 15].

Those with a history or risk of developing eating disorders should also avoid fasting diets, as fasting can increase an unhealthy fixation on food [14, 15].

Individuals who have been diagnosed with type 2 diabetes should avoid fasting diets [6, 14, 15]. Since fasting restricts food, it can cause low blood sugar, which can be dangerous for those with type 2 diabetes [6, 14, 15].

FAQs

Is it healthy to fast for three days?

There are many benefits of fasting, but some risks to consider. For healthy individuals, who are not underweight, fasting is generally healthy and will only cause very minor side effects such as headaches, nausea, fatigue, and hunger due to calorie restriction.

What happens during a three-day fast?

When you do a three-day fast, your body undergoes a metabolic shift from using glucose as fuel to using fat as fuel, which places you in a state of ketosis. This metabolic shift has many benefits, from weight loss and fat loss to decreased blood pressure and improved insulin resistance.

What should I do when fasting for three days?

When you fast for three days, you do not eat any food or calorie-containing beverages. This may be difficult to do as we are accustomed to consuming three meals a day plus snacks. You can plan your three-day fast on any consecutive days that work for you. It may be best to avoid fasting on days that you need to engage in increased physical activity, as fasting can cause fatigue and nausea. Plan to do it on days that you would be physically resting and do things that can help occupy your mind to help avoid thinking of food when hungry.

Do you lose weight on a three-day fast?

Yes, experiencing weight loss on a three-day fast is very likely. Most studies have found that individuals lose an average of 2 pounds per day during the first week of fasting due to calorie reduction and being in ketosis.

How do you break a three-day fast?

When ending your three-day fast, you should gradually reintroduce food to your body. Binge eating a meal after fasting will only cause your insulin to spike and cause digestion discomfort. It is a good idea to ease your digestive system back from a fast by eating bone broth, vegetable juice, or other low-calorie, nutrient-dense foods.

Wrapping Up

There are many benefits of three-day fasting, but there are risks to consider as well. Most fasting diets over 24 hours produce similar results, and fasting for a longer duration may not be better for you and may increase risks [8, 14].

Fasting for three days may be very hard to complete due to increased hunger [11].

Studies caution that fasting for over 72 hours should only be completed under medical supervision due to possible risks [8]. If you are looking into doing a three-day fast, it would be important to consult with medical professionals before starting. You would want to make sure that your body is healthy enough to tolerate fasting for three days. You should also talk to a medical professional if you experience any side effects and possibly end your fast to prevent extreme adverse reactions.

References

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2. Stockman, M. C., Thomas, D., Burke, J., & Apovian, C. M. (2018). Intermittent Fasting: Is the Wait Worth the Weight? Current Obesity Reports, 7(2), 172–185.
3. Kerndt, P. R., Naughton, J. L., Driscoll, C. E., & Loxterkamp, D. A. (1982). Fasting: the history, pathophysiology and complications. The Western journal of medicine, 137(5), 379–399.
4. Zauner, C., Schneeweiss, B., Kranz, A., Madl, C., Ratheiser, K., Kramer, L., Roth, E., Schneider, B., & Lenz, K. (2000). Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. The American Journal of Clinical Nutrition, 71(6), 1511–1515.
5. Wilhelmi De Toledo, F., Grundler, F., Sirtori, C. R., & Ruscica, M. (2020). Unravelling the health effects of fasting: a long road from obesity treatment to healthy life span increase and improved cognition. Annals of Medicine, 52(5), 147–161.
6. Scharf, E., Zeiler, E., Ncube, M., Kolbe, P., Hwang, S. Y., Goldhamer, A., & Myers, T. R. (2022). The Effects of Prolonged Water-Only Fasting and Refeeding on Markers of Cardiometabolic Risk. Nutrients, 14(6), 1183.
7. Buono, R., & Longo, V. D. (2019). When Fasting Gets Tough, the Tough Immune Cells Get Going—or Die. Cell, 178(5), 1038–1040.
8. Longo, V., & Mattson, M. (2014). Fasting: Molecular Mechanisms and Clinical Applications. Cell Metabolism, 19(2), 181–192.
9. Cheng, C. W., Adams, G., Perin, L., Wei, M., Zhou, X., Lam, B., Da Sacco, S., Mirisola, M., Quinn, D., Dorff, T., Kopchick, J., & Longo, V. (2014). Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression. Cell Stem Cell, 14(6), 810–823.
10. Washburn, R., Cox, J., Muhlestein, J., May, H., Carlquist, J., Le, V., Anderson, J., & Horne, B. (2019). Pilot Study of Novel Intermittent Fasting Effects on Metabolomic and Trimethylamine N-oxide Changes During 24-hour Water-Only Fasting in the FEELGOOD Trial. Nutrients, 11(2), 246.
11. Johnstone, A. M. (2007). Fasting? the ultimate diet? Obesity Reviews, 8(3), 211–222.
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13. Redman, L. M., & Ravussin, E. (2011). Caloric Restriction in Humans: Impact on Physiological, Psychological, and Behavioral Outcomes. Antioxidants & Redox Signaling, 14(2), 275–287.
14. Johns Hopkins Medicine. (2022, March 7). Intermittent Fasting: What is it, and how does it work? Harvard: School of Public Health. (2022, May 17). Diet Review: Intermittent Fasting for Weight Loss. The Nutrition Source.
15. Finnell, J. S., Saul, B. C., Goldhamer, A. C., & Myers, T. R. (2018). Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting. BMC Complementary and Alternative Medicine, 18(1).

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