Fasting has been a part of several cultures through generations. Although fasting traditionally was done for spiritual purposes, an increasing number of people are now fasting for weight loss and other health benefits.
While there are several fasting methods prevalent today, the overwhelming options often make it difficult to pick one. Some popular fasting methods include intermittent fasting (IF), water fasting (WF), and keto OMAD.
In intermittent fasting, you eat and fast during specific windows. A water fast is a step ahead of IF as it involves complete calorie restriction for a specific duration, which could be hours or days. So, if you plan to take a water fast challenge, you must forgo food and all caloric beverages for the set duration. (1)
Water fast can be kept for 12 hours, 24 hours, 48 hours, and so on, depending on your fitness goals. Nonetheless, I recommend choosing a fasting method that aligns well with your health objectives, current medical conditions, and lifestyle.
As a medical practitioner, I have tried several fasting methods, including a water fast. As I was used to the 16:8 IF, the 24-hour water fast didn’t seem too difficult. However, if you are scouting options on long water fasts, such as a 21-day method, I recommend you to check out the stages of water fasting to know more about how this fasting works and how to prepare your body to avoid unwanted problems.
My experience of choosing an appropriate water fast involved spending hours reading and analyzing scientific research papers. This article is a comprehensive 21-day water fast guide. I will also share the right way of doing the fast and explain its pros and cons.
This article covers the mechanics of a 21-day water fast, the preparatory steps for such a prolonged fast, the benefits associated with a three-week water-only fasting period, and the potential risks involved in an extended water fast.
What is a 21 Day Water Fast?
A 21-day water fast is where you abstain from food and all caloric beverages for 21 consecutive days or three weeks. During such a fast, you can only drink plain water.
A 21-day water fast is a prolonged fast that keeps your body in starvation for a considerable time to detoxify and trigger cell repair with autophagy. A long fast as this one needs preparation and may not be suitable for everyone. Let’s see what are the things you should consider before commencing a 21-day water fast.
How To Prepare For a 21 Day Water Fast?
For those new to water fasting, embarking on a 21-day water-only fast right away may not be a safe choice. Here are a few things you can consider when preparing for a prolonged fast such as this.
Start with a Short Duration
A 3-week water fast is an extreme form of fasting. Such long fasts should be done under medical supervision. You should keep a regular check on how your body responds to the long fasting duration and whether or not you should continue it.
Consult a Health Professional
Prolonged fasts may not go well with everybody. Pregnant women or those with severe medical conditions should avoid prolonged fasts.
It would be wise to consult a medical professional for guidance and advice, especially if you have any pre-existing or underlying health conditions. This will help you rule out the risks of long fasts and know if it is ideal for you.
Plan your Diet Pre and Post-Fast
Regulate your diet before undertaking a long fast. Dietary amendments such as choosing healthier food options and avoiding refined, sugary, deep-fried, and ultra-processed foods before beginning the fast can go a long way in achieving the desired efficacy.
It is not just the fasting period that contributes to your weight loss goals but also the diet you follow and the lifestyle you maintain post-fasting. Make sure to maintain a healthy diet even after the three weeks. Planning your meals before and after a fast is crucial to ensure you consume healthy food that aligns with your fitness objectives.
Planning your meals will also help you avoid overeating or binge eating after a fast. Mindful eating holds a lot of importance in a prolonged fast. Eating recklessly after a long fast can lead to regaining all the weight you loose.
Break your fast with easily digestible food. Avoid carb-rich food and heavy meals when breaking a water fast. When you return to your normal diet after a 21-day fast, always start with small portions. You can choose steamed veggies, fruits, or healthy fasting juice recipes.
During a prolonged fast, your digestive system enters a resting phase and may take some time to return to a fully functional routine. Thus, your body may take at least a few weeks to return to a regular diet.
Prolonged fasts are not just about physical preparation; you need to be equally strong mentally to keep up with an intense three-week fast. Going without food for 21 days may not be too difficult when done correctly, but it does need a strong determination to sail through the journey successfully.
As water is the only source of nourishment for your body during a water fast, make sure you drink plenty of water throughout the fast.
You can also add non-caloric electrolyte supplements to prevent dehydration. Electrolytes can keep your body replenished with essential minerals throughout the fast. This will prevent acute dehydration. Some studies indicate that dehydration from fasting can increase lipid concentrations. (2)
Know the After-Effects of Fasting
A 21-day-long water fast can have some side effects, such as headaches, insomnia, and hunger pangs. Some individuals may experience fainting or other health issues such as low blood pressure or a fall in blood glucose levels.
Regardless of whether you are new to prolonged fasts or have experience with them, it’s essential to stay attuned to your body’s signals that suggest it’s time to end the water fast.
Benefits of a 21 Day Water Fast
Let’s take a close look at what you can gain from a prolonged fast:
- Increased sensitivity to tastes like sweet and salty in a way that may reduce preference for such foods and increase consumption of healthier foods. (3)
- Support weight loss and improve cardiometabolic risk factors. (4)
- Promotes autophagy and cellular renovation. (5)
- Reduces oxidative stress and related health issues. (6, 7)
- Increases the human growth hormone. (8)
- Lower the risks of neurodegenerative diseases. (9)
- Reduces inflammation and age-related diseases. (10)
Pitfalls of a 21 Day Water Fast
While longer water fasts may offer some benefits, prolonged fasts, such as 21 days, aren’t risk-free. Here are some of the shortcomings of a three-week water fast that you should know about before giving it a go.
Changes in Renal Function
Some studies reveal that water fasting slightly decreased renal function, although it maintained the standard reference values as per studies. (11)
Research shows that extended fasting, ranging from five to 20 days, can have mixed effects on the human body. While it promotes muscle protein breakdown as part of weight loss, this could pose long-term health concerns. (12)
The same study also suggested that prolonged fasts could bring greater glycemic control and a decrease in LDL cholesterol and triglycerides.
Prolonged fasting with only water can result in electrolyte imbalance and dehydration. As your body solely relies on water during this time, not drinking adequate water can lead to losing essential minerals such as sodium, magnesium, and potassium.
Low Blood Pressure
Prolonged water fasting can result in a decrease in both systolic and diastolic blood pressure. While it could benefit those trying to manage high blood pressure, extended water fasting could be dangerous for people with low blood pressure.
Can I lose weight by doing a 21-day water fast?
Like many other calorie and time-restricted diets, water fasting can help you lose weight. This weight loss, however, is more likely to come from lean muscle loss than fat loss. However, you should know that prolonged water fasting can come with a few health risks, such as muscle loss, drop in blood pressure levels, electrolyte imbalance, headaches, nausea, and fatigue.
Are there any alternate fasting methods that can help weight loss?
Yes, many fasting methods can help in weight loss. One such popular and sustainable method is intermittent fasting. IF comes with fewer risks than extended water fasts. You can choose an intermittent fasting pattern like alternate day fasting or a 5:2 diet to achieve your weight loss goals.
What beverages can I drink during my 21-day water fast?
Ideally, you should stick to drinking only plain water throughout the fasting period. Consuming water is indispensable as it is the primary source of nourishment for your body for 21 days. However, you may add a reliable non-caloric electrolyte supplement to water to ensure electrolyte balance. All other caloric beverages must be avoided, or you will break your fast.
A 21-day water fast is an extreme fasting method, which can be safe under medical supervision. However, such prolonged fasts are not suitable for everyone. Choosing a three-week water fast may depend on various factors, including your medical history and existing health conditions.
With water fasting, your body relies solely on water as the only external source of nutrients for 21 days. This increases the risk of water-mineral imbalance in the body, which could result in medical conditions stemming from low mineral levels such as sodium and potassium.
Moreover, water fasting can increase uric acid levels in the body and could alter your taste buds. Despite many drawbacks, a three-week-long water fast does have its pros.
I would suggest my readers check all the fasting options available before starting with one. Choosing intermittent fasting or shorter, alternate-day water fasts can be a practical option that fits seamlessly with your daily routine.
Also, repeating long water fasts frequently may be unsafe as you may end up depriving your body of nutrients, causing deficiencies. Moreover, your body may take time to return to its normal appetite.
If you still want to give the 21-day water fast a try, make sure to take all the necessary precautions and consult a qualified medical professional for guidance before starting. Preparing physically and mentally before you begin your 21-day water fast will ensure better results.
- Attinà, A. et al. (2021) ‘Fasting: How to Guide’, Nutrients, 13(5), p. 1570. Available at: https://doi.org/10.3390/nu13051570.
- Dehydration during fasting increases serum lipids and lipoproteins. (1994, December 1). PubMed.
- Myers, T.R. et al. (2022) ‘Potential Effects of Prolonged Water-Only Fasting Followed by a Whole-Plant-Food Diet on Salty and Sweet Taste Sensitivity and Perceived Intensity, Food Liking, and Dietary Intake’, Cureus [Preprint].
- Scharf, E. et al. (2022) ‘The Effects of Prolonged Water-Only Fasting and Refeeding on Markers of Cardiometabolic Risk’, Nutrients, 14(6), p. 1183.
- Bagherniya, M. et al. (2018) ‘The effect of fasting or calorie restriction on autophagy induction: A review of the literature’, Ageing Research Reviews, 47, pp. 183–197.
- ‘Fasting reduces oxidative stress, mitochondrial dysfunction and fibrosis induced by renal ischemia-reperfusion injury’ (2019) Free Radical Biology and Medicine, 135, pp. 60–67.
- Johnson, J.B. et al. (2007) ‘Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma’, Free Radical Biology and Medicine, 42(5), pp. 665–674.
- Salgin, B. et al. (2012) ‘The effect of prolonged fasting on levels of growth hormone-binding protein and free growth hormone’, Growth Hormone & IGF Research, 22(2), pp. 76–81.
- Gudden, J., Arias Vasquez, A. and Bloemendaal, M. (2021) ‘The Effects of Intermittent Fasting on Brain and Cognitive Function’, Nutrients, 13(9), p. 3166.
- Zhou, R. et al. (2021) ‘The influence of fasting and caloric restriction on inflammation levels in humans’, Medicine, 100(15), p. E25509.
- Mojto, V. et al. (2018) ‘Effects of complete water fasting and regeneration diet on kidney function, oxidative stress, and antioxidants’, Bratislava Medical Journal, 119(02), pp. 107–111.
- Ezpeleta M, Cienfuegos S, Lin S, Pavlou V, Gabel K, Varady KA. Efficacy and safety of prolonged water fasting: a narrative review of human trials. Nutr Rev. 2023 Jun 27:nuad081. doi: 10.1093/nutrit/nuad081. Epub ahead of print. PMID: 37377031.