Get Smarter About Your Diet

Get the 5-minute weekly newsletter keeping thousands looking, feeling, and performing at their best.

Join thousands of faith-focused, fitness-minded men and women. You’ll get the Nikkola Newsletter each Monday and Thursday, filled with insights, tips, and articles that’ll strengthen your body, mind, and resolve.

The Truth About Water Fasts: Good, Bad, and Alternatives.

Water fasting has become a buzzword in the world of health and fitness. It makes headlines, is the focus of online challenges, and has plenty of social media influencers framing it up as a “health hack.” But is it a miracle cure-all, an overhyped fad, or something in between?

In today’s society, where quick fixes are often sought after but seldom effective, it’s crucial to separate fact from fiction.

This article aims to provide you with a comprehensive, science-backed look into the practice of water fasting. We’ll delve into its history, the underlying physiology, and the potential benefits and risks. We’ll also take a look at the popular belief that water fasting is a powerful detoxifying solution, and offer some practical alternatives for those who find water fasting too extreme or risky.

Oh, and if you were wondering, I do not recommend multiple-day water fasts for reasons that should soon be obvious. However, there are plenty of people interested in doing one.

Whether you’re contemplating your first fast or are a seasoned faster looking for more information, this article is your go-to guide for understanding the truth about water fasting.

History of Fasting

Fasting is far from a modern-day concept. In fact, it’s one of the oldest therapeutic practices known to mankind, deeply rooted in various cultures and religions. From the Biblical accounts of Jesus fasting in the desert to the sacred Islamic practice of Ramadan, fasting has been heralded for its spiritual and physical benefits for millennia.

In recent years, however, fasting has made a resurgence, not just as a religious or cultural practice, but as a scientifically-backed approach to improving health. Modern-day fasting is often stripped of its spiritual origins, rebranded under various names like intermittent fasting, time-restricted eating, and of course, water fasting. But whether it’s an ancient ritual or a 21st-century health trend, the core concept remains the same: abstaining from food for a period of time to achieve a specific outcome.

What Is Water Fasting?

Water fasting is a form of voluntary food deprivation where one abstains from all forms of food and caloric beverages, consuming only water for a set period. Unlike other forms of fasting, where certain foods or some calories may still be allowed, water fasting is more restrictive. It aims to bring the body into a state where it relies on stored fat and other reserves for energy, rather than incoming food.

There are different types of water fasting, each with its own set of rules and durations:

  1. Short-Term Water Fasting: Lasts for 24 to 72 hours and is generally considered safe for most healthy adults.
  2. Extended Water Fasting: Goes beyond 72 hours and should only be done under medical supervision.
  3. Periodic Water Fasting: Involves shorter fasts done repeatedly over a longer period, like once a week or once a month.

While water fasting may seem extreme to some, it’s essential to understand how it differs from other types of fasting. Unlike intermittent fasting, where eating windows and fasting periods are defined but caloric intake is not restricted, water fasting requires complete abstinence from calories. This results in a deeper fasting state, triggering unique physiological responses.

The Science Behind Water Fasting

Understanding the physiological changes that occur during water fasting is crucial for grasping both its benefits and risks. When you abstain from food, several processes kick in to sustain your body’s energy requirements.

  1. Glycogen Depletion: Initially, your body taps into glycogen stores in the liver and muscles for energy. However, these stores are limited and deplete within about 24 hours.1Cahill, G. F., Jr. (2006). Fuel metabolism in starvation. Annual Review of Nutrition, 26, 1-22.
  2. Ketosis: As glycogen stores run out, the body starts breaking down fats to produce ketones, a secondary source of energy.2Veech, R. L. (2004). The therapeutic implications of ketone bodies: the effects of ketone bodies in pathological conditions. Prostaglandins, Leukotrienes and Essential Fatty Acids, 70(3), 309-319.
  3. Autophagy: This is a cellular cleansing process that gets activated under stress conditions like fasting. It involves the breakdown and recycling of damaged or dysfunctional cellular components.3Levine, B., & Klionsky, D. J. (2004). Development by self-digestion: molecular mechanisms and biological functions of autophagy. Developmental Cell, 6(4), 463-477.

While these processes are complex, the takeaway is that water fasting puts the body into a unique metabolic state that can bring about various health benefits, which we’ll discuss in the following sections.

Is Water Fasting Good for Detox?

The widespread promotion of water fasting as a powerful de­toxification method is prevalent, particularly within alte­rnative health communities. However, it begs the question: What does scientific evidence show about its effectiveness?

First, it’s essential to understand what “detox” means. In a medical context, detoxification refers to the removal of harmful substances, usually overseen by healthcare professionals. Your liver and kidneys are naturally equipped to filter out toxins and waste products from the body.4Liska, D. J., Lyon, M., & Jones, D. S. (1998). Detoxification and biotransformational imbalances. Explore (NY), 2(2), 122-140.

The belief that water fasting accelerates detoxification often stems from the idea that fasting induces a deeper state of autophagy, thereby helping the body “cleanse” itself. While autophagy does help in cellular cleanup, there’s limited evidence to suggest that water fasting significantly enhances the body’s natural detoxification processes.5Levine, B., & Klionsky, D. J. (2004). Development by self-digestion: molecular mechanisms and biological functions of autophagy. Developmental Cell, 6(4), 463-477.

It’s worth noting that extended water fasting could actually be counterproductive for detoxification. The liver and kidneys require certain proteins and micronutrients to function optimally in detoxification pathways.6Hodges, R. E., & Minich, D. M. (2015). Modulation of Metabolic Detoxification Pathways Using Foods and Food-Derived Components: A Scientific Review with Clinical Application. Journal of Nutrition and Metabolism, 2015, 760689. Extended fasting periods can deplete these essential nutrients, potentially impairing the body’s natural ability to detoxify.

While water fasting may offer various health benefits, labeling it as a powerful detoxifying solution is an overstatement, at least according to current scientific understanding.

Read also: Do Detox Diets Work?

Benefits of Water Fasting

Water fasting has gained popularity not just as a weight-loss strategy, but also for its purported health benefits. Let’s delve into the science-backed advantages:

  1. Weight Loss: One of the most obvious benefits is weight loss, primarily due to calorie restriction. Studies have shown that water fasting can result in significant weight loss, although it’s essential to follow a healthy, high-protein diet afterward to maintain the results.7Varady, K. A. (2011). Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?. Obesity Reviews, 12(7), e593-e601. You must also remember that much of the weight loss comes from emptying your digestive tract, from water loss, and some muscle loss. Remembering this will keep you from becoming alarmed when you gain back a bunch of weight the day after you start eating normally again.
  2. Improved Metabolic Health: Fasting can improve insulin sensitivity and other markers of metabolic health, reducing the risk of type 2 diabetes and cardiovascular diseases.8Mattson, M. P., Longo, V. D., & Harvie, M. (2017). Impact of intermittent fasting on health and disease processes. Ageing Research Reviews, 39, 46-58.
  3. Mental Clarity: Many fasters report improved focus and mental clarity, although scientific evidence is limited in this area. The brain-boosting effects are often attributed to increased ketone production.9Newburg, D. S., & Alverdy, J. C. (1994). Metabolic responses to starvation and injury. Nutrition, 10(1), 69-71.
  4. Longevity: Some animal studies suggest that fasting could extend lifespan by triggering cellular repair processes, although more research is needed in humans.10Fontana, L., & Partridge, L. (2015). Promoting health and longevity through diet: from model organisms to humans. Cell, 161(1), 106-118.

While these benefits are promising, they’re not universal, and individual experiences may vary. It’s also crucial to consult a healthcare provider before beginning any fasting regimen, especially for extended periods.

Water Fasting Drawbacks and Risks

Water fasting may offer intriguing benefits, but it’s not a one-size-fits-all solution. Here are some of the drawbacks and risks to consider:

Nutrient Deficiencies

Extended fasting deprives the body of essential nutrients like vitamins and minerals. These nutrients are vital for various bodily functions, including immune response and metabolic processes. Prolonged nutrient deficiencies can lead to issues like weakened immunity, poor bone health, and even cognitive impairments.11Calton, J. B. (2010). Prevalence of micronutrient deficiency in popular diet plans. Journal of the International Society of Sports Nutrition, 7(1), 24.

Risk to Specific Populations

Certain individuals should steer clear of water fasting due to elevated health risks. Pregnant women, for instance, risk nutrient deficiencies that can affect fetal development. Likewise, children and individuals with pre-existing medical conditions like diabetes or heart diseases could experience exacerbated symptoms or complications during a fast.12Anton, S. D., Moehl, K., Donahoo, W. T., Marosi, K., Lee, S. A., Mainous, A. G., … & Mattson, M. P. (2018). Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting. Obesity, 26(2), 254-268.

Muscle Loss

Although fat is the primary source of energy during fasting, extended periods can trigger muscle catabolism. Loss of muscle mass not only reduces strength but also lowers metabolic rate, making it easier to gain weight in the future.13Pasiakos, S. M., Cao, J. J., Margolis, L. M., Sauter, E. R., Whigham, L. D., McClung, J. P., … & Young, A. J. (2013). Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial. The FASEB Journal, 27(9), 3837-3847.

Potential Rebound Effect

Water fasting can be a double-edged sword when it comes to weight management. While you might shed pounds during the fast, a return to poor eating habits can lead to rapid weight gain. This rebound effect can be demoralizing and counterproductive, negating the benefits achieved during the fast.14MacLean, P. S., Bergouignan, A., Cornier, M. A., & Jackman, M. R. (2011). Biology’s response to dieting: the impetus for weight regain. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 301(3), R581-R600.

Common Myths and Misconceptions

The world of water fasting is rife with myths and misconceptions. Let’s debunk some of the most common ones:

Myth 1: Water Fasting is an Easy Way to Lose Weight

While it’s true that water fasting often leads to rapid weight loss, the pounds shed are not always from fat. Initial weight loss often comes from water weight and muscle mass. Plus, without a sustainable eating plan post-fast, you’re likely to regain the weight you lost.15Purcell, K., Sumithran, P., Prendergast, L. A., Bouniu, C. J., Delbridge, E., & Proietto, J. (2014). The effect of rate of weight loss on long-term weight management: a randomised controlled trial. The Lancet Diabetes & Endocrinology, 2(12), 954-962.

Myth 2: Water Fasting is Suitable for Everyone

As we’ve discussed, water fasting is not advisable for everyone. Pregnant women, children, and individuals with certain health conditions should avoid this practice.

Myth 3: Water Fasting Will Cure Diseases

Some proponents claim that water fasting can cure a myriad of diseases, from diabetes to cancer. While fasting does have therapeutic potential, it’s far from a cure-all. Always consult medical professionals for disease treatment.16Longo, V. D., & Mattson, M. P. (2014). Fasting: molecular mechanisms and clinical applications. Cell Metabolism, 19(2), 181-192.

Myth 4: You Can Fast as Long as You Want

Extended fasting without medical supervision can be dangerous, leading to severe nutrient deficiencies and other health risks. Always consult a healthcare provider for any fast lasting more than 72 hours.17Anton, S. D., Moehl, K., Donahoo, W. T., Marosi, K., Lee, S. A., Mainous, A. G., … & Mattson, M. P. (2018). Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting. Obesity, 26(2), 254-268.

Myth 5: Fasting Equals Starvation

While fasting involves restricting calories, it differs from starvation, which is involuntary and can lead to severe health consequences. Fasting is a controlled and voluntary abstinence from food.18Keys, A., Brožek, J., Henschel, A., Mickelsen, O., & Taylor, H. L. (1950). The biology of human starvation (Vol. 2). University of Minnesota Press.

Alternatives to Water Fasting

Water fasting isn’t the only route to achieving your health and wellness goals. If you find the practice too extreme or if you’re in a risk group that should avoid it, there are other options:

Intermittent Fasting

Intermittent fasting (IF) involves cycling between periods of eating and fasting. Unlike water fasting, IF doesn’t require you to abstain from all calories for extended periods. Common types include the 16/8 method, where you fast for 16 hours and eat within an 8-hour window, and the 5:2 method, where you consume a reduced-calorie diet two days a week.19Varady, K. A., & Hellerstein, M. K. (2007). Alternate-day fasting and chronic disease prevention: a review of human and animal trials. The American Journal of Clinical Nutrition, 86(1), 7-13.

Modified Fasting

Also known as the Fasting Mimicking Diet, this approach allows for a restricted caloric intake while still achieving some of the benefits of full fasting, like autophagy. You consume around 40-50% of your regular caloric intake on fasting days.20Wei, M., Brandhorst, S., Shelehchi, M., Mirzaei, H., Cheng, C. W., Budniak, J., … & Longo, V. D. (2017). Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Science Translational Medicine, 9(377), eaai8700.

Both of these alternatives offer a more flexible approach to fasting and can be more sustainable for long-term health benefits.

Practical Guidelines

If you’re considering water fasting, it’s crucial to approach it responsibly. Here are some practical guidelines to help you undertake a safe and effective fasting experience:

Consult a Healthcare Provider

Always consult with a healthcare provider before embarking on any fasting regimen, especially extended fasting, or if you have existing medical conditions.

Start Slow

If you’re new to fasting, start with shorter durations and gradually work your way up. This allows your body to adapt and minimizes potential side effects.

Stay Hydrated, But Not Too Much

While it’s essential to stay hydrated during a water fast, be cautious not to overhydrate, as this can lead to hyponatremia, a condition where your blood sodium levels become dangerously low.

Monitor Your Body

Listen to your body during the fast. If you experience severe fatigue, dizziness, or other unusual symptoms, it’s crucial to stop fasting and seek medical advice.

Plan a Healthy Diet Post-Fast

After completing your fast, reintroduce food gradually. Opt for nutrient-dense and protein-rich foods that can help replenish lost vitamins and minerals.

Following these guidelines makes you more likely to have a positive and beneficial fasting experience.


Water fasting is a practice steeped in history and backed by some intriguing science. It offers potential benefits like weight loss, improved metabolic health, and even enhanced mental clarity. However, it’s not a magic bullet or a one-size-fits-all solution. The practice comes with its own set of risks and drawbacks, including nutrient deficiencies and the potential for muscle loss.

If you’re considering water fasting, it’s crucial to weigh the pros and cons carefully. Consult a healthcare provider, especially if you plan to fast for an extended period or have existing medical conditions. And remember, if water fasting isn’t right for you, there are other, more moderate fasting options available that can still offer health benefits.

Finally, you might wonder if I’d recommend a multiple-day water fast if you were my client. The answer is , “no.” One of my first rules for nutrition and exercise is “Don’t lose muscle.” Fasting for multiple days undoubtedly increases the risk of muscle loss, and you can very likely achieve the same health benefits through intermittent fasting or other methods, so I’d have a hard time recommending it for a client.