Water Fasting for Weight Loss Summary

  • Water fasting for weight loss can result in health benefits, but the metabolic benefits, such as lower blood pressure and improved cholesterol, however, these effects disappear soon after the fast ends.
  • Participants in these water fast diets lost about two-thirds of their muscle weight and one-third of their body fat. This contrasts with what happens during weight loss with high protein and resistance exercise, where more fat is lost than muscle.
  • Water fasting has been gaining popularity in recent years, with many people turning to it as a means of weight loss. However, the benefits of water fasting go beyond shedding those extra pounds.

Understanding Water Fasting

Water fasting diets, a practice involving temporarily abstaining from all food and only consuming water, has gained popularity in recent years, with many people turning to it as a means of water fasting for weight loss. The practice of willingly refraining from consuming solid foods and certain liquids, whether for therapeutic, spiritual, or political motives, has been ingrained in human societies for centuries.  Moreover, water fasting is advocated to heal and repair cells by giving the body a break from digestion.

The initial recorded instance of therapeutic fasting dates back to the 5th century BCE, attributed to the renowned Greek physician Hippocrates, who recommended avoiding food and drink for conditions he believed stemmed from excessive consumption. Nevertheless, there is limited research on water fasting; several studies have explored its effects on various aspects of health. (Longo & Mattson, 2014; Nencioni et al., 2018)

The allure of shedding pounds and rebooting the body has drawn many to explore its benefits. Furthermore, a recent study led by Krista Varady from the University of Illinois Chicago delves deeper into the actual impacts of water fasting for weight loss, revealing that its metabolic benefits may be more fleeting than previously thought.(Ezpeleta et al., 2023) There are various methods of water fasting, including intermittent fasting and extended fasting. It is important to consult with a healthcare provider before attempting water fast to ensure it is safe for you.

The Health Benefits of Water Fasting

The most common form of fasting is Ramadan intermittent fasting. Ramadan intermittent fasting is a type of intermittent fasting practiced by Muslims during the Islamic month of Ramadan. During Ramadan, Muslims abstain from eating and drinking from dawn to dusk. Ramadan fasting results in improvements in cardiometabolic risk factors. (Ajabnoor et al., 2017)

Additionally, water fasting benefits may be because even brief periods of fasting (e.g., overnight) reduce glucose levels sufficiently to increase the production of ketone bodies. (Anton et al., 2018) Ketone bodies are purported to regulate processes, resulting in mitochondrial benefits and improved cellular health.(Miller et al., 2018)

  • A 2019 study found that water fasting between 4 to 21 days can improve health and well-being. The study found that fasting can help reduce body weight, improve metabolic health, and reduce the risk of chronic diseases such as diabetes, heart disease, and cancer. Additionally, fasting may positively affect mood, cognitive function, and overall quality of life. (Wilhelmi de Toledo et al., 2019) Similarly, fasting can increase brain availability of serotonin, endogenous opioids, and endocannabinoids, which may enhance mood (Michalsen, 2010). Fasting may also be beneficial for chronic pain management.
  • A 2022 study recruited 48 overweight and obese participants who voluntarily underwent medically supervised water-only fasting for various medical reasons. The water fast last >10 days. The benefits of the water fast were weight loss, improved sensitivity, reduced blood pressure, decreased visceral fat, and enhanced cardiovascular benefits. (Scharf et al., 2022)

The Zero Calorie Diet

water fasting benefits water fasting for weight loss does water fasting shrink your stomach water fasting diet water fastingAdditionally, long periods of water fasting for weight loss, known as the “zero calorie diet,” were used to treat morbid obesity and associated diseases in the 1960s. (Runcie & Hilditch, 1974) Amazing, these medically supervised fasting periods could last up to 249 days or more. (Thomson et al., 1966) The protocol involved daily clinical monitoring, 2–3 L of water per day and 250 kcal of food intake, and a multi-disciplinary program including health education and physical activity.

Understanding Water Fasting: A Brief Overview

Several studies have examined water fasting for weight loss under medical supervision. One study found that a five-day water-only fast decreased metabolic syndrome risk factors and increased anti-aging biomarkers in normal-weight individuals. (Dourado et al., 2023) Another study reported that medically supervised water-only fasting can be a safe and effective means of normalizing blood pressure and may assist in motivating health-promoting diet and lifestyle changes. (Dourado et al., 2023)

What Happens When You Stop Fasting

A recent review paper examined the impacts of water fasting for weight loss, but more importantly, what happens when you stop fasting. The study was a literature review of eight studies on water fasting or Buchinger fasting, a medically supervised fast popular in Europe. The team reviewed the cumulative results of these papers to understand the impact of fasts on weight loss and other metabolic factors.


  • People who used water fasting diets for five days lost about 4% to 6% of their weight.
  • Those who fasted for seven to 10 days lost about 2% to 10%.
  • Those who fasted for 15 to 20 days lost 7% to 10%.
  • Only a few studies tracked whether participants regained the lost weight, but in one study, participants gained back all they had lost in a five-day water fast within three months.
  • Metabolic benefits like improvements to blood pressure, cholesterol, and blood sugar levels were short-lived, returning to baseline levels quickly after participants started eating again.
  • Participants in these prolonged fasts lost about two-thirds of their muscle weight and one-third of their body fat.
  • No serious adverse effects were reported, but common side effects included headaches, insomnia, and hunger. Participants lost more lean mass than fat mass during these prolonged fasts.

Is Water Fasting Safe?

water fasting benefits water fasting for weight loss does water fasting shrink your stomach water fasting diet water fastingHowever, it is essential to note that water fasting also carries risks and may not be suitable for everyone. Although rare, adverse events have been reported during medically supervised water-only fasting (Finnell et al., 2018). Fasting can also lead to dehydration and electrolyte imbalances if not correctly monitored (Toledo et al., 2019). Additionally, fasting may not be appropriate for individuals with certain medical conditions or those who are pregnant or breastfeeding (Azizi, 2010).

In conclusion, water fasting has been associated with various health benefits, including improvements in metabolic health, blood pressure, and weight loss. However, the new study shows that these beneficial effects may be temporary, and loss of muscle mass is a significant concern. Therefore, It is essential to consult with a healthcare professional before embarking on a water fasting regimen to ensure safety and effectiveness.


Ajabnoor, G. M., Bahijri, S., Shaik, N. A., Borai, A., Alamoudi, A. A., Al-Aama, J. Y., & Chrousos, G. P. (2017). Ramadan fasting in Saudi Arabia is associated with altered expression of CLOCK, DUSP, and IL-1alpha genes, as well as changes in cardiometabolic risk factors. PLoS One, 12(4), e0174342. https://doi.org/10.1371/journal.pone.0174342

Anton, S. D., Moehl, K., Donahoo, W. T., Marosi, K., Lee, S. A., Mainous Iii, A. G., Leeuwenburgh, C., & Mattson, M. P. (2018). Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity, 26(2), 254-268. https://doi.org/https://doi.org/10.1002/oby.22065

Dourado, M. A. A., Vieira, D. C. L., Boullosa, D., & Bottaro, M. (2023). Different time course recovery of muscle edema within the quadriceps femoris and functional performance after single- vs multi-joint exercises. Biol Sport, 40(3), 767-774. https://doi.org/10.5114/biolsport.2023.119984

Ezpeleta, M., Cienfuegos, S., Lin, S., Pavlou, V., Gabel, K., & Varady, K. A. (2023). Efficacy and safety of prolonged water fasting: a narrative review of human trials. Nutrition Reviews. https://doi.org/10.1093/nutrit/nuad081


Longo, Valter D., & Mattson, Mark P. (2014). Fasting: Molecular Mechanisms and Clinical Applications. Cell Metabolism, 19(2), 181-192. https://doi.org/10.1016/j.cmet.2013.12.008

Miller, V. J., Villamena, F. A., & Volek, J. S. (2018). Nutritional Ketosis and Mitohormesis: Potential Implications for Mitochondrial Function and Human Health. Journal of Nutrition and Metabolism, 2018, 5157645. https://doi.org/10.1155/2018/5157645

Nencioni, A., Caffa, I., Cortellino, S., & Longo, V. D. (2018). Fasting and Cancer: Molecular Mechanisms and Clinical Application. Nature Reviews Cancer. https://doi.org/10.1038/s41568-018-0061-0

Runcie, J., & Hilditch, T. E. (1974). Energy provision, tissue utilization, and weight loss in prolonged starvation. Br Med J, 2(5915), 352-356. https://doi.org/10.1136/bmj.2.5915.352

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). https://doi.org/10.3390/nu14061183

Thomson, T. J., Runcie, J., & Miller, V. (1966). Treatment of obesity by total fasting for up to 249 days. Lancet, 2(7471), 992-996. https://doi.org/10.1016/s0140-6736(66)92925-4

Wilhelmi de Toledo, F., Grundler, F., Bergouignan, A., Drinda, S., & Michalsen, A. (2019). Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects. PLoS One, 14(1), e0209353. https://doi.org/10.1371/journal.pone.0209353

Is water fasting a safe and healthy way to lose weight?

Water fasting for weight loss is not recommended as a safe and healthy way to lose weight. It can lead to dehydration, nutrient deficiencies, muscle loss, and a slowed metabolism. It is important to consult with a healthcare professional before attempting any extreme diet or fasting regimen.

Additional Information

Water fasting is a specific fasting method that involves completely stopping food intake and relying solely on water for an extended duration. This fasting approach has gained recognition for its potential health advantages and is commonly pursued for weight loss and spiritual purposes. However, while it appears to offer metabolic benefits like lowering high cholesterol and high blood pressure, these advantages seem to be temporary and fade away shortly after returning to a healthy eating regimen.

Water Fasting Benefits

Under medical supervision, this practice can improve insulin sensitivity and potentially reduce inflammation and oxidative stress in the body, promoting autophagy, a process crucial for cellular health and longevity. However, without proper supervision, it may pose several health risks, including hypotension, orthostatic hypotension, hyponatremia, and other potentially fatal conditions, especially when extended for a prolonged period of time.

Consequences of a Water Fasting Diets

Studies have shown that participants engaging in a short-term water fasting diet experienced weight loss but also faced risks such as dizziness, nausea, fainting, and nutrient deficiencies, emphasizing the importance of supervision during such practices. It is crucial to monitor kidney function, serum levels, and uric acid to prevent any adverse effects on the body’s immune system and overall health condition.

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