Dry fasting: research, risks, and benefits

When fasting, people try to avoid food or other sources of energy for an extended period of time—anywhere from hours to days (Patterson, 2017). Dry fasting kicks things up a notch. During a dry fast, you basically eat and drink nothing. Even water is off-limits (Papagiannopoulos-Vatopaidinos, 2020).

Many popular fasting diets—including intermittent fasting plans, which are a form of calorie restriction—do not involve dry fasting (Mattson, 2018). However, some forms of religious fasting, including the observance of Ramadan among Muslims, can involve daily periods of dry fasting (Fernando, 2019).

Some people believe that dry fasting may have wellness benefits over and above those associated with other forms of fasting. But the research on this type of fasting is limited. 

Dry fasting is going without all food and drink, including water, for an extended period of time. While the exact definitions of fasting can vary, some experts define a fast as any period of voluntary restriction that lasts 12 hours or longer (Papagiannopoulos-Vatopaidinos, 2020; Patterson, 2017). 

Nearly all the published research on dry fasting comes from studies of Ramadan. Ramadan is an annual religious observance for those of the Islamic faith. It lasts for approximately one month (Adawi, 2017).  

During Ramadan, people do not eat or drink water—or any other beverages—between sunrise and sunset. However, they eat and drink in between those daily fasting periods (Fernando, 2019). Depending on where a person lives, this Ramadan period of fasting could last up to 18 hours, although the average is 13 hours (Adawi, 2017). 

Ramadan fasting resembles a practice known as time-restricted feeding. This is a method of fasting where a person restricts all their daily energy intake to a “time window” of eight hours or less (Mattson, 2017).

According to the Ramadan research, dry fasting can help lower body weight, reduce body fat, and contribute to improvements in cholesterol, blood glucose, and blood lipids that have a link to heart disease (Ismail, 2019). These weight-loss and body-composition benefits may be greater among people with overweight or obesity. Following the month of Ramadan, these improvements tend to fade (Fernando, 2019). 

Meanwhile, research on time-restricted eating has turned up similar health benefits. It’s not clear from all this work whether cutting off your water intake, on top of going without food and caloric beverages, leads to greater weight loss or health benefits (Ismail, 2019). 

Benefits of longer dry-fasting periods

When it comes to more extended dry-fasting periods, the published research is very thin. In one of the very few recent studies, 10 healthy men and women—some of whom had elevated BMIs—underwent a five-day dry fast, during which they were under medical supervision (Papagiannopoulos-Vatopaidinos, 2020).

The people in the study lost an average of 15 pounds, although a significant portion of that lost weight was, not surprisingly, water weight. The study authors note some big shifts in hormones, blood sugar levels, and blood pressure among the people in the study—shifts that they claim could lead to temporary health benefits, such as improved liver functioning. 

But that study also turned up risks (more on those in a minute) and found that most of the health changes edged back toward baseline following the period of dry fasting. The study didn’t explore many of the longer-term benefits of fasting, such as a lower risk for chronic diseases or improved lifespan (Papagiannopoulos-Vatopaidinos, 2020). 

To sum up, short periods of dry fasting may promote weight loss and other health benefits. But it’s not clear the “dry” component of this fasting method is necessary. Also, when it comes to longer periods of dry fasting, there’s very little published research.

Your body needs water. Going without water can cause dehydration, which comes with health risks. 

People who dry fast for more than a day report several symptoms and side effects related to poor hydration. These include fatigue and headaches, and to a lesser extent, muscle pain and nausea (Papagiannopoulos-Vatopaidinos, 2020). Likewise, research on dehydration—even mild dehydration—reveals many of these same symptoms. Dehydration can also lead to poor concentration and may also lead to poor cognitive functioning (Maughan, 2012). 

Meanwhile, research related to Ramadan has found that people certainly feel dehydrated. But because the waterless periods are limited to hours, not days, the practice seems to be generally safe for healthy people (Ismail, 2019). 

Severe dehydration, also known as hypohydration, can cause more serious effects. It can contribute to life-threatening electrolyte imbalances, as well as changes in brain structure and function (Sawka, 2015). It can raise your risk for kidney stones and urinary tract infections. And, as you probably know, going without water can be deadly (Maughan, 2012). 

Again, due to a lack of research, it’s difficult to say what longer-term health risks or problems may have a link to dry fasting.

Generally, fasting means that you’re choosing to restrict your food or calorie intake for a longer-than-usual period of time (Sen, 2018). Some fasting methods permit small amounts of calorie-containing foods, while others allow tea and other non-caloric drinks (Patterson, 2017). 

During water fasting, also known as water-only fasting, you eat nothing and drink only water (Ogłodek, 2019). Dry fasting is basically water fasting—minus the water (Papagiannopoulos-Vatopaidinos, 2020).

At this point, it’s hard to know the health benefits or risks of dry fasting. On the other hand, dehydration can cause some health problems—both mild and serious. If you’re considering dry fasting, it may be a good idea to talk with a dietitian or other medical provider first. 

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Current version

October 17, 2021

Written by

Health Guide Team

Fact checked by

Felix Gussone, MD

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About the medical reviewer

Felix Gussone, MD, Ro

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.