Fact-checked by Dr. Anthony Gustin, DC, MS.
Written by Brenda Godinez
Intermittent fasting can improve your health and increase longevity.
While the most popular fasting method involves drinking massive amounts of water, there’s another way to do an intermittent fast…
Why dry? This type of fasting takes water out of the equation.
If the first question that pops into your head was “wouldn’t I get dehydrated?”, you’re in good company.
Most people brush off dry fasting as something dangerous that should never be attempted, and there’s a lot of misinformation out there that fuels this fear.
Dry fasting can be extremely beneficial to cell regeneration and repair.
And dry fasting can be done safely as long as you take all the steps necessary to do it right.
In this article you’ll learn everything about how dry fasting works, why it works, and if you should try it:
Dry fasting is a type of fast that doesn’t allow any water intake. The lack of water may help accelerate some of the protective effects you get on a regular water fast, like reduced inflammation and metabolic health.
However, it’s a more advanced fasting method that only people who have previous experience with normal fasts should attempt.
Dry fasting is lesser known than water fasting and often considered dangerous, but did you know that millions of people around the world actually do an dry fast for a month each year?
During Ramadan, the ninth month of the Islamic calendar, Muslims do a total fast in which they don’t consume water or food during daylight hours (12 hours on average). In some polar regions, it can be as long as 22 hours.[*]
Fasting is used by nearly all religions as a form of cleansing, penitence, self-discipline, or to feel closer to their deities. Fasting is practiced in:
- Judaism (during Yom Kippur)
- Christianity (during Lent and Advent)
- Mormonism (one Sunday of each month)
- Buddhism (to aid meditation)
- Jainism (to reach transcendence)
- Islam (during Ramadan).
The Islamic, Mormon, and Jewish fasts are the only ones that prohibit water, so they’re true dry fasts.
The benefits of fasting are backed by research.
Just like regular fasting, dry fasting can be intermittent or prolonged.
Intermittent Dry Fasting
You can do an intermittent dry fast by eating and drinking only for a small window of time each day and fasting the remaining hours. The distribution can be:
- 16/8 intermittent fasting: You’d eat in a window of 8 hours and fast for 16 hours. This is the most common type of intermittent fasting.
- 20/4 intermittent fasting: You’d eat in a window of 4 hours and fast for 20 hours. This is less common.
The dry fast done by Muslims during Ramadan is often called Ramadan Intermittent Fasting (RIF) because it mimics a traditional intermittent fasting. People consume one meal in the morning, abstain from food and water for 10-18 hours a day, and then eat dinner late at night. This refuels their body before the next day’s fast.
Intermittent dry fasting is the best approach because it lets you to reap the health benefits of the fast without endangering your health.
Prolonged Dry Fasting
A prolonged dry fast is when you go without food or water for over 24 hours. This is not advisable because the extended lack of water can harm your health. Water is vital for the function of all your organs, so a dry fast should be kept short.
The dry fast done by Mormons on Sundays and Jewish people on Yom Kippur are similar to a prolonged fast, but they still don’t go above 24-25 hours. This long period increases the chances of experiencing unpleasant side effects like headaches, such as the “Yom Kippur headache” common in Jewish women[*].
Some sources make a distinction between a “soft” and “absolute” dry fast. A soft dry fast is a common fast that allows external contact with water (like showering or swimming). The absolute dry fast is an extreme approach in which you can’t have any contact with water, even bathing. However, there are no science-based benefits to doing an “absolute” fast, so you can stick to the normal soft fast.
You may wonder if a dry fast has any serious advantages over a water fast that will make it worth your while.
Even though most of the research on fasting has been done on the water-based version, emerging research, as well as studies on religious dry fasts, show some serious benefits to forgoing water.
Water-based intermittent fasting has impressive health benefits, like fighting cancer cells, neuroprotection, improved insulin sensitivity, promoting a longer and healthier lifespan, reduction of fat tissue, cellular repair through autophagy, and sustained ketosis.
When you fast, you allow your body to regenerate, heal, and get rid of harmful agents more easily.
An intermittent dry fast can further intensify this cleansing process without dehydrating you.
Get this: Limited fluid intake pushes your body to burn more fat since fat can be used to produce metabolic water (water that your body makes internally).
In other words, fat is the most efficient source of internal water.
Since you won’t be hydrating your body with external liquids, metabolic water is of extreme importance and your body will strive to make it from fat at a higher rate than it would on a water fast.
This fat-burning effect can accelerate and support your state of ketosis.
Given that fat is necessary for a successful dry fast, it’s ideal if you do it while following the ketogenic diet.
High-fat meals in between the fast will help you breeze through it with minimal discomfort.
Dry fasting on the keto diet is easier because you’ll experience less hunger, less thirst, less discomfort, and your body can produce more metabolic water from fat.
One study compared the effects of eating a meal high in fat, protein, or carbs before a traditional 12-hour dry fast.
People who ate fat before fasting had the lowest amount of discomfort compared to people relying on carbs or protein, and they also experienced less hunger and thirst compared to the high-protein group.
People relying on the high-protein diet had the most discomfort and side effects (11 vs. 3 just after fatty meals).[*]
Eating fat before the fast also provided these perks:
- Post-fasting systolic and diastolic blood pressures decreased significantly.
- Post-fasting glucose also decreased.
Fasting while on the ketogenic can also improve brain function and energy, because the blood-brain barrier becomes more permeable to ketones during any type of fast[*].
Here’s how a combining the keto diet with a dry fast can protect your brain:
- The fast makes your brain more receptive to ketones through a permeable blood-brain barrier.
- Having fewer liquids in your system means more fat burning to create metabolic water.
- More fat burning means more ketones in your bloodstream.
- Having more ketones in your system means more energy available for your brain.
A third advantage of dry fasting on the ketogenic diet is that fat can help suppress your perceived need for water.
This even happens to people who aren’t fasting. The more someone eats fat, the less they tend to drink water, according to research. On the other hand, foods like fiber, caffeine, and alcohol trigger a higher water consumption[*][*].
Dry fasting can protect your brain, metabolism, and prevent disease through impressive anti-inflammatory effects. Here are the top benefits of fasting without water:
#1: Enhanced Cognitive Function And Protection
An intermittent dry fast can have these effects on your brain:
- Increased neuron protection against dysfunction and degeneration
- Increased creation of new neurons
- Increased brain plasticity
- Decreased neuronal excitotoxicity
One study found that a Ramadan dry fast increased the levels of a neurotrophin called BDNF (brain-derived neurotrophic factor)[*]. Neurotrophins are proteins that promote the survival and growth of neurons.
The roles of BDNF are maintaining memory and learning capacity, regulating neurogenesis and neuronal survival in the adult brain, and metabolic regulation. In fact, its one of the proteins responsible for the positive adaptations of the brain in situations when there’s little food available[*][*][*].
Even a short-term fast can improve brain function by killing harmful or unnecessary cells through autophagy[*].
Another way a dry fast protects the brain is through ketone production. Ketone bodies reduce two things in your brain: glutamate (an excitotoxin that can cause neuronal death if unregulated) and oxidative stress[*].
#2: High Anti-inflammatory Activity
When you’re dry fasting, your inflammation levels plummet.
- TNF-α: This molecule is able to induce fever, inflammation, and cell death. It can increase the chance of Alzheimer’s disease, cancer, psoriasis, and inflammatory bowel diseases when it’s not properly regulated.
- CRP: High levels of CRP are associated with an increased risk of diabetes, hypertension, and cardiovascular disease
- IL-1b: Important mediator of inflammation and is linked to heart failure.
- IL-6: This proinflammatory molecule can worsen autoimmune diseases and infections. It’s associated with a higher risk of diabetes, juvenile rheumatoid arthritis, and further malignant growths in people with breast cancer.
- CXC Chemokines: Molecules that cause inflammation when unregulated.
Intermittent dry fasting also reduces inflammation by decreasing the levels of leukocytes (immune cells), because leukocyte-derived inflammatory molecules contribute to inflammatory diseases[*].
By reducing inflammation, a dry fast can help prevent many degenerative diseases.
#3: Balanced Lipids
Dry fasting can positively affect levels of triglycerides, good cholesterol, bad cholesterol, and total cholesterol.
Several studies show that after dry fasting[*]:
- HDL (good) cholesterol levels increased in women.
- Total cholesterol and triglycerides decreased in men.
- LDL (bad) cholesterol decreased in both sexes.
Interestingly, the quality of the fats you eat before and after your fast can affect your lipid levels.
For instance, people dry fasting in Morocco had a significant reduction in total cholesterol and triglycerides even one month after the fast had ended. Meanwhile, people in Kuwait doing the same fast had no significant changes in cholesterol or triglycerides[*][*][*].
This difference may be explained by the different fats consumed in each country. The positive effect on Moroccans was associated with a higher consumption of monounsaturated and polyunsaturated fatty acids, while Kuwait is more focused on saturated fat[*].
If you eat different fats before doing a dry fast, you’re more likely to experience lipid control.
#4: Glycemic Control
A dry fast can also regulate blood sugar, another important metabolic marker. This is no surprise, considering that the protective effects of fasting are in part thanks to a 50% reduction in glucose and insulin-like growth factor 1 (IGF-I).[*]
#5: Diabetes Prevention
Thanks to its glycemic benefits, dry fasting may prevent the onset of diabetes.
In Mormon communities who dry fast for 24 hours, studies find a lower incidence of diabetes. From the study groups, 20% of non-fasters had diabetes while only 10% of fasters had developed diabetes[*].
Another study found that patients with type 2 diabetes who did an intermittent dry fast for 15–21 days had a significant reduction of hemoglobin A1c (HbA1c) levels, which is an indicator of the average blood sugar concentration[*].
#6: Lower Blood Pressure
Many studies find that people have a lower systolic blood pressure at the end of dry fasts,[*] and these effects may be greater on a keto diet.
One study found that blood pressure had decreased after people ate either carbs, protein, or fat before the fast, but only those who ate fat had a remarkable reduction[*].
#7: Prevention of Coronary Heart Disease
Dry fasting may lower the risk of coronary heart disease.
Studies done on people who dry fast for 24 hours find they have a lower prevalence of coronary heart disease compared to non-fasters, even after adjusting for other risk factors[*].
Seventh-day Adventists tend to live approximately 7 years longer than other white adults, and this may be connected to the heart-healthy benefits of dry fasting[*].
#8: Bone Health
A molecule called parathyroid hormone (PTH), which is vital for bone formation and integrity, is increased during dry fasting.
This spike in PTH leads to bone resorption, bone formation, and increased calcium levels during and after a dry fast[*].
Some people can use water-based intermittent fasting for weight loss, but with dry fasting the effects on weight loss are mixed.
Research finds that people tend to have a lower body weight, body mass, and body fat at the end of dry fasting, but these effects are modest and short-lived since people gain most of the weight back afterward[*][*][*][*].
One meta-analysis found that after Ramadan, people had lost 1.2 kg on average. Across 16 follow-up studies, the average re-gained weight in the 2 weeks after Ramadan was 0.72 kg[*].
Most of the weight loss observed during dry fasting is due to two things:
- Lost water weight: At least half of your total weight is water weight (59% for men and 50% for women). When you dry fast, you’re bound to see a decline in total weight because of the reduced water in your system. Water weight is quickly gained back once you break the fast, so it’s not a reliable form of weight loss.
- Calorie restriction: The calorie restriction in dry fasting also helps with short-term weight loss, however, if you go back to eating higher levels of calories when the fast is over, you’ll gain the weight back.
This is why dry fasting alone is not enough to lose weight and keep it off. However, if you combine it with the ketogenic diet you will experience sustained weight loss.
One of the biggest concerns about dry fasting is dehydration. You would think that restricting water for half a day can’t be good for you, right? But it’s not that simple.
Will I Get Dehydrated During a Dry Fast?
Dehydration is a real threat if you don’t eat a healthy diet before and after the fast, but it can be avoided if you practice the right habits.
Researchers studied people who fasted during Ramadan (a month-long intermittent dry fast) to measure the effects of dehydration on their metabolisms. Surprisingly, dehydration was either mild or non-existent.
In one study, the concentration of urine samples collected in the afternoon was very high, which meant the body was effectively conserving water both by urinary concentration and lower urine quantity[*].
Perhaps the most fascinating findings came from Malaysian Muslims. Researchers found that total body water content was conserved during the fast despite the water restriction. Their bodies compensated the lack of water by minimizing water losses, which created internal balance[*].
The result is that total body water content remained roughly the same before, during, and after the dry fast:
These findings suggests that in a short dry fasting period, your body will work to balance its water content levels so you won’t experience dehydration side effects.
One of the possible side effects of dehydration is kidney stones, but studies find dry fasting isn’t a risk factor for stones because the concentration of crystal-forming substances in urine actually decrease[*].
Your dehydration risk might be even lower if you follow a high-fat diet, because according to Nature,“fat reserves and fatty foods are believed to be particularly valuable as a protection against desiccation”[*].
Wondering how your body can regulate itself when there’s no water? It’s explained in part by these five mechanisms:
#1: Water Turnover Rate
Your water turnover rate is the pace at which lost water (sweating or peeing) is replaced with new water (from drinks and foods).
In a dry fast, the water turnover rate is slowed down because there’s no incoming water except for metabolic water. This makes your body compensate by cutting off water losses (eg. less peeing), which maintains your body water at acceptable levels.
The general rule is that when water turnover rate is altered, total body water content is usually conserved[*].
#2: Secretion of The Antidiuretic Hormone (ADH)
When water is limited, your blood can start to get more concentrated. In the long-term, this makes your blood sticky and less able to circulate in your body properly.
Your body can prevent that in the short-term thanks to ADH.
During dry fasting, the lack of water in the blood triggers the secretion of ADH, which is in charge of reabsorbing water.
ADH travels to the kidneys and redirects water back into the blood, so your blood stays diluted and your urine is concentrated instead. The other way around (concentrated blood and diluted urine) can cause serious damage[*].
That’s why a high concentration of urine during a fast is a good sign of internal hydration.
#3: Turning Fat Into Water
As mentioned before, your body can use nutrients, but especially fat, to make metabolic water.
For every 100g of fat you have in store, your body can make 107g of water. On average, someone who uses up 2500 calories/day will make around 250mL of water per day[*].
This amount is not enough to cover your daily water needs, but it’s enough to cover the water you lose through respiration[*].
If you eat a high-fat diet, you’ll be able to burn more and produce more water. Evidence suggests that athletes gain more metabolic water through the oxidation of fat.[*]
#4: The Water Levels That Cause Dehydration Can Vary
Short-term water restriction is not likely to dehydrate you. According to the National Academies of Science, Engineering, and Medicine (NASEM), the slight drop in hydration that happens when you restrict fluids for a few hours is compensated by the day-to-day fluid intake (driven by thirst and consumption of meals).[*]
This is what happens in an intermittent dry fast.
You also might not need as much water as you think. The average recommended daily water intake is 2.7L for women and 3.7L for men, however, the National Academies explain that “as with AIs [adequate intakes] for other nutrients, for a healthy person, daily consumption below the AI may not confer additional risk because a wide range of intakes is compatible with normal hydration.”[*]
#5: Increased Water Intake After The Fast
One of the behavioral reasons people don’t dehydrate during a dry fast is they consume enough liquids before and after. Apparently, dry fasters compensated for daytime water restriction by drinking more during the night, which prevented them from becoming chronically dehydrated[*].
When you fast, your body will go through two stages of fuel burning:
Stage #1: Burning Glycogen (If You’re Not Fat-Adapted)
When there’s no food or water, your body will try to burn stored glycogen if you’re not fat-adapted. This burning mode can last 2-3 days, so this would be the only fuel in an intermittent dry fast.
Burning glycogen instead of fat will make your body produce less metabolic water and might cause more discomfort.
Stage #2: Burning Fat
You can take a shortcut and start burning fat from day one by adopting a ketogenic diet.
Using fat from the start will help you stay hydrated, lower thirst, prevent discomfort, and enter ketosis much faster.
Now that you know how dry fasting works, here’s how to do it in a safe way:
Dry fasting can improve many metabolic markers and protect against disease if you do it under the right conditions. It can be potentially deadly if you don’t know how to approach it. Here’s how to make it work:
Who Should Dry Fast?
- Someone who has plenty of experience with water fasts and has had no side effects from them.
- Someone who is fat-adapted.
- People who aren’t prone to migraines or headaches.
- Someone who isn’t coffee or tea-dependent.
- People without any eye-related diseases.
Who Shouldn’t Dry Fast?
- People who have never tried water fasts before, or those who have only done juice fasts.
- People who are prone to headaches or migraines, because a dry fast can trigger them[*].
- People dependent on stimulants like coffee and tea, because the withdrawal during the fast can cause headaches and moodiness[*].
- People with dry eye syndrome, glaucoma, or cataracts. Dry fasting has been shown to exacerbate the symptoms in these conditions[*].
How Long Can I Dry Fast?
An intermittent dry fast of 16 hours per day is ideal.
Intermittent dry fasting has been the most researched, while there’s no evidence to guarantee the safety of dry fasts that last more than a day.
4 Steps To Dry Fasting Success
Here’s how to succeed at dry fasting:
Step #1: Become Fat Adapted
Teach your body to burn fat instead of glucose by eating a high fat, low carb diet. You can become fat adapted in around one week by following a standard ketogenic diet, in which you consume:
- 70-80% of calories from fats
- 20-25% of calories from protein
- 5-10% of calories from net carbs (total carbs- fiber)
Use the keto calculator to find your individual keto macros.
Step #2: Experiment With a Water-Only Fast
Test the waters, literally. See how your body responds to water-based intermittent fasting instead of going cold-turkey on a dry fast.
This step is the most crucial because it will tell you if your body is prepared to try a dry fast at all.
Do an intermittent fast for a week in which you only eat 8 hours a day and spend 16 hours without eating (but drinking plenty of water).
If you don’t experience any serious adverse effects like headaches or excessive weakness your body may be able to handle a dry fast.
Step #3: Prepare Your Body One Week In Advance
It’s advisable you quit caffeine or other stimulants one week before the dry fast to avoid withdrawal symptoms. You can also start to cut down on meals and daily calories to make the transition smoother.
Step #4: Stick to A 16-Hour Dry Fast
Now you can try going 16 hours without eating or drinking anything and rehydrating only in the 8-hour window. You can do this intermittent fast for as long as you want, although a few days is enough to notice any positive (or negative) effects.
Thanks to the previous steps, you shouldn’t feel too thirsty, moody, or uncomfortable during the dry fast.
Mistake #1: Bingeing After The Fast Is Over
Overeating after fasting can cause digestive problems like bloating and stomach aches as well as rapid weight gain, especially if you eat too many carbs.
Transition out of the fast by eating in moderation and drinking plenty of water to hydrate your body.
Mistake #2: Exercising Too Hard
Excessive sweating will increase water loss, messing with your body’s efforts to maintain water balance. This can dehydrate you and make you light-headed.
If possible, save your intense gym sessions for before or after the fast. You can also opt for light exercise instead.
Mistake #3: Ignoring Your Body
Ignoring your body’s signals is the worst mistake you can make on any fast.
Pay attention to how you’re feeling throughout the dry fast and don’t hesitate to break the fast if you feel something’s not right. You might need to shorten the length of your fast or adjust some other lifestyle factors like exercise or caffeine.
A dry fast can be safe if you follow the conditions above: keep it short, eat plenty of fats, rehydrate when you’re out of the fast, experiment with water fasts first, and pay attention to your body.
A dry fast can be extremely harmful if:
- You do it longer than a day. This can cause severe dehydration.
- You’re taking medications. It’s not advisable to fast while on medications unless you are supervised by a doctor.
- You try it without experimenting with other fasts first.
- You’re exposed to excessive heat or physical exertion.
- You’re pregnant. Pregnant women should only fast under doctor’s orders.
Some of the side effects of dry fasting reported on studies are:
- Low performance in sports during the evening
- Temporal disrupted sleep (because of the change in circadian rhythms)
Dry Fast Safely
Dry fasting can enhance ketosis, banish inflammation, and improve metabolic health, but it shouldn’t be done by beginners without fasting experience.
To avoid any negative impact on your health, take the necessary steps to prep your mind and body before attempting your first intermittent dry fast.