Water fasting, which involves consuming only water for a specific period, has gained popularity as a method for weight loss and potential health benefits. While some studies suggest positive outcomes, it's crucial to understand both the advantages and disadvantages before embarking on this practice. Water fasts typically last 24-72 hours. This approach can be traced back thousands of years, and it has recently become fashionable. People often try it because they want to improve their health and lose weight.
What is Water Fasting?
Water fasting is a type of fast during which you cannot consume anything besides water. Most water fasts last 24-72 hours. You should not follow a water fast for longer than this without medical supervision. Some other names for it are extended fasting and prolonged fasting.
People try water fasting for various reasons, including:
- Religious or spiritual reasons
- Weight loss
- "Detoxing"
- Perceived health benefits
- Preparing for a medical procedure
Potential Benefits of Water Fasting
While research is limited, some studies suggest that water fasting may offer several health benefits:
Autophagy Promotion
Autophagy is a process in which old parts of your cells are broken down and recycled. Several animal studies suggest that autophagy may help protect against diseases like cancer, Alzheimer’s, and heart disease. Animal studies also show that autophagy may help extend life span. For example, autophagy may prevent damaged parts of your cells from accumulating, which is a risk factor for many cancers. This may help prevent cancer cells from growing.Animal studies have consistently found that water fasting helps promote autophagy.
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Lower Blood Pressure
Research shows that longer, medically supervised water fasts may help people with high blood pressure lower their blood pressure. One study in 48 people with overweight or obesity found that water fasting for an average of 17 days under medical supervision led to reductions in systolic blood pressure. It was also associated with improvements in levels of LDL (bad) cholesterol and inflammation. Similarly, another review concluded that water fasting could significantly reduce blood pressure levels and body weight in people with high blood pressure.
Improved Insulin and Leptin Sensitivity
Insulin and leptin are important hormones that affect the body’s metabolism. Insulin helps the body store nutrients from the bloodstream, while leptin helps the body feel full. Research shows that water fasting could make your body more sensitive to leptin and insulin. Greater sensitivity makes these hormones more effective. For example, being more insulin sensitive means your body is more efficient at reducing its blood sugar levels. Meanwhile, being more leptin sensitive could help your body process hunger signals more efficiently, and in turn, lower the risk of obesity.
Reduced Risk of Chronic Diseases
There is some evidence that water fasting may lower the risk factors of chronic diseases like diabetes, cancer, and heart disease. In one 2013 study, 30 healthy adults followed a water fast for 24 hours. After the fast, they had significantly lower blood levels of triglycerides - a risk factor for heart disease. Some research also suggests that water fasting may protect the heart against damage from free radicals. Moreover, studies in animals and humans have found that water fasting may suppress genes that help cancer cells grow. It may also improve the effects of chemotherapy.
Risks and Downsides of Water Fasting
Despite the potential benefits, water fasting carries several risks and may not be suitable for everyone.
Loss of the Wrong Type of Weight
Unfortunately, a lot of the weight you lose in the beginning may come from water, carbs, and even a small amount of muscle mass. Weight loss is inevitable if you’re eating nothing, but we know that moving toward a healthier lifestyle often involves small, simple changes that are realistic and manageable. What’s more, the weight loss likely stems from the body releasing glycogen (energy) stores from the liver and muscles. These stores hold a lot of water. So, much of the weight lost during water fasting is simply water. Plus, some weight loss is likely from muscle, and we generally want to preserve muscle.
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Dehydration
Although it sounds strange, a water fast could make you dehydrated. This is because roughly 20-30% of your daily water intake comes from the foods you eat. If you’re drinking the same amount of water but not eating foods, you might not be getting enough water. Symptoms of dehydration include dizziness, nausea, headaches, constipation, low blood pressure, and low productivity. To avoid dehydration, you may need to drink more than usual.
Orthostatic Hypotension
Orthostatic hypotention is defined as a drop in blood pressure that happens when you suddenly stand up, and it can leave you dizzy, lightheaded, and at risk of fainting. If you experience orthostatic hypotension while fasting, you may need to avoid driving or operating heavy machinery. The dizziness and risk of fainting could lead to an accident.
Worsening of Medical Conditions
Although a water fast is relatively short, there are a few conditions that may be aggravated by water fasting. People with the following medical conditions should not water fast without first seeking advice from a healthcare professional:
- Gout: Water fasting may increase uric acid production, a risk factor for gout attacks.
- Eating disorders: There is evidence that fasting may encourage disordered eating behaviors for some people.
Other Side Effects
Strikingly, almost 50% of the participants dropped out of the study. This highlights the challenges of only consuming water for extended periods. Some of the reasons that the participants left the study included headaches, feeling unwell, acid reflux, fatigue, anxiety, cramping, panic attacks, vomiting, and heart palpitations. The researchers found that most adverse events were mild to moderate, and these included fatigue, nausea, difficulty sleeping, back pain, indigestion, and headaches. Water fasting carries risks, including side effects such as mood changes, migraine headaches, and disordered eating. It can make you feel physically and mentally drained, too.
Refeeding Syndrome
Even after you’ve finished an extended water fast, there’s another risk - refeeding syndrome. This is a potentially fatal complication that can develop when people reintroduce food too quickly after a prolonged fast. This can trigger severe shifts in levels of fluids and electrolytes. In the 2021 and 2022 water fasting studies we mentioned above, the scientists were careful to reintroduce foods in a safe, gradual way.
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How to Prepare and Perform a Water Fast
There are no scientific guidelines on how to start water fasting. However, several groups of people should not water fast without medical supervision. If you have never water fasted before, it’s a good idea to spend 3-4 days preparing your body for being without food. You can do this by eating smaller portions at each meal or by fasting for part of the day.
Water Fast (24-72 hours)
During a water fast, you are not allowed to eat or drink anything besides water. The water fast lasts for 24-72 hours. You should not water fast for longer than this without medical supervision because of health risks. Some people may feel weak or dizzy during a water fast and may want to avoid operating heavy machinery and driving to avoid causing an accident.
Post-Fast (1-3 days)
After the water fast, you should resist the urge to eat a big meal. This is because eating a large meal after a fast may cause uncomfortable symptoms. Instead, break your fast with a smoothie or smaller meals. You can start introducing larger meals throughout the day as you feel more comfortable. The post-fast phase is especially important after longer fasts. This is because you may be at risk of refeeding syndrome, a potentially fatal condition in which the body undergoes rapid changes in fluid and electrolyte levels. This phase normally lasts a day, but people who fast for 3 or more days may need up to 3 days before they feel comfortable eating larger meals.
Alternatives to Water Fasting
If you want to reap the benefits of fasting but also want to lose weight, intermittent fasting and alternate-day fasting are probably more effective approaches than water fasting for 24-72 hours. These fasts provide similar health benefits but can be followed for much longer periods, as they allow you to eat food, decreasing the risk of nutrient deficiencies.
Intermittent Fasting
Intermittent fasting is a safer alternative to water fasting. It involves focusing on when you eat rather than what you eat. Several studies have shown that intermittent fasting can lead to weight loss. It may also have helpful metabolic effects, like improving your blood sugar control and levels of blood fats. Although it’s still early days, emerging research suggests that intermittent fasting may positively affect brain health. It may, for example, improve mental health and memory. There are several types of intermittent fasting, and one is time-restricted eating (TRE). It involves eating within a set window of time, which may last for 4, 6, or 8 hours, for example. The rest of the day you fast. The good thing about TRE is that it’s flexible - you pick the time frame that suits you. And unlike water fasting, TRE allows you to meet your daily nutrient requirements.
48-Hour Fasting
A 48-hour fast is a form of intermittent fasting that involves taking a 2-day pause on eating while drinking only calorie-free fluids. It may help with weight loss and cell regeneration, but it also carries certain risks. A 48-hour fast is one of the longest fasting durations, with shorter fasting periods being more common. In theory, a 48-hour fast is simple - you merely give yourself a full, two-day break from eating. One common method is to stop after dinner on the first day and begin eating again at dinnertime on the third.
Contrary to popular belief, you can still drink zero-calorie fluids, such as water, black coffee, and tea, during the fasting period. It’s vital to drink plenty of fluids to prevent dehydration, which is one of the major potential complications of longer fasts. Afterward, it’s important to gradually reintroduce food. That way, you avoid overstimulating your gut, which may lead to bloating, nausea, and diarrhea. On non-fasting days, you would maintain your usual eating pattern, making sure to refrain from overindulging in higher-calorie foods. It’s most common to do a 48-hour fast 1-2 times per month as opposed to once or twice per week, as required by other fasting methods. Appropriately spacing out your 48-hour fasts may offer greater health benefits. As 48-hour fasting is not advisable for everyone, you should try shorter fasts, such as the 16:8 or alternate-day methods, before a 2-day session. This will help you understand how your body responds to a lack of food.
Potential Benefits of 48-Hour Fasting
- May slow cell aging: Cellular repair is your body’s natural way of replenishing its cells. It may help prevent disease and even delay tissue aging. Improved cellular repair and delayed tissue aging may help support overall longevity, according to some research.
- May reduce inflammation: Temporary inflammation is a healthy immune response, but chronic inflammation can have serious health consequences, such as cancer, heart disease, and rheumatoid arthritis.
- Improves insulin sensitivity and blood sugar levels: Insulin serves as the storage hormone for carbs, protein, and fats. Carbs and fats are your body’s preferred source of energy. During a fast of 24 or more hours, glycogen - the storage form of carbs - is depleted, and insulin levels are reduced. This allows your body to burn mostly fat for energy, making stored body fat more available for use. Research notes that various types of fasting, including 48-hour fasting, may decrease insulin levels. What’s more, they improve insulin sensitivity, which allows your body to transport blood sugar more efficiently.
- May aid in weight loss: Intermittent fasting may boost weight loss, though studies on 48-hour fasts specifically are lacking. However, in a 2019 study that looked at blood samples from four people after 58 hours of fasting, researchers found an increase of 44 metabolites linked to health benefits such as muscle maintenance and antioxidant activity. That said, since 48-hour fasts should only be done 1-2 times per month, they may be best for individuals who prefer to fast less frequently but still want to lose weight.
Downsides of 48-Hour Fasting
- Hunger and dizziness: The main drawback of 48-hour fasting is severe hunger, although many people claim that this feeling is temporary. In one study of 768 people fasting for at least 48 hours, 72% of participants experienced side effects, including hunger, fatigue, insomnia, and dizziness. Therefore, it’s important to work your way up to a longer fast, starting with shorter durations. Always proceed with caution while fasting.
- Exhaustion and sluggishness: While fasting, stored carbs drop after 24 hours, prompting your body to burn fat for energy. As such, you may feel sluggish, especially if this is your first time trying a longer fast.
- May interfere with social eating: Any fasting can interfere with social eating, such as going out for meals with friends or dining with your family on holidays.
Who Should Avoid Fasting?
While fasting may benefit your health in general, it is not for everyone. Those with certain medical conditions should consult their medical practitioner before fasting, while others should not fast at all.
- people with type 1 diabetes
- people with low blood pressure
- those who are underweight or have a history of eating disorders
- women who are pregnant, nursing, trying to conceive, or have a history of amenorrhea
- those taking certain medications, such as insulin, blood pressure, blood thinners, and nonsteroidal anti-inflammatory drugs (NSAIDS)
If you’re taking any medications, make sure to check with your healthcare practitioner before starting a fast.
Tips to Prevent Complications During Fasting
Several common fasting side effects can be prevented with proper strategies.
- Stay hydrated: Fasting for extended periods can lead to dehydration if you don’t drink enough fluids and consume electrolytes. Sodium, magnesium, potassium, and calcium are essential electrolytes that can be quickly depleted if you’re abstaining from food. Therefore, it’s best to supplement with these nutrients if you’re fasting for longer than 24 hours. Stay hydrated by drinking water with a pinch of salt or electrolyte tablets, which you can easily buy online. Flavored, non-calorie sparkling water can also be a great hydration option.
- Reduce hunger: Drink black coffee or green tea to help reduce hunger levels.
- Stay busy: Keep your mind busy to prevent obsession with hunger. Distractions may include taking a walk, watching a movie, reading a book, or listening to a podcast.