A method restricting the intake of food, fasting has been around for thousands of years.

Water fasting, which is a type of fast restricting everything but water, has gained popularity in recent years as a quick way to achieve weight loss.

This type of fast has been shown to have health benefits. For instance, it may stimulate autophagy, which is a process that helps the body clean out damaged cells and regenerate newer, healthier cells, as well as lower the risk of some chronic diseases.

Although it might potentially offer health benefits, water fasting may also come with several health risks, making it not suitable for everyone. Human studies on water fasting are however very limited.

Here we give you an overview of water fasting, its benefits and risks, and how it works.

What is water fasting?

Water fasting is a popular type of fast that restricts everything but water.

Most water fasts would last for a day or two. Do not follow this type of fast longer than its recommended duration without medical supervision.

People usually try water fasting due to the following:

• for “detoxing”
• to lose weight
• for its health benefits
• to improve their health
• religious or spiritual reasons
• preparing for a medical procedure

Water fasting has been linked to some impressive health benefits, including a reduced risk of diabetes, heart disease, and certain cancers. It may also promote autophagy, which is a process that helps the body clean out damaged cells and regenerate newer, healthier cells.

Popular diets, such as the lemon detox cleanse, which only allows you to drink a mixture of water, lemon juice, cayenne pepper, and maple syrup for 7 days, are modeled after the water fast.

However, when followed for too long, water fasting may be potentially dangerous.

How to water fast?

Considering that water fasting can be potentially dangerous, several people, including older adults, children, pregnant women, and those who have medical conditions, should not water fast without medical supervision.

No scientific guidelines have been set on how to water fast.

However, if you haven’t fasted before, preparing your body without food for 3–4 days is a good idea. You can start by fasting for part of the day or by consuming smaller portions each meal.

Water fasting before and after

Water fast (24–72 hours)

During the water fast, you are not allowed to consume anything but water, and most people drink 2–3 liters of water per day.

You should not do the fast for longer than 24–72 hours without medical supervision as it can also be potentially dangerous.

During the fast, some people may feel weak or dizzy. That said, you may want to avoid driving or operating heavy machinery to avoid accidents.

Post-fast (1–3 days)

Eating a big meal right after the fast is a big no-no, as it may cause uncomfortable symptoms.

Before you start introducing larger meals to your stomach, slowly break your fast with smaller meals or with a smoothie for about 1–3 days.

This phase is particularly important for longer fasts; otherwise, you may be at risk of refeeding syndrome.

Potential water fasting benefits

Water fasting has been linked to a variety of health benefits in both human and animal studies.

It may help reduce blood pressure.

Longer, medically supervised water fasts have been found to help people with high blood pressure lower their blood pressure.

In fact, a study in 68 people with a borderline high blood pressure who tried medically supervised water fast for nearly 2 weeks found an 82% reduction of blood pressure to healthy levels. In addition, the average significant drop in blood pressure was 7 mmHg for diastolic (the lower value) and 20 mmHg for systolic (the upper value).

However, the link between short-term fasts and human blood pressure has not been investigated.

It can potentially promote autophagy.

As mentioned earlier, autophagy is a process that helps the body clean out damaged cells and regenerate newer, healthier cells.

This process has been found in several animal studies to help protect against diseases like heart disease, cancer, and Alzheimer’s.

For example, autophagy may help prevent the accumulation of damaged cells, which is a common risk factor in many cancers. Moreover, this process has also been shown in animal studies to help extend life span.

Human studies on water fasting, disease prevention, and autophagy are however very limited, necessitating further human studies.

It may improve leptin and insulin sensitivity.

Hormones leptin and insulin are important in the body’s metabolism. Leptin helps you feel full, while insulin helps your body store nutrients from the bloodstream.

Water fasting has been found to potentially improve leptin and insulin sensitivity, which may make these hormones become more effective.

For example, greater leptin sensitivity may help your body process hunger signals more efficiently, thereby lowering your risk of obesity; meanwhile, greater insulin sensitivity may help your body become more efficient at reducing blood sugar levels.

It may lower certain chronic disease risks.

Fasting has been shown to reduce the risk of chronic diseases like heart disease, cancer, and diabetes.

A study in 30 healthy adults who water fasted for 24 hours found a significant reduction in blood levels of triglycerides and cholesterol, which are risk factors of heart disease.

In addition, water fasting has also been found in animal research to suppress genes that help in cancer cell growth. What’s more, it may also improve chemotherapy effects.

Further human studies on the matter are however necessary before making recommendations.

Water fasting dangers

Not only does water fasting offer health benefits, it also comes with potential dangers.

You can potentially lose the wrong type of weight.

Restricting calories may cause you to lose weight quickly.

Water fasting for 24–72 hours has been found to cause up to 2-pound weight loss, which may come from carb, water, and even muscle mass.

You may experience orthostatic hypotension.

Defined as a drop in blood pressure when you suddenly stand up, orthostatic hypotension can leave you lightheaded, dizzy, and at risk of fainting. It’s common among people who are water fasting.

Orthostatic hypotension could lead to an accident, so you may need to avoid operating heavy machinery or driving while fasting.

It may worsen several health conditions.

Aside from children, older adults, and pregnant women, people with the following health conditions should not water fast without medical supervision.

Eating disorders. Fasting has been found to potentially encourage eating disorders like bulimia.

Diabetes. Fasting may potentially trigger the risk of adverse side effects in diabetes (both type 1 and type 2).

Gout. Water fasting may also increase the production of uric acid, which is a risk factor for gout attacks.

Water fasting for weight loss

Although it may help you lose weight, water fasting can definitely come with plenty of health risks.

If you want to lose weight by fasting, you can try other types of fasting, including alternate-day fasting and intermittent fasting. They provide similar health benefits and reduce the risk of nutrient deficiencies, as you are allowed to eat food. These are way more sustainable in the long term than the water fast.

Conclusion

Water fasting may offer some health benefits.

However, it is noteworthy that most of its health benefits have been observed in animal studies. Moreover, this type of fast also comes with several risks, especially if followed longer than 1–2 days.

Water fasting is absolutely not suitable for children, older adults, pregnant women, and those with medical conditions including gout and diabetes.

Intermittent fasting and alternate-day fasting are safer to follow than the water fast, as you are allowed to eat some food, making them more sustainable in the long term. They provide similar health benefits as well.