Is Water Fasting Safe?

With a large and ever-growing percentage of the population overweight, many people are looking for the best, easiest, fastest way to shed their unwanted pounds. Losing weight means eating less, and there are lots of weight-loss diets to choose from, but some are better than others.

Some are very labor-intensive and involve complicated menus, time-consuming meal prep, or a more expensive food bill. Others, like water fasting, are straightforward, cheap, as well as effective and can be beneficial for all body types. 

Fasting is nothing new, and people have been fasting for thousands of years. Fasting was initially used for spiritual reasons, and people also fasted as part of cleansing rituals. More recently, fasting has gained popularity as a quick and easy weight loss method.

Is Water Fasting Safe

Water fasting can help you lose weight without having to count calories or make special meals. It’s arguably the simplest diet to follow. But, is this food restriction method safe, and should you try it?

By the end of this article, you’ll have the answer to that question!

What is a water fast?

Water fasting involves consuming nothing but water for a predetermined time – usually between 24-72 hours. That means no fruit juices, coffee, soda, or tea; the only thing you can drink is water, and no food is allowed.

People do water fasts for a variety of reasons, including:

  • Spiritual or religious reasons, such as lent
  • Detoxing
  • Before a medical procedure
  • Detoxification
  • Weight loss

Irrespective of the reason, water fasting will almost always result in weight loss, even if it’s being done for an entirely unconnected purpose.

How to do a water fast

CalendarThe main appeal of water fasting is that it’s very straightforward to do. You don’t need any special supplements or to buy any exotic groceries. Instead, all you need to do is choose a start day and time, decide how long you will fast for, and then begin.

Ideally, you should prepare for your fast by gradually reducing the amount of food you’re eating to get used to eating less. That way, going without food will be less of a shock.

Then, when it’s time to start your fast, you simply stop eating and drinking anything that isn’t plain water. Continue for 24-72 hours. Water fasts beyond 72 hours are not recommended. Longer fasts should only be attempted under medical supervision.

You should drink 2-3 liters of water per day, although you can drink more than this if you wish. At the end of the fast, you should endeavor to eat small, light, healthy meals to avoid overloading your digestive system.

Big meals could lead to stomach upsets, and if you eat too much or very unhealthily, you could undo all of the benefits of your fast. Depending on the length of your fast, you may need 2-3 days of small, carefully prepared meals before you are ready to eat normally.

What can you eat?

Woman Drinking a Glass of WaterWhile some types of fast allow you to eat certain foods or consume calorie-free beverages such as unsweetened herbal teas or water with lemon juice, a water fast is precisely that – no food and no drinks other than water. There is no limit to how much water you can drink, but you should make sure you consume around 2-3 liters to avoid dehydration. Excess water will be excreted by your urinary system, so if you drink more water than usual, expect to pee more too.

However, you should not force-feed yourself with water, as too much could lead to hyponatremia. Hyponatremia is when sodium and other electrolyte minerals become severally diluted.

Also known as water intoxication and overhydration, this condition is very rare, but the effects are serious and potentially life-threatening. Avoid this problem by limiting your water intake to a sensible level.


Numerous studies suggest that water fasts, and fasting in general, can be good for your health. The potential benefits of water fasting include:

  Accelerated autophagy – this is the removal and replacement of old, dead, and damaged cells. Damaged cells are linked to various medical conditions, including cancer, Alzheimer’s disease, and heart disease. Autophagy may also increase life span, which is why fasting is popular with life extensionists.

Doctor Checking Pressure  Lower blood pressure – hypertension, the medical term for high blood pressure, increases your risk of heart disease and stroke.

Hypertension is known as the silent killer because it has no outward signs and can only be detected through blood pressure testing.

Fasting can help lower your blood pressure without the use of medications.

However, the blood pressure-lowering effect of water fasting is relatively short-lived; you’ll need to fast regularly to continue enjoying this benefit.

  Improved insulin sensitivity – a lot of people are insulin resistant. This means that, when they eat carbohydrates and sugars, their blood glucose levels rise and do not fall. This can increase fat storage and weight gain and may lead to type II diabetes.

Fasting increases insulin sensitivity, which means the carbs and sugar in your blood can move more easily into your liver and muscle cells. Stable, low blood glucose is an essential factor for weight loss, a stable mood and energy levels, and preventing many serious medical conditions.

Women Eating Meat and Salad  Improved leptin response – leptin is one of the hormones that tell your brain that you’ve eaten enough; it’s the satiety hormone.

But, if you are leptin resistant, your brain may not be getting the message that you’ve had enough to eat, so you end up eating more than you should.

Fasting can help increase leptin sensitivity, so you feel fuller sooner and are less likely to overeat.

  Weight loss – providing you don’t overeat before and after you water fast, you should lose weight. While it’s impossible to say precisely how much weight you’ll lose, it’s not unreasonable to expect about one pound per 24 hours.

Some of this weight will be water, but most of it should be fat. However, to keep this weight off, you must not eat more food than normal when you break your fast.

Health risks

Fasting has some proven benefits, but it’s not entirely risk-free. Consider the following before trying water fasting.

  Orthostatic hypotension – this is low blood pressure caused by not eating and only drinking water. Typically, sufferers feel weak and dizzy and are at risk of fainting. This could be very dangerous if you operate heavy machinery or if it happens while you are driving. If you experience orthostatic hypotension, water fasting may not be for you.

Woman Tiredhealth  Worsening of existing medical conditions – water fasting may make the symptoms of some chronic medical conditions worse. These include:

  • Gout
  • Diabetes
  • Eating disorders

You should also not water fast if you are pregnant or nursing. If you have any concerns about your medical suitability for water fasting, you should speak to your doctor before starting.

  Dehydration – ironically, a water-only fast can lead to dehydration. That’s because you typically get 20-30% of our water from the food you eat. If you feel dizzy, nauseous, have constipation, or suffer headaches, you may need to drink more water. However, don’t go overboard, as you could end up overhydrated, which is just as dangerous.

  Malnutrition – as crucial as water is for your health, it doesn’t contain any vitamins and only a few trace minerals. Prolonged water fast could lead to malnourishment. For this reason, you should eat nutritionally dense food before and after your fast, focusing on low-calorie, unprocessed vegetables, and fruits.

Is it the healthy choice for you?

WonderingFasting is a very natural human condition. It’s something many people do when they’re feeling ill or after a period of overeating, like the holidays.

A water fast is just a more structured, scheduled form of skipping a few meals because you don’t feel like eating.

Is it healthy and safe? The answer is probably yes.

While only probably? Because most of the studies that support fasting were conducted on animals and not humans. Fasting should help you lose weight and maybe good for your short- and long-term health, but there are no absolute guarantees. There are also a few risks associated with water fasting.

Ultimately, if you want to try water fasting, start with a short 18-24 hour fast, take a break for a week or two, and try again. Increase both the frequency and duration of your fasts to determine if it’s right for you.

If you experience any adverse side effects, maybe water fasting is not a healthy choice for you, even if other people can do it with no ill-effects.

Bottom Line

Water fasting is a popular and simple way to lose weight. After all, all you need to do is skip a few meals and drink more water. What could be easier? And with no special meals to cook or expensive groceries to buy, you’ll have more time on your hands and more money in your pocket too.

However, while water fasting can help you lose weight and maybe good for your health, it’ll only work if you avoid overeating before and after your fast. Even if you have fasted for 48-72 hours, overeating will undo all of your hard work; what a waste of time!

For water fasting to work, you need to eat healthily the rest of the time too. Also, you’ll need to fast regularly, such as one day a week or three days a month. The occasional short water fast won’t do much for you.

If complicated diets are getting you down, or you don’t have the time or money to follow a more exotic eating plan, water fasting can work. However, while water fasting is simple, it’s not easy, so be prepared to have your willpower tested if you decide to try this diet for yourself.

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Patrick Dale is an ex-British Royal Marine and owner and lecturer for a fitness qualifications company. In addition to training prospective personal trainers, Patrick has also authored three fitness and exercise books, dozens of e-books, thousands of articles, and several fitness videos.

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