Water fasting for weight loss: does it work?


(1) Video lecture

(2) Article

  • How much weight loss can you expect from a water fast?
  • Diet after your water fast sustains the weight loss
  • Plan ahead
  • Exercise after your water fast burns extra calories
  • Fasting for weight loss and facing food addictions
  • Obesity = Unhealthy diet = Food additions
  • Facing food addictions with an eating disorder
  • Final thoughts

Video lecture (12:15)

Many people consider using a water fast for weight loss. Unfortunately this often ends in failure, and sometimes even leads to weight gain afterwards. This video and newly extended article takes a look at the key issues you should think about before beginning such a fast. Understanding the potential pitfalls and limitations of water fasting can help you to make your own weight loss program a success!

How much weight loss can you expect from a water fast?

A lot of people have unrealistic expectations about how much weight they can actually lose through a water fast. Burning fat means losing weight, so theoretically it should be possible to lose hundreds and hundreds of pounds, simply by continuing to fast.

Things aren’t quite this simple, though.

The actual amount of weight loss during a water fast varies considerably from person to person. Nevertheless, it would be fair to say that on average most people lose about 1 lb. (0.5 kg.) per day. So for a 10-day fast, you can expect to lose approximately 10 lbs (5 kgs). On top of this, it’s normal to drop an additional 2-4 lbs (1-2 kgs) in the first day or two, as food remaining in the gut empties out. (Of course, these additional pounds will be quickly regained once you’re eating again.)

After the first 10 days or so of water fasting, the amount of weight loss per day decreases. As your body’s ketosis becomes increasingly efficient, you simply don’t need to burn as much fat in order to derive the same quantity of energy. Sooner or later, you can expect a weight loss closer to about 0.5 lbs (0.25 kgs) per day. In other words, it becomes a law of diminishing returns. You have to put in more time fasting in order to experience the same amount of weight loss. So instead of needing approximately 20 days to lose 20 pounds (10 kgs), most people need 25-30 days. To lose 30 pounds (15 kgs), usually 40+ days is necessary.

If you’re truly determined to use a water fast to lose hundreds of pounds, it’s going to take a very long time.

To be brutally honest, most people don’t have the willpower to fast for several months – even if this is theoretically possible. However, even with the necessary motivation, it’s probably not a good idea. Fasts much longer than about 40 days run an increasing risk of incurring serious problems. Most commonly, electrolytes can slip out of balance: an issue which usually reveals itself only subsequently, during the refeeding process. On the extremely rare occasion that someone has died from water fasting, it is usually cardiac arrest caused by electrolyte imbalance.

There are a few documented cases from the 1960s when this actually happened. These all involved research studies investigating the use of an extremely extended water fast in order to lose weight over several months. Fortunately, we understand more about the physiology of fasting today – but it’s precisely because we do understand the biochemistry better now that such long fasts are almost always avoided.

Diet after your water fast sustains the weight loss

I can’t stress enough how important it is to get your diet right after a water fast to lose weight. Quite simply, if it’s the fast which takes the pounds off, it’s your subsequent diet which keeps them off!

There are no two ways about it. In order to enjoy lasting weight loss, you’ll have to change your eating habits. It’s not rocket science. If it was your old eating habits which got you into trouble in the first place, then returning to them after your fast can only result in a slow but steady return to your old weight.

Before you begin your water fast, you need to ask yourself the question: ‘Am I truly ready to change my diet?’ If the answer isn’t an emphatic yes, your fast is likely doomed to failure.

Plan ahead

Before you begin your fast, it’s also important to know what your subsequent diet will be. There are so many possibilities: from vegan to paleo, and everything in between. So long as the number of calories going in doesn’t exceed the number of calories you expend, then there’s no metabolic reason you won’t succeed. However, equally important is to know that your diet is going to be psychologically sustainable and emotionally rewarding over the long term. Otherwise, you’ll just give it up and things will spiral out of control. So whatever diet you pick: don’t choose it during the fast, hoping blindly for the best. Instead, test it out for a while before you begin, so you already know that your body resonates with it!

There are two further reasons to make friends with your post-fast diet. First, once hunger has fully re-established itself after your fast, you may well want to eat more. Unless you already have a lot of fasting experience, it’s completely human to want to ‘compensate’ for the lack of food during the fast. So following a diet which provides a good sense of comfort makes it easier to stop eating as soon as your body is full.

Second, everything in the body runs more efficiently after a fast. This means that your metabolism actually requires fewer calories than before the fast in order to power you through the day. Yes, you’ll need to eat a little less than before. So it’s crucial to feel fully comforted by what you do eat.

Check out the webshop on waterfasting.org

The webshop offers downloadable fasting plans and guides to help make your water fast a success.

Exercise after your water fast burns extra calories

Almost as important as your diet is the addition of some kind of exercise program after your fast. (Note: this is not to be confused with exercise during the fast, which is generally something to be avoided. See my video/article: ‘Can I work out during a water fast?‘)

If keeping the pounds off after a fast boils down to finding a balance between calorie intake and output, then clearly exercise is the single most important means to increase calorie output. Aerobic, cardiovascular forms of exercise tend to burn the most calories, so activities like swimming, running or cycling (in this order) are the most efficient in controlling weight. If your fitness level precludes running, then even walking provides a good solution, so long as you keep your breathing and heart rate elevated for a sustained period. Work within your limits – but do work! And, as is also true for diet, choose a form of exercise that you enjoy.

A further benefit of a sustainable exercise program is that, over time, it raises your metabolic rate. Essentially, metabolic rate is the rate at which you burn calories, regardless of whether you’re moving or not. This means that even while you’re asleep you’re burning calories more quickly than if you don’t exercise. In addition to cardiovascular exercise, strength training also benefits your metabolic rate.

Fasting for weight loss and facing food addictions

Sustainable weight loss is achieved through three fundamental elements:

(1) the water fast itself,

(2) a healthy diet after the fast and

(3) regular exercise after the fast.

Impacting on the first two of these is the issue of food addictions.

There are both physical and psychological food addictions. On a physical level, certain foods like refined sugars and flavour enhancers initiate biochemical changes in the brain which ‘reward’ us for eating the given food, so that we want more. On an emotional level, food addictions come into play the moment we’re no longer eating purely to sustain our physical nutrition. We all suffer from them: eating for comfort, eating to relieve boredom, eating to soothe anxieties. (For more details, see my article: ‘Overcoming addictions through water fasting.’)

Obesity = Unhealthy diet = Food additions

People usually become overweight because they’re eating an unhealthy diet. Unhealthy diets are driven by food addictions. It’s that simple. This means that if you’re overweight and want to fast to lose the extra pounds, you’re going to have to face those addictions: both during the fast itself and afterwards, by eating a healthier diet.

Are you truly ready to face your addictions? I won’t lie to you. It won’t be easy.

Facing these addictions means experiencing withdrawal symptoms, whether physical (headaches, low energy etc.) or psychological (cravings). Truly freeing yourself from the psychological factors underlying such addictions also means opening up on a deeper level. If you allow your deeper self to speak to you, water fasting helps to bring forth and heal the emotional wounds which led to your addiction in the first place.

Are you ready to face these wounds – and the pain caused by them? If the answer is ‘no’, it’s going to be very difficult to successfully carry out your water fast and sustain weight loss afterwards.

Facing food addictions with an eating disorder

Fasting for weight loss causes even more problems for those with an eating disorder. Given that the degree of addiction and associated psychological complications is usually much more involved in such cases, water fasting can easily exacerbate the problem. I’m not suggesting that water fasting can’t help someone with an eating disorder lose weight, but it must be done with a high degree of caution (and preferably supervision).

There must be no illusions here. For anyone with an eating disorder, a fast for weight loss means a direct confrontation with the eating disorder itself.

Are you truly ready for this? If not, it’s all too easy to face the underlying issues and fail, slipping further into the cycle of addiction. So instead of losing weight and helping to heal the eating disorder, you actually end up deepening both problems.

Final thoughts

Most of this article has presented a cautionary tale of the pitfalls and potential dangers of trying to water fast in order to lose weight. Rightly so: too many fasts of this kind end in failure. However, this isn’t to say that it can’t be done. In order to put the odds in your favour, though, you do need to know where the problem areas are and how to plan for them – doing so well before the actual beginning of your water fast.

So be realistic. Don’t jump into this on the spur of the moment. And don’t allow any idealistic, well intentioned goals to overshadow your true capabilities. Instead, take your time, plan it out:

And make a success of it!

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