Can I work out and exercise during a water fast?


(1) Video lecture

(2) Article

  1. Confusion between juice and water fasts
  2. Facing addiction to exercise
  3. Slowing down to heal
  4. Fear of losing muscle mass while fasting – and why this is a misguided concern
  5. Water fasting and human growth hormone (HGH)
  6. What kind of exercise is okay during a water fast?
  7. What kind of exercise isn’t okay during a water fast?
  8. When is working out okay during and after a water fast?

Video lecture (13:55)

Whether or not it’s a good idea to work out during a water fast is a question which crops up surprisingly frequently on In general, most FAQs to do with water fasting usually lack a ‘one-size-fits-all’ answer, because it depends on the individual circumstances of the individual fast, along with the reasons that the individual person is fasting. In this case, though, the answer is clear-cut and applies to everyone: do not plan on working out or any serious exercise during a water fast!

I know this won’t be a popular answer, and many of my water fasting clients also resist the idea before they know any better. But there are several important reasons to rest while fasting. We’ll cover these below, in order of ascending importance, saving the most important – which is actually a question of preventing damage to your health – until last!

Confusion between juice and water fasts

Most people who approach water fasting do so after having done some juice fasting first. Juice fasting often permits a good degree of exercise because the calories they contain provide energy. Most of these calories also usually come in the form of simple sugars, which are easily burnt. In contrast, water fasting obviously provides no calories at all, and this changes everything (see below). In addition, water fasting induces higher levels of cleansing than juice fasting. This leaves less energy left over for other activities, such as working out and exercise.

Facing addiction to exercise

If you enjoy working out in everyday life, then it’s almost certainly going to be hard to shake the habit – even though a fast hardly counts as ‘everyday life’. I know. It took me years to learn to let go of the desire to exercise while fasting. Even though I did rest while fasting because I knew it was bad for me, something nevertheless continued to resist the idea of slowing down. Part of it is societal. Quite simply, the modern world glorifies busy-ness and work, work, work. But I also had to face the fact that I was addicted to the endorphins. It’s also true that most people who work out are equally addicted to endorphins.

Fasting is a time to face your addictions (more detailed information can be found in my article: ‘Overcoming addictions through water fasting’). Through fasting you learn how to be without the need for external distractions and frills. Allowing your hormones to reset without extra endorphins, caffeine, nicotine or any other drug, you learn that life is already good as it is.

Slowing down to heal

If you’re like most people in the modern world, you’re too busy for your own good, suffering from stress in everyday life. A limited amount of stress is actually good in many circumstances, but the problem is that most of us don’t get enough down time to balance this out. Fasting is a perfect opportunity for this!

More importantly, any energy spent on working out is going to take away from the energy available for healing. It’s that simple.

Fear of losing muscle mass while fasting – and why this is a misguided concern

Perhaps more than anything else, people feel compelled to work out during a water fast because they are afraid of losing muscle mass. Logically, this makes total sense. As the saying goes: use it or lose it! The problem is that working out during a water fast leads to a greater degree of muscle loss than not exercising at all. This is due to the metabolic changes which take place while fasting.

In everyday life, your body exists in a so-called anabolic state. Most people have heard of this word in relation to anabolic steroids: hormones which are designed to build muscle in order to enhance athletic performance. In general, anabolic simply refers to any state in which the body grows or builds itself up. In everyday life you eat, and the nutrients from food allow your body to build itself up.

While water fasting, though, your body exists in a so-called catabolic state. With no intake from food, your body changes priorities. Rather than building things up, it uses the available materials it already has to engage in cleansing and healing instead. Simply put, you can’t build up muscle when there’s no protein going in! Furthermore, working out while fasting actually reduces muscle mass. This is because exercise inherently causes a degree of micro muscle damage. It is precisely this damage which causes your body to build muscle when in an anabolic state. Your body detects the damage, and then builds additional new muscle in the area in order to prevent damage in the future. In a catabolic state, though, there is no protein to build new muscle. Instead, working out while fasting causes muscle damage which cannot be replaced with new, additional muscle. The damage is simply cleansed by the immune system, and you end up with less muscle than before.

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Water fasting and human growth hormone (HGH)

Fortunately, there’s no need to worry about muscle loss while water fasting. Fasting is one of the best ways to naturally promote the production of growth hormone. Elevated levels of HGH continue long enough after the fast to allow your body to easily make up for any loss of muscle during the fast. You don’t need to hysterically exercise after your fast – it will all return naturally. In fact, you can capitalise on the extra growth hormone in order to reach new levels of fitness and personal bests during the period after your fast (see below).

Similarly, there’s no need to start eating an extra high-protein diet after the fast in order to compensate for what you’ve lost. In fact, high-protein diets are the number one cause of problems during refeeding after fasts of up to about 10 days. When clients come to me with problems in refeeding, nine out of tens times it’s because they have reintroduced too much protein too soon after the end of their fast.

What kind of exercise is okay during a water fast?

Although hardcore workouts are downright damaging while water fasting, gentler forms of exercise can and do have a beneficial effect – so long as they don’t cause micro muscle damage in the process. For instance, gentle walking, stretching, yoga, as well as gentle cardiovascular exercise in general all help to promote detox. By burning more calories than usual, your body releases toxins stored in fat cells. The increased circulation of gentle exercise also helps to flush these and any other toxins out from the tissues, from where they can be cleansed from the body.

More generally, any exercise which feels good is probably good for you. While fasting, your body offers very clear signals about what kinds of exercise it is happy to do. The key is to listen and to respect this! Especially for those addicted to working out, though, it’s tempting to override these messages and force the kind of performance out of yourself which only causes damage. In everyday life you can get away with pushing through the pain. While water fasting you can’t!

What kind of exercise isn’t okay during a water fast?

It’s very simple. Any exercise which feels difficult, laboured, painful or unpleasant during a water fast is probably causing you damage. You never want to get to the point of sore muscles the next day, because in the catabolic state of fasting your body simply cannot repair and replace the damaged muscle cells.

Also, it’s important to avoid any activity which approaches the so-called anaerobic threshold: the point beyond which your circulation is unable to provide enough oxygen to power your muscles. (This basically means panting, a pounding heartbeat, and not being able to sustain the given activity for an extended period of time.) Although the ketosis of water fasting is able to provide enough energy for aerobic activity, anything approaching the anaerobic threshold requires your carbohydrate metabolism to kick in as well. Given that your glycogen stores are depleted during a water fast, anaerobic exercise quickly leads to accelerated muscle damage. While water fasting, you’ll also reach the anaerobic threshold much faster than in everyday life. Even if you’re just walking, ascending a hill can easily leave you out of breath. So slow down and feel into what the right, sustainable pace is for you!

Exercise of any kind is to be avoided on Day 2 of a water fast. At this point, your glycogen stores have already run out and ketosis is not yet fully engaged. This means that the main source of fuel are your muscles themselves, because the protein in muscle can be broken down into carbohydrates for energy. In fact, this is the primary reason why people often have sore muscles on Day 2 of a water fast – even without doing any exercise at all!

When is working out okay during and after a water fast?

Although working out is almost always something to be avoided during a fast, the one and only exception to this is on Day 1. At this point you still have glycogen reserves to provide carbohydrate based energy, and your body is still harvesting the nutrients from your last meal. This means that you haven’t fully entered a catabolic state yet (see above). Although it’s probably not a good idea to push yourself through an exceptionally hard work out, normal daily exercise on Day 1 is fine. In fact, burning more calories compared to resting helps you to consume your glycogen stores faster, which helps to accelerate the process of getting into ketosis. I often go for an easy, long run on Day 1, and it’s never a problem.

After a fast, it’s important to resist the temptation to start working out too soon. Remember: there’s no hurry to return to serious exercise due to the continuing elevated levels of growth hormone afterwards. Immediately after a fast the body’s priority is to work on your inner organs and body systems – and not the muscles! The liver, kidneys, lymphatic and immune systems all work overtime while water fasting. Once you’re taking nutrients on board during refeeding and you return to an anabolic state (see above), your body focusses first on rejuvenating and rebuilding them, and not muscles.

If you start working out too soon, you’ll only damage your muscles in the same way as during a fast. Also similar to during a fast, your body will continue to give you signals if exercise isn’t a good idea by making it feel difficult, laboured or unpleasant. In my experience, I find this period tends to last up to half the length of the fast, after the end of the fast itself. In other words, after a 3-day fast you’ll need to wait 1-2 days before working out, and after a 7-day fast you’ll need to wait 3-4 days.

After this point, the body turns from the core of the body to the periphery, and it quickly starts building back muscle through elevated levels of growth hormone. I usually return to my full pre-fast strength by the time the length of the fast has elapsed after the end of the fast itself (eg. 7 days after the end of a 7-day fast).

This isn’t the end of the story, though. Elevated levels of HGH continue significantly longer, allowing increased athletic performance beyond pre-fast levels. After a 7-day fast, for instance, I usually find that my performance (in terms of both strength and endurance) increases by about 5% for about a month afterwards.

Good things come to those who wait. So get the best of both worlds: slow down and relax while fasting, and then enjoy working out again afterwards!

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58 responses to “Can I work out and exercise during a water fast?”

  1. Thanks for this . Helped alleviate concerns I had about maintaining muscle mass / loss.

    1. Tallis Barker, D.Phil. Avatar
      Tallis Barker, D.Phil.

      Hi Hassan,
      Glad this video article helped!
      All the best,

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