Is water fasting safe?


(1) Video lecture

(2) Article

  1. Fears about fasting
  2. Is water fasting safe?
  3. Why water fasting is safe?
  4. Fasting versus starving
  5. Discomfort versus danger
  6. Danger arises when brain overrides body
  7. People for whom fasting is dangerous
    • Cardiac issues
    • Type 1 diabetes
    • Toxic drugs and medications
    • Psychological imbalances
    • Rare metabolic disorders
    • Fasting with any medical issue
  8. Refeeding and eating
  9. Final thoughts

Video lecture (21:05)

Many people are convinced that water fasting must be dangerous. Unfortunately, this is mostly based on fear, misinformation, and only a minimal number of actual cases. This video and newly expanded article examines all the facts through a variety of different issues, also covering the exceptional circumstances in which water fasting really does become unsafe. Knowledge is power: so read on, gain the facts, and fast with confidence – not fear!

1, Fears about fasting

Let’s get straight to the heart of the matter. Most people are afraid (or at least a little anxious) about giving up food. Fair enough, if you stop eating for too long, starvation is the only possible outcome. So when we hear wildly dramatic statements like: ‘if you water fast, you’ll die’, a part of us resonates with the idea deep down inside.

In combination with this instinctive response, our more rational mind can also easily fall prey to fears about fasting. Over the last 100 years, modern Western medicine has disempowered our trust in ourselves and our bodies’ own natural wisdom to heal. Instead, pills and potions have become the name of the game, and today we entrust our wellbeing to medical doctors instead. With a training based almost entirely around pharmacology, it isn’t that surprising that even most well intentioned MD’s simply don’t get it. Fair enough, when your whole world revolves around putting medicines into the body, the idea of not putting in anything at all seems all the more contradictory, if not downright dangerous.

2. Is water fasting safe?

So can you die while water fasting? I won’t lie to you. The answer is yes – just like you can die getting up in the morning or crossing the road. All of life is a risk. Taking a full perspective on the issue, though, water fasting is totally safe for the vast, vast majority of people.

Don’t just believe me. Believe Google. I would suggest that anyone who has lingering doubts type the search terms “water fasting” and “death” into the world’s largest search engine, and see what comes up.

Essentially nothing.

Yes, a few isolated historical cases have been documented in which people died. Most of these, however, involved fasts lasting several months, and were conducted with disregard for the body’s warning signs (to be discussed later in this article, as well as in my video-article on fasting to lose weight).

Besides this, you’ll find only a lot of heated personal opinion as well as vague, unsubstantiated horror stories.

3. Why is water fasting safe?

It’s only been in the last hundred years or so that those of us living in the Western world have had unlimited access to food: every day of every month, year in, year out. Before that famine was an unavoidable fact of life – as it still remains across other regions of the Earth today.

On a physiological level, the initial stages of famine are identical to fasting.

Over the millennia humankind has proved itself remarkably resilient to famine, and each of us is designed to be able to last 6-9 weeks, if not more, without food. You might say that we are born to fast as much as we are to eat. Both are – or at least should be – totally natural to us.

It’s in our blood. We’ve been doing it for hundreds of thousands of years, and we’re still here to tell the tale!

To take another historical perspective, think of it like this: if fasting were somehow dangerous to us, evolution would have weeded out those of us incapable of fasting long, long ago.

4. Fasting versus starving

I’ve already mentioned the obvious fact that if you stop eating for too long, starvation is the only possible outcome. This really is the crux of the matter in terms of safety.

Fasting means that your metabolism is able to sustain homeostasis: a state of equilibrium maintained between the various elements of the body and among the various physiological processes which keep you alive. Yes, you’re burning fat, but all your other body systems are stable and therefore running safely.

Starvation begins once the body can no longer keep things in balance, and homeostasis is lost. As mentioned above, it usually takes at least 6-9 weeks of continuous fasting to reach this point. Usually, this is triggered by fat levels having dropped to approximately 2% of body weight, which causes the body to start cannabilising muscle tissue for fuel, as well as eventual damage to the inner organs. Another dangerous situation arises if electrolytes gradually shift out of balance, making homeostasis impossible to maintain. Again, this is highly unlikely to happen in under 6 weeks of fasting – especially if you began the fast as an otherwise healthy person. If you do reach the initial stages of starvation, though, it’s imperative to end the fast immediately.

If fasting is safe and starvation is unsafe, all you need to do is listen to your body. There are very clear warning signs. Once fat levels drop dangerously low, your body elicits an unmistakable and irrefutable hunger: one totally different from the kinds of hunger which often come and go throughout any water fast. If electrolyte levels become dangerously imbalanced, symptoms may include nausea, brain fog, cramps and other issues. Unfortunately, these symptoms can be almost identical to those which arise through normal cleansing. Often, only the context in which they appear provides the definitive clue, but a water fasting expert should be able help identify these, especially if they’ve been working with you throughout the fast.

5. Discomfort versus danger

In fasting as well as in the rest of life, discomfort and danger are clearly two entirely different issues. Detox symptoms may be uncomfortable, but this does not mean that they’re inherently dangerous!

The simplest analogy would be to consider the flu. Your muscles are aching, you feel a little nauseous with a headache to boot. You’re certainly in discomfort, but is it dangerous? Of course not!

Essentially, flu often presents exactly the same spectrum of symptoms (with the exception of fever) as you might experience on a water fast. Why? Because in both cases your body is detoxing. The only question is whether you’re cleansing from a virus or from the toxins released through the fast.

6. Danger arises when brain overrides body

Fasting becomes dangerous primarily when we allow our mind to dictate what it thinks is best for our body. If, in contrast, we simply tune into the messages our body is continually sending us throughout the fast (as well as every day of our lives), and if we act accordingly, then we have nothing to fear. Body knows best.

Here are two classic examples.


Many people follow a protocol of drinking at least ‘x’ litres or fluid ounces per day during their fast – in other words, they aim to reach a ‘magic number’ formulated in the brain, not the body. We’ve all heard about how it’s important to stay hydrated. There’s a certain logic in this. If you’re water fasting, the water helps to flush the toxins out from the tissues. So surely more is better. I even know of one medically supervised water fasting centre in the US which prescribes their patients a minimum of 140 fl. oz. of water per day. That’s over a gallon!

The problem is that drinking more than you actually require slowly washes out electrolytes. (Exactly the same issue can play out in endurance sports. No-one dies from dehydration during competition, but there have been occasional cases of marathon runners suffering sudden death from hyper-hydration.)

Considering that electrolyte depletion is already one of the dangers in an extended fast, drinking too much should definitely be avoided. The immediate solution, however, is not to take an electrolyte supplement. (as many people naturally assume). This only kicks the can further down the road, correcting for one bad mental decision by introducing yet another variable into the equation. No. The solution is simply to follow your thirst.

Thirst is there for a reason. It’s your body’s way of telling you to drink! I always recommend that my clients use thirst as the default setting to determine the quantity of water they drink, and nine times out of ten things run perfectly. On the odd occasions that problems arise, sometimes the solution is to drink more – but, equally, sometimes it is to drink less. It all depends on which particular symptoms appear in the body.


As mentioned above, ignoring the body’s warning signs can get you into trouble, causing danger. But what does this really mean? It means that your mind overrides a particular bodily symptom, in a decision to ‘push through’ the fast.

Sometimes you do need to push through a particularly acute wave of detox. Other times you need to abort the fast. At times it can be exceedingly difficult to know which is which, and what the right thing is to do. The ultimate decision, though, should not be based on willpower (a mental attribute) but rather trying to tune into what your body is feeling. I’ve had clients suffer through truly horrendous detox symptoms, and although they’ve wanted to stop (a mental state), deep in their body they’ve known that continuing the fast was the right thing to do. Similarly, I’ve known cases where the actual physical symptoms were quite mild, but the person concerned drove straight to the ER because they just knew deep in their body that something wasn’t right. It’s in cases like these – in which physical discomfort can make it difficult to objectively observe yourself – that an external expert opinion can prove indispensable.

Check out the webshop on

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

7. People for whom fasting is not safe

Although water fasting is completely safe for well over 99% of the population, there are nevertheless exceptions to the rule. It’s extremely important to understand which conditions and situations preclude fasting! These are listed below:

Cardiac issues

The only cases I’ve heard of which have ultimately resulted in death concern people with underlying heart problems. This does not rule out fasting per se, but it’s crucial that anyone suffering from such a condition discuss it first with their doctor.

There are two potential complications caused by a weak heart. First, cleansing puts a strain on the heart. In the same way that people experience a pounding heart during the flu, a very similar symptom can present while water fasting as well. This can be further compounded if blood pressure falls excessively. (Otherwise, lower blood pressure is a perfectly normal mechanism of a water fast which facilitates detox.) Although an elevated heartbeat is perfectly safe for the vast majority of people, it could eventually cause problems for someone with cardiac issues.

Second, if electrolytes fall too far out of balance, this can ultimately lead to cardiac arrest. A whole array of symptoms makes itself increasingly obvious before finally reaching this point, but if the body’s warning signs are repeatedly ignored, then consequences are inevitable.

Type 1 diabetes

Those with Type 1 diabetes are usually told they cannot water fast under any circumstances. This can be true if pancreatic function is already too diminished. Nevertheless, water fasting is certainly possible in certain cases, and I myself have worked successfully with Type I clients. Before considering such a fast, though, it’s imperative that anyone with Type I diabetes discuss it first with their doctor.

In contrast, Type 2 diabetes usually responds extremely well to water fasting. This is the type of diabetes most of us are more familiar with, involving the body having built up resistance to insulin, as opposed to damage to the pancreas (Type 1). Since the issue here concerns hormonal imbalance rather than physical dysfunction (as in Type 1), a water fast’s hormonal reset often leads to a full healing of the disease.

Toxic drugs and medications

If you’re taking prescription medication immediately before your water fast, you’ll need to decide whether to continue with your meds, reduce dosage or come off them altogether during the fast. This is an issue which should always be discussed with your doctor as well as a fasting expert, so you can find a solution which maximises the healing potential of your fast while keeping you safe.

Certain drugs and medications can cause nasty detox symptoms at the best of times. In everyday life, this can mean both side-effects while taking them, as well as withdrawal symptoms afterwards. Coming off such drugs ‘cold turkey’ and diving straight into a water fast can make things much, much worse. In such cases, the fast is too powerful, the rate of detox is simply too high, and the body can become overwhelmed – possibly leading to death. Alcohol, opiates (such as Methadone) and certain anti-depressants (such as benzodiazepenes including Xanax and Valium) all fall into this category.

As much as coming off your meds for a fast might be a problem, the opposite can also be true. For instance, certain common drugs used for Type 2 diabetes, such as Metformin, block the liver’s gluconeogenesis (the process of synthesizing glucose). This can cause serious complications because the metabolic circumstances during a water fast are almost the opposite from those in everyday life – that is, from the circumstances for which the drug was prescribed in the first place. In short, Type 2 diabetics normally benefit from lowering the level of glucose in the blood through a drug like Metformin. This is because Type 2 diabetics do not respond effectively to insulin, which would normally fulfil this function. During a water fast, though, glucose levels are already significantly lower than in everyday life. This means that a drug like Metformin can force the body out of homeostasis, making a water fast highly dangerous.

Psychological imbalances

For almost everyone, eating goes well beyond the purely physical realm of simply fulfilling nutritional requirements. Of course, we also eat for emotional reasons, in order to feel comfort, to relieve boredom, to calm anxieties. Since psychological imbalances all express themselves through various painful emotions, a water fast inevitably impacts further on those same emotions.

It’s often a double-edged sword.

On the one hand, taking away the comfort of food and all the other emotional crutches of eating can prove exceedingly difficult for those suffering from psychological imbalances. This holds especially true for those with eating disorders – the vast majority of which are primarily psychological based and not physical.

On the other hand, it’s also true that many psychological imbalances are caused by hormonal imbalance – and one of the best ways to restore hormonal equilibrium is through an extended water fast. In such cases, healing the hormonal imbalance also heals the root of the psychological imbalance. In the 19th century, for instance, water fasting was even used to successfully heal schizophrenia.

Rare metabolic disorders

There exists a very small number of rare metabolic disorders which makes water fasting impossible. Most of these involve the inability to switch over to ketosis once glycogen stores are exhausted. Fortunately, the body provides extremely clear warning signs. Severe nausea and vomiting in the first 24-48 hours of a water fast almost always indicate that the fast should be aborted, regardless of the underlying cause.

Fasting with any medical issue

Above and beyond the medical issues described here, it’s always best to discuss any health conditions you may have with both a medical doctor and a fasting expert before embarking on a water fast. This holds true for any fast longer than 24 hours, and is especially important for fasts over 3 days. It’s always better to be safe than sorry!

Refeeding and eating

It may come as a surprise, but the most dangerous part of a water fast isn’t the fast itself but rather refeeding and eating afterwards. This applies especially to fasts of approximately 10 days and longer, in which so-called Refeeding Syndrome can develop.

Refeeding Syndrome can occur as the body shifts away from ketosis and back to a primarily carbohydrate-based metabolism. In order to manage this transition, the minerals potassium, magnesium, phosphate and vitamin B6 play a decisive role in shifting position and changing their biochemical function within each cell. The problem develops if you eat too many calories too soon, because these minerals will not have arrived at their new ‘destinations’ and therefore will not be able to perform the functions required of them. The initial stages of Refeeding Syndrome cause oedema and cramping, especially in the fingers and toes. If calories are not restricted at this point and the body’s warnings signs continue to go unheeded, this can eventually lead to nausea, heart arrhythmia and finally cardiac arrest.

I would venture to guess that about half of all people who undertake an extended fast experience the initial stages of Refeeding Syndrome during the first few days of refeeding. I certainly did myself on several occasions, before I understood what was happening! Although potentially life-threatening, Refeeding Syndrome is nevertheless something that most people pass through without any serious problems.

In addition to Refeeding Syndrome, the other main issues during the refeeding period concern digestive problems – which, again, are usually caused by eating too much too soon. There are two dangers: overloading the GI tract before it is capable of (1) producing the requisite enzymes for digestion and (2) physically moving the food through the intestines (peristalsis). As with Refeeding Syndrome, digestive problems tend to occur on longer fasts, in this case from about a week or longer.

One final problem caused by eating too much too soon is that the ‘wrong kind’ of fat can start accumulating. Instead of gaining normal subcutaneous fat – the kind most people notice around their waist line and elsewhere – the body prioritises fat around the inner organs in the period after a fast. This is the kind of fat which, in higher quantities, has been linked to an increased likelihood of chronic disease in general.

If you need help in designing your own refeeding program, I offer a pdf in the shop here. Alternatively, my water fasting clients receive a personalised refeeding plan through daily video calls, as part of full coaching.

Refeeding pdf (67 pages)

After you break an extended fast, it’s extremely important to follow a well structured meal plan.

If you return too quickly to a normal diet, you risk encountering both digestive problems as well as ‘refeeding syndrome’. This is a potentially fatal complication caused by the change from ketosis back to your everyday metabolism. After an extended fast, the body cannot be rushed in this process.

If you have any doubts, I offer a downloadable 67-page PDF which covers refeeding for any length of fast.

9. Final thoughts

Although this article is starting to read like a water fasting horror story, the truth is that nothing could be safer in the whole world. The real horror story revolves around eating – and especially so in the modern Western world. Bad eating habits cause obesity, diabetes, cancer, cardiovascular disease… The list goes on and on. If the number of documented deaths through fasting over the last century can be counted on the fingers of one hand, how many millions of deaths can be traced each year to eating? Try Googling that!

Or just trust in yourself and in your body’s innate wisdom, and fast.

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8 responses to “Is water fasting safe?”

  1. Great. I know where you are coming from now. One last question about cost. I am assuming bloodwork is not included and I am also assuming Medicare won’t cover it. Would you be able to tell me what bloodwork is necessary and how often so I can get cost. Then I would be ready to schedule a consultation and move forward.

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

      Hi again Loretta,
      No, I don’t include bloodwork in the price because I usually don’t require it. It’s something we’d discuss in the initial consultation before the fast, but the fact is that humankind has been fasting safely for millennia without getting any labwork done at all. It’s not that I’m against bloodwork – far from it! All information is good information! However, fasting symptomatology usually shows up any issues long before anything shows up in bloodwork, which usually simply serves to confirm the obvious. The main exception to this is potential electrolyte depletion (especially regarding potassium or sodium). Although this occurs only rarely – and in my experience only towards the end of 40-day fasts – it IS a potentially dangerous issue. A simple electrolyte panel taken at around the 30-day mark can give peace of mind and removes any doubt about problems occurring later in the fast. The other case in which bloodwork is advisable concerns people suffering from absorption issues, but this would be discussed in the single consultation. However, I’m always happy to go over bloodwork with clients who prefer to take regular blood tests during their fast.
      Hope this helps,

  2. IH is short for idiopathic hypersomnia. As far as credentials— what is your Doctor of Philosophy in? Did you intern at a fasting clinic? Or are you self taught with reading and supervising your own and others fasting? I just want to get a feel for your educational background whether it is experience or schooling. No doubt you have knowledge as indicated by the articles on your website. Thanks.

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

      IH is also short for intracranial hypertension :-), so thanks for clarifying your case.
      In terms of my knowledge of water fasting, I’ve done it the old-fashioned way: through 15 years of personal experience. Honestly, there’s no substitute. My D.Phil. from Oxford was in musicology, and as a lecturer and academic researcher I gained all the skills needed to delve fully into the theory and physiology behind fasting. In clinical practice as a coach, though, it’s mostly the years of personal experience which make the difference. Hopefully that shows!

  3. My husband has a super high arch and was a runner in high school. I suppose that would be considered an injury. He is considering surgery.

    I have IH. I am reading a book on fasting by Steven Hendricks, a journalist, who put his IH in remission with a restrictive vegan diet and series of fasting.

    We are considering fasting, but would like to hear more about your credentials.


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

      Hi Loretta,

      Thanks for writing. Fasting could definitely be beneficial to you both. In terms of your husband, a lot is going to depend on the specifics of his physiology. In terms of Intracranial Hypertension (IH), fasting should bring both immediate and, depending on the length of your fast, long-term benefits due to the reduction in inflammation experienced during the fast.

      If you’d like credentials, I refer you to (1) Google reviews and (2) the Testimonial page of this website:



      Hope this helps,

  4. Tallis, have you had any success working with individuals with idiopathic hypersomnia or Morton’s neuroma?

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

      Hi Loretta,
      Thanks for your question. No, I’ve not worked with anyone trying to heal from those issues. Given that Morton’s neuroma is often caused by a physical injury, I suspect that water fasting would be quite effective at addressing it. Given the uncertainty concerning the cause of idiopathic hypersomnia, it’s much harder to guess. Given that sleep patterns are ultimately driven by hormonal patterns, I suspect that you’d have to think about 21+ days in order to make significant progress (and especially without knowing more about your earlier background).
      Hope this helps,

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