Welcome to my science-based guide that will take you through the most common dangers of water fasting.

You will see the research on the most common types of issues that you could potentially run into (headaches, postural hypotension, gout, stomach pains and cramping).

We will also take a look at the dangers you could expose yourself to, if you did extremely long water fasts (depletion of body fat reserves or protein reserves).

Before we dive in, here's a brief overview of everything that I've covered in this part of my water fasting guide (use it for easier navigation).


One of the more common dangers of water fasting is developing a headache.

But scientific research[1] has three pieces of good news for you when it comes to fasting headaches:

  • the headaches only happen to a small number of people during water fasting (so it's likely you may not get them at all),
  • they are very likely to happen in a mild or vague form of a headache,
  • and the headaches are very likely to disappear after a while (even if you don't break a fast).

All in all, these types of headaches aren't particularly dangerous or persistent, so let's move on to another common condition that can develop during water fasting.

Orthostatic hypotension

Orthostatic hypotension, also known as postural hypotension, is one of the most common dangers of water fasting[2].

Orthostatic hypotension means that your blood pressure drops, if you stand up from a sitting or a lying position.

In most cases, this triggers a feeling of lightheadedness or dizziness that passes away quickly.

But in extreme cases, orthostatic hypotension can cause you to faint.

This isn't dangerous in and of itself, but you could hurt yourself if you actually collapsed to the ground.

You can find more details on how to prevent (or deal) with lightheadedness and dizziness in the part of my water fasting guide that explains all about how to do a water fast.


Gout is another potentially dangerous condition that can happen to you during water fasting.

You can recognize gout as sudden pain in your joints (usually in your toe joint, but it can also affect other joints in your body).

Most likely, gout develops because of increased production of uric acid during water fasting, and shouldn't be particularly dangerous.

If gout happens to strike in the middle of a fast, it should also start fading away quickly (and completely disappear after a while).

But if it doesn't, then you should end the water fast right away.

Because, according to science[2], gout symptoms disappear as soon as the water fast is broken.

On to another danger of water fasting that you can run into after you already end your water fast.

Stomach pains and cramping

In one recorded case, a "professional faster" ended a 30-day water fast with fruit, one of the most easily digestible foods on the planet.

But because he ate a little bit too much, he had to deal with some pretty severe stomach pains and cramping for a while[3].

Now, 30 days is an EXTREMELY LONG water fast.

And you should never fast for more than 3 days / 72 hours on your own (unless you can fast in a specialized facility under medical supervision).

So if you only fast for a couple of days at a time, it's highly unlikely that you'll run into stomach pains and cramping.

In fact, you'll probably be able to return to your old diet very quickly.

But if you fasted for a week or more (under medical supervision), then you'd need to slowly transition back into your normal diet.

The general rule is, the longer you fasted, the more careful you need to be about how you break the fast.

Let's continue with some of the life-threatening dangers of water fasting.

Depletion of body fat

Yes, while water fasting can be highly beneficial to your health, if you take things too far, fasting turns into starvation.

And voluntary or not, when starvation is taken too far, it results in death.

I know you will never, ever put yourself in the way of this particular danger, because you will fast for no more than 3 days / 72 hours at once (unless you can fast under strict medical supervision).

But let's just look at the science on this, so you can see how seriously wrong water fasting can be, if you take it too far.

Some early research has estimated that the maximum limit for lean, healthy, 25-year old men, before they died of starvation, was 60 days[4] (though one of the men the research included, died after only 45 days of water fasting).

The scientists calculated this happens when 70%-95% of body fat reserves have depleted.

However, death from starvation doesn't only happen when your body fat reserves drop too low.

The research you just saw only looked at the deaths of lean people, who wiped out their body fat reserves way sooner than they exhausted their body's protein reserves.

So, let's take a look at another type of danger that overweight and obese people would expose themselves to if they did an extremely long water fast.

Depletion of protein

You see, with overweight and obese people, the situation is completely reversed.

While some obese people have enough energy stored in their body fat reserves to survive for a very long time (3-6 months), extremely long water fasting poses a different danger to them.

And that's death by starvation because they would wipe out their protein reserves.

And because their body fat stores are so huge, that could happen long before they've run out of body fat reserves[5].

Again, if you do a water fast shorter than 3 days / 72 hours on your own (and only do longer, medically supervised fast in a fasting retreat), then you'll be absolutely in no danger form death by starvation.

But I feel the need to explain this is possible, because I've seen many people in the fasting community argue that they could fast for months at a time, simply because their body fat reserves are so large.

So don't develop a false sense of confidence that you can survive on nothing but water for as long as you have enough body fat left (you can die from wiping out your protein reserves as well).

Summary (actionable takeaways)

In this part of my science-backed guide, we looked at the dangers of water fasting.

You saw the scientific evidence that says:

  • the minor dangers of water fasting include headaches, postural hypotension, gout (all of these should not come in extreme form and should fade away quickly),
  • there is a minor danger of developing stomach pains and cramping after you break a fast, but if you keep your fasts short and don't overeat as soon as you break the water fast, you should be fine,
  • that water fasting for extremely long periods of time (45-60 days at once) could actually lead to death by starvation (because you could run out of body fat reserves),
  • that ever if you have large reserves of body fat, you should not expose yourself to the dangers of prolonged starvation, because you could run out of protein reserves (which can cause death even if you still have a lot of body fat left).

Written by

Rok Sprogar is a NASM Certified Nutrition Coach (NASM-CNC) and a NASM Certified Weight Loss Specialist (NASM-WLS) who has been contributing highly actionable and science-based content to Leanhigh.