The Starvation Diet

My Five-Day Water Fasting Experiment

Last week, I went five full days - Sunday to Friday evening - without eating a single calorie. Am I anorexic? Hopelessly poor? Insane? I can assure you that I’m neither anorexic nor poor.

It’s called water fasting. As the name implies, the idea is to put nothing down your gullet except fresh water for several days or more. Supposedly, this comes with numerous health benefits.

I realise this falls outside much of the conventional wisdom about health. But then, the conventional wisdom about health is why nearly a third of British adults are obese. So who cares what conventional wisdom has to say?

What’s the point?

The basic idea is that a few things happen when you fast.

Firstly, it encourages a process called autophagy, whose name comes from the Greek for ‘self-devouring’. This is the body’s natural process for killing off old and decrepit cells to make room for the new, and it’s essential to health.

Secondly, after a few days without food, your body enters a state called ketosis, which essentially means that you’ve run out of carbs and start burning fat for energy. This has obvious fat loss implications - although I didn’t do this for fat loss, as I didn’t have much to lose.

More importantly, evidence suggests that periodic fasting can lower your risk of cancer, Alzheimer’s, Parkinson’s, and more. I recommend this post by Nat Eliason, which has (among other things) a nice roundup of the supposed benefits and the evidence.

Think about it like this: humans aren’t supposed to eat the whole time. We’re adapted to life on the African savannah, where there was no guarantee of a steady food supply. Short periods without food are definitely something we’re adapted to handle - and arguably something we’re supposed to experience every now and then.

Plus, numerous friends and acquaintances of mine have tried it, and all reported positive results. The consensus I’d heard is that the first 2-3 days can be tough, but after that it’s surprisingly easy. As well as the long-term health effects, you can see major upsides while fasting - the biggest one being an enhanced state of mental clarity.

And finally, it’s just plain weird. So of course I’m intrigued. And at the very least,it’ll give me something to write about.

Reasons Not To Water Fast

I’m not a doctor. Do your own research before doing any kind of fast yourself, and don’t blame me if something goes wrong. Before I give any kind of advice, there are some obvious “not to-dos” worth pointing out. Don’t fast (or at least consult your doctor first) if you’re:

  • Ill or have any major health issues.

  • Severely underweight.

  • Pregnant.

  • Are young and still growing.

  • Probably some other obvious contraindications that I’m missing.

I fasted for five days; next time I’ll probably do seven. (Some people have done them for a month or more.) If you want to do a particularly long water fast, you should probably do it under medical supervision. A “fasting centre” - yes, they exist - is just a web search away.

Let’s be clear about this: people die if they put the wrong things into their body, including “nothing”. If you’re otherwise healthy, a 5-day water fast probably won’t kill you, but you still need to take this seriously. Do your homework.

Above all, listen to your body. If things start getting really tough, quit! Better safe than sorry.

Common side-effects of a water fast include fatigue, headaches, and muscle cramps. If you’re addicted to caffeine and/or sugar you can expect to feel withdrawal effects from those substances too. You don’t have to throw in the towel at the first sign of discomfort - but don’t force yourself through extreme negative symptoms just for the sake of completing an arbitrary number of days.

How To Do a Water Fast

The basic rules of a fast are this:

  1. Don’t eat anything.

  2. Drink only water.

The devil, however, is in the details. As with anything health-related, no-one can agree about anything, and there’s a ton of contradictory advice out there.

For every article online that advises one thing about fasting, you can find another that advises the opposite. And of course, for every credible-seeming source with the appearance of science, there’s page after page of hippie mumbo-jumbo. (Hint: if it says anything about “detoxing” or “cleansing”, you can probably ignore it.)

1. Don’t eat anything?

Some sources recommend you supplement with minerals like sodium, magnesium and potassium. These won’t get your digestion going because they contain no calories, and they can alleviate headaches and muscle cramps if you get them.

I didn’t take any magnesium or potassium supplements, but sodium can be found in regular table salt. When I had a headache on days 2 and 3, I occasionally dissolved a pinch of salt in the water I was drinking. My headaches eventually went away; I don’t know if it was the salt that fixed them.

2. Drink only water?

What kind of water should you drink? Is tap water okay? Or should you only drink distilled water? Mineral water? Holy water? No-one agrees.

In my case, the decision had already been made for me - here in Brazil you can’t drink tap water anyway. I drank water from the filter in my kitchen. (I would have drunk holy water, but it burns my tongue.)

Some say that zero-calorie drinks like tea or black coffee are also acceptable (providing you don’t mix them with sugar/milk/etc.). For the sake of purism I stuck with water… until day five, when I had a single cup of black coffee a few hours before breaking the fast for real.

So technically this wasn’t a “real” five-day water fast, but I’m not losing any sleep over it. Well, that coffee did get me way more wired than normal. So maybe I did lose a little sleep over it… but not in a figurative sense.

There’s also disagreement on how much water you should drink. My solution: I drank whenever I felt thirsty. Which was, “most of the time”. While I didn’t take exact measurements, I definitely drank a LOT of water during my fast. As you should.

Interestingly, I felt much less thirsty - and consequently drank less water - on the latter days of the fast than at the beginning. I’ll let the nutritionists speculate as to why this might be the case.


Everyone I know who’s fasted agrees on this: after the first day or two, you don’t feel hungry anymore.

To give a not-very-scientific explanation: after your stomach has sounded the alarm for a while but received no answer, it basically gives up. It realises that you need to go hunting and gathering, and it’s not in your stomach’s interest to cripple you with debilitating hunger pains while you do this.

On days one and two I felt hungry like you’d expect, but it wasn’t too bad. It came and went in waves, and it didn’t interfere with my ability to get other stuff done.

On day three I didn’t get hungry at all, although I felt bad in other ways as I’ll describe below. Day four was pretty easy, although my stomach did let itself be known for an hour or two in the middle of the day.

By far the easiest day, in terms of hunger, was day 5. I didn’t feel any cravings or hunger pangs whatsoever. When I broke the fast at 8pm, I felt like I could easily have continued. It’s amazing how little hunger I felt after 120 hours with no food.

For sure, I never felt full. On some level, I was always aware that my stomach was empty. I’d compare it to how I feel on a normal day if I’m slightly late to eat dinner - nothing I couldn’t deal with.

This fast made me aware of the different types of hunger that I feel. There’s a physical component - grumbling from the stomach - and a psychological one - cravings for the taste of food on my tongue. On days one and two, the psychological hunger was stronger; by day three it had disappeared and physical hunger was more noticeable.

Then there’s the habitual side of hunger. This is the weirdest thing about a fast: on practically every day of my life, I’ve eaten lunch and dinner at roughly the same time. It felt very strange to not do it anymore.

All day, every day, food-related thoughts kept popping into my head, only to be struck down mid-sentence. “Hey, maybe I should pop out and get a - oh, right, yeah.”

This was the hardest thing - skipping meals isn’t just hunger-inducing, it’s disappointing. After a solid morning or afternoon slogging away at whatever at is that you do, it’s rewarding to take a break and sink your teeth into something succulent. Except now, for the first time in your life, you can’t.


I didn’t really experience the enhanced mental clarity that some people report. Days two and five were probably the best, but I never at any point thought “wow! I’m so much more clear-headed than I normally feel!”.

On the other hand, I did experience some mild headaches on day two. This is a common side-effect, and there are many aspects of a fast that could cause it. Drinking water helped, as did eating a bit of salt.

Then I went to bed on day two… and woke up with a SPLITTING headache. Combined with a dry mouth, it felt almost exactly like a hangover.

You know when you desperately need water but feel too shitty to drag yourself out of bed and get some? That was my Wednesday morning.

When I did get up, I felt slightly nauseous - again, just like a hangover. I drank tons of water, and took more salt. By about 1pm, my worst symptoms had subsided, but I still felt very foggy and found it hard to concentrate on anything. Day three was, for all intents and purposes, a disaster.

Other days weren’t nearly as bad, but on the whole, fasting was a definite net negative to my productivity. Sometimes I felt clear and focused, other times I felt foggy and couldn’t concentrate. The latter was more common.

With that being said, the focus-to-fog ratio did improve as the fast went on. Day five was my most productive day; day six would likely have been better if I’d continued. This is one reason why I’m interested in trying a 7-day fast next time.

Fasting instilled me with a strange sense of apathy. I’m normally a type-A, “gotta be doing something productive”, always-on kinda guy, but most evenings last week I was content to just lie in my hammock and stare into space. I’d try to read a book, but the words just wouldn’t go into my head.

On Thursday, after trying and failing to read the same paragraph five times, I gave up and spent the evening playing video games - and I almost never play video games. Borderlands 2 seemed to be the only thing that would keep my brain occupied.

Sleep & Energy

I slept more than normal while fasting, averaging about 9-10 hours each night. Other than that, my physical energy levels didn’t feel very different from normal. Other than the occasional set of press-ups or jumping jacks, I didn’t do any exercise, but I was still able to go about life as normal - running errands, walking around town, etc..

I live on the sixth floor, and my policy is to only take the lift when I’m in a rush or carrying something heavy. While fasting, I upheld this policy. The stairs were more tiring than normal, but they weren’t insurmountable.

Most nights I’d go to bed much earlier than my normal time, even though I wasn’t very tired. “Hey, I’ve got nothing else to do. Might as well go to bed”. It was part of the same general sense of apathy described above.


On day three, I started getting a strange taste in my mouth - sweet, slightly metallic. This is another common side-effect of fasting, and it’s a sign that you’re entering ketosis (the state of burning fat for energy instead of sugar.)

The funny thing is, I recognised the taste. I feel the exact same taste in my mouth when I wake up after a particularly heavy night of drinking - especially if I’ve been drinking spirits.

I remember something from when I was 18/19 and still living at home. Sometimes after a night out, I’d be lying in bed feeling sorry for myself and I’d have this same sugary taste on my breath. My mum, who is a doctor, would observe my hangover and tell me - among all the typical parental anti-alcohol admonishments - that I “smelled of ketones”.

I had no idea what a “ketone” is, but now I know that it’s a type of molecule produced by the breakdown of fatty acids. When you’re in ketosis, you expel ketones when you exhale, hence the taste on my breath.

I still don’t understand what this has to do with alcohol.

Other stuff

Some other notable things that happened (or didn’t) while fasting:

  • I got slight cramps in my legs on day three. Again, this is a common side-effect. It may be caused by mineral deficiency. Whatever the case, it wasn’t too bad, and it lasted less than a day.

  • Throughout the fast, I felt very sensitive to cold. I’d sit at my desk wearing my thickest jacket and still be shivering - and I’m in Brazil.

  • My lips got very dry during the fast. Applying lip balm felt amazing. When you haven’t eaten in days, the smell of anything vaguely food-like is a pleasure.

  • Some report feeling light-headed or dizzy while fasting. This wasn’t really the case for me; sometimes I’d feel a bit light-headed after standing up, but it wasn’t anything major.

Breakfast (literally)

On Friday, I was practically counting down the minutes until I could eat again at 8pm. The closer it got, the slower time seemed to move.

Some argue that you should reintroduce food slowly when breaking a fast - start with the stuff that’s easy to digest, then slowly work your way up to the tougher stuff like meat. I question this logic, and I didn’t really bother.

I think Nat gets it right here (and I second his recommendation of Antifragile:)

If you were in the wild, and you hadn’t eaten in four days, and you managed to kill a deer, you wouldn’t go forage for berries before eating it to “work yourself up to it.” You’d eat the damn deer.

Also, occasional shocks are good for your body, that’s the whole point of fasting in the first place. If you treat your body like glass then it will stay like glass. This is the same logic behind body building, hormesis, vaccinations, cold therapy, and any other process where we inflict small damages to increase the strength of the system (what Nassim Taleb calls “Antifragility”)

When the time came, I wolfed down a pack of nuts with a total lack of table manners. It felt amazing.

Then my girlfriend got home from work and we went out for dinner. Unfortunately, we weren’t sure where to go and ended up in a crappy little bar/restaurant called Vitrine where I ate the most disgusting burger I’ve ever tasted.

This “restaurant” was so bad it makes me angry. The food was barely edible, the wine was even worse, and don’t get me started on the service. It’s hard to think of a single positive thing to say about the whole experience beyond “the food didn’t literally kill me” and “the building wasn’t on fire”. The only thing I enjoyed was leaving. What an awful reintroduction to the world of eating.

So if you take one piece of advice from this post, let it be this: never go to the restaurant Vitrine on Rua Augusta in São Paulo. Oh, and you might want to try water fasting too.