You can read about my previous 5 day water fast experience here.

Only drinking water with no food at all for 10 days sounds crazy at first thought.  I thought the same.  However, upon further research and experimentation, I found that it is incredibly beneficial both physically and mentally.  Let’s get a few common questions out of the way to start.

What is a water fast?
A water fast is where you don’t eat and only drink water for a set period of time.  Most humans can survive 40+ days without food, and virtually everyone can go two weeks without food with no problems.

Why do a water fast?
Water fasting has many great health benefits (see ‘Benefits’ below).  In short, it improves the respiration of your cells which makes them function more effectively, it greatly strengthens your immune system, removes toxins from you body (detox), starves potential cancerous cells, shown to increase longevity and helps repair chronic injuries as well as gut issues. There are few downsides other than the discomfort you have at first and the short time spent not enjoying food.  An extended fast can greatly improve the quality of your life and improve how your body functions, as well as change your outlook on food in general.

Will I lose muscle?
A little bit, depending on how you fast.  Most muscle loss happens within the first 3-4 days of the water fast.  Once in ketosis (where your body produces ketones for energy rather than glucose (blood sugar)), your body goes into protein sparing mode and you lose very minimal muscle.

How much weight will I lose?
While I wouldn’t recommend fasting to lose weight, you will lose a fair bit.  During my 5 day fast, I lost 5kg (11 lbs) in 5 days.  During my 10 day fast, I lost nearly 6kg (13.2 lbs), most in the first 5 days.  The vast majority is water weight which will be gained back within 1-4 weeks after the fast, assuming you eat the same diet as you did before the fast.  Fasting is a great way to reset your diet if you plan to make bigger changes in your life, and the weight can stay off.

Why not juice fast instead?
Juice fasting has benefits as well, though I’m not experienced with it.  The goal of water fasting for me is to reach ketosis as quickly as possible and stay there (where you get the benefits mentioned below).  Because juice is more often than not just sugar water (all the fiber from the fruit/veggie is removed), you likely don’t hit ketosis, and if you do, it wouldn’t be as deep.  Juice fasting and water fasting are entirely different.  This post is entirely about water-only fasting.

What is ketosis?
When you normally eat, what you eat is converted into glucose which goes into your blood and provides energy to your body (brain, muscles, etc.).  When you don’t eat, you utilize most of the remaining glucose in your body, and then your body begins to metabolize fatty acids in the liver to produce ketones.  Ketones are an alternative form of energy you use when fasting which the body uses very efficiently – the brain loves them, the cells love them, and the heart loves them – they actual prefer them (fatty acids are the hearts main resource for energy).  When your body is primarily using ketones for energy, you’re in a state of ketosis.

Will I be productive when I fast?
During a 10 day fast, at least the first 5 days you won’t feel like doing much, so it’s best to keep that time to rest/relax.  After day 5 you’ll still feel physically weak and have low blood pressure (can’t stand up too fast), but you’ll likely be quite motivated to work, read, learn, or otherwise do things (when in ketosis, you’ll mentally feel really good and clear-headed).  You’ll have the energy to walk around and socialize.  If you can’t get 5+ days off to rest, start with a 3 day water fast over a weekend, or a 5 day fast starting on a Thursday and ending on a Monday.

Benefits of Water Fasting

There are many benefits.  So far studies and experiments are showing very positive signs, demonstrating that water fasting is an incredibly healthy thing to do.  I’ve listed a few of the benefits below:

  • Greatly strengthens your immune system by regenerating new, healthy white blood cells (Source).
  • Reduces risk for heart disease by reducing triglycerides and increasing HDL levels.
  • Improves cardiovascular health – lowers blood pressure, improves heart function.
  • Cellular repair – when we’re sick, why do we lose appetite? Because our body wants to spend energy repairing itself, not digesting food.  When in ketosis, the respiration of our cells (how they utilize oxygen) improve, allowing them to function properly. (Source)
  • Reduces cancer risk (Source)
  • Increases longevity – caloric restriction likely increases your life expectancy (Source, SourceSource)
  • Reduces inflammation (high inflammation can cause heart disease, cancer, arthritis ) (Source)
  • Increases cognitive clarity – the brain loves ketones and you think clearly while in ketosis. (Source)
  • Helps heal insulin resistance (80+ million Americans have it) – See lecture here.

Tips When Water Fasting

Educate yourself about the benefits and side-effects of fasting beforehand so you know what to expect and are convinced that what you’re doing is a good thing.  The fast will likely be mentally challenging.

  • Drink lots of water, the highest quality you can.  Water with natural minerals in it is a bonus.
  • Pinch a bit of salt into your water to replenish sodium that is rinsed out when fasting.
  • Get an hour of sun exposure each day during your fast.  It speeds up your metabolism and relaxes your mind, getting you out of the house.
  • Eat the ketogenic diet for at least 5 days prior to fasting to help ease the transition to ketosis (the body transition from glucose to ketones for energy can feel like the flu).
  • Have black coffee (no sugar or calories) on day 1 if you want to help curb your appetite, though keep it limited.
  • If you can, do it with a friend – hold each other accountable and chat about your experience.
  • Measure your ketone levels – it gives you motivation to keep going.
  • Expect it to be hard, but know it’s a mental game!

Common Kinds of Fasting:

  • Intermittent fasting – restrict your daily eating window to an 8 hour period (ie. from noon-8pm).
  • 24 hour fast – don’t eat for 24 hours (ie. eat dinner, and don’t eat again until dinner the next day).  You can do this anywhere from once a month to twice a week.
  • Alternate-Day Fast – Don’t eat (or severely restrict your calories) every second day. On eating days, eat as much as you want.
  • 3 day water fast – Don’t eat for 72 hours.
  • 5 day water fast – Challenging both mentally and physically.  Because it takes roughly 72 hours to reach ketosis, you’ll be in ketosis for approximately 48 hours.
  • 7 – 10 day+ water fast – The longer the fast, typically the more benefits.  However, there is a tradeoff as it isn’t a very enjoyable experience.  During my 10 day fast, I reached ketosis during day 1 because I did the ketogenic diet prior.

My Experience

I’ve done intermittent fasting for years now as a way to restrict my feeding window, and it has many benefits itself.  I’ve also done many 24 hour fasts throughout the last several years, which are quite easy for me now (the more you fast, the easier it becomes).

About 1.5 years ago I did a 5 day water fast – you can see my report here which has some useful information on fasting.  During my 10 day water fast, I decided to do a few things differently.  Because of the difficulty in transitioning from glucose to ketones for energy during the previous fast, I decided this time around I would eat the ketogenic diet prior.  The ketogenic diet is basically where you get your energy from mostly fats, with some protein and little or no carbohydrates.  This is because fat doesn’t break down into glucose, it is metabolized in the liver into ketones.  This diet has shown to have lots of useful benefits, but my reason for doing it was to get into or close to ketosis prior to starting my water fast.

For 7 days, I ate almost entirely fat and protein. I started the water fast the following day, already 3.9mmol/L into ketosis, and 36 hours in was already at 8mmol/L, a deep level of ketosis where you’re body is producing a lot of ketones which are in the blood for energy, and is the therapeutic range of ketosis (listen to this podcast episode).  Comparing this to my 5 day water fast, I probably didn’t reach this level of ketosis until day 4, which means I spent roughly 48 hours in this range, while on the 10 day I spent roughly 9 days in it.  In fact, during my 10 day fast I was often at the 10mmol/L range, which is even better (more ketones in the blood).

In short, ketones are incredibly energy efficient, and improve the respiration of the cells.  This means your cells work more effectively in how they use energy.  The longer you’re in ketosis, the longer your body has to improve and detox itself.  If you want to read more on the in depth science of it, please watch this lecture.

The other difference in my 10 day fast was that I took BCAAs (branch-chain amino acids) during the first 24 hours to reduce muscle loss, as well as did some pushups to keep the muscles active (and had 1 coffee with a tablespoon of coconut oil).  Each day during the 10 days I did a small amount of stretching and reaching my hands in the air which fatigued my arms, chest, and back a bit, telling the body that I’m using these muscles.  It seemed to help, though it’s hard to measure with water weight loss.

The last differences where that I got ketone strips to actually measure ketone levels in the blood throughout the fast, and spent roughly 1 hour in the midday sun during 8 of the 10 days of the fast.  Sun exposure helps speed up your metabolism, and when in ketosis, this helps increase the number of ketones in the blood, which was my goal in that it is where the real health benefits happen.

Note: After my last 5 day water fast I didn’t get a cold or any sickness for over a year (I used to get sick every month or two before I fasted).  I suspect the 10 day fast will greatly strengthen my immune system as well.

Sleep: During my 10 day water fast, I had trouble getting to sleep often but once asleep I slept well.  I don’t recall dreaming once.  I also seemed to need less sleep – woke up with energy on 6-7 hours of sleep most nights.  This makes sense as my mind and body are telling me to search for food.

I kept a short diary of my fast, which you can find below.

0-24 hours (Day 1)
Weight start: 77kg (started 7:20pm on Sun, Jan, 29th, 2017).
I started at 7:20pm after my last dinner, which was grilled chicken and grilled pork (ketogenic diet).  I slept around 10pm, and woke around 7:30am as usual (9.5 hours).  This day was easy.  Since I do a 24 hour fast quite often, this was normal.  I did a 20 minute run and lifted some weights, then spent an hour in the sun.  Normal day. Had BCAAs and a bit of coconut oil to help with the transition to ketosis.  Also had coffee in the afternoon.

First night slept fine, as expected, considering that I had my last meal just a few hours before.

24-48 hours (Day 2)
About 20 hours in I was 3.9 mmol/L as measured via the ketone strips. 36 hours in, first thing when I woke up, was 8mmol/L.  I didn’t sleep super well the second night.  I had coffee around 4pm and I’m not sure if that contributed, or maybe it was just due to the fast. I napped this day by the pool and felt a bit better.  I felt a bit weak, but otherwise fine.

Started adding salt to water to help replenish sodium. When fasting, your body stops producing insulin (because your blood sugar stays low) and causes body to release sodium.  Hence why water weight loss is dropped rapidly at the beginning of a fast.  During my 5 day fast I didn’t supplement with salt and I suspect this caused muscle pains and headaches which were uncomfortable (I didn’t experience these at all really during my 10 day fast). Adequate sodium is really important – low sodium causes headaches, dizziness, muscle aches, etc.
Weight: 76kg (-1kg)

48-72 hours (Day 3)

Sat around watching Youtube lectures.  Feeling physically weak, but mentally okay.  Can’t stop thinking about food even though I’m not hungry – a bit annoying as it distracts me from doing all the mental tasks I want to work on – writing, practicing memory, watching lectures, taking notes, etc.
Weight: 74kg (-3kg)

Day 4
Had a hard time sleeping.  Took 1-2 hours to actually get to sleep, then woke up in the middle of the night to pee.  Have to get up slowly as my blood pressure is low. Napped mid day. Felt a bit hungry, and physically quite weak though mentally fine.
73kg (-4kg)

Day 5
Slept in until 11am, slept a good 12 hours.  Took me about 30 minutes to fall asleep but slept well. First time the entire fast I slept more than average (normal is 9 hrs). Yesterday and today have have had slight hunger pains but otherwise feel well. The last 5 days seemed very long and not looking forward to the next 5, though confident I will make it.  Urine is often yellow, drinking 3-4 liters of water per day with a pinch or two of salt into each 1.5L bottle.
Weight: 72kg (-5kg)

Day 6
My girlfriend was home so it was much easier to pass time rather than being alone. We drove around as she wanted to eat at a seafood place. Watching her eat and smelling the food was quite enjoyable. At 10mmol/L ketosis, where I’ve been for 2 days now. Had some hunger pains for a few minutes at a time throughout the day. Mentally fine, but physically weak still – have to walk slow. If I stand up too fast I’ll feel like passing out, otherwise I feel normal, especially if I’m sitting or staying still.
Weight: 72kg (-5kg)

Day 7
Slept bad this night. Took 2+ hrs to fall asleep as all I could think about was good food, especially the perogies from Poland – spinach filled with blue cheese sauce. Literally got up, went out to the couch and looked at food pictures.  Sounds like torture but it was on my mind.  Woke after 8 hours of sleep or so, still around 72kg. 10 days seems like forever. Time passes slow when you’re in it, in part because you’re always reminded of being in it, and counting the days.  I’m almost done with day 7, but I really have 3 full days left since 8, 9, and 10 are left.

Day 8
Slept decently well, took about an hour to get to sleep and slept around 7.5 hrs. Felt basically the same as yesterday, weight roughly the same (hard to say exactly with water consumption and urination), but right around 72kg. Got 1 hr of sun.

Day 9
Again took an hour or 2 to fall asleep, up at 8am. Urine dark. Have lots of motivation and feel generally better.
Weight: 71kg (-6kg)

Day 10
Slept early for the first time – around 9:30pm, and woke early, at 6am, about 1.5 hrs earlier than normal.  Overall felt like while fasting you need less sleep.
Weight: 71kg (-6kg)

I broke the fast at 7:20pm on February 8th with some fresh fruit – papaya, pear, and melon.  Also had 2 glasses of diluted juice.

Post-Fast Summary

Breaking the fast correctly is incredibly important both for your mental and physical health, but also for the process of detoxing.  The days while you begin re-feeding is when your body again begins to produce bacteria in your gut, enzymes in your stomach, regenerates white blood cells, etc.  Because your metabolism will be slowed, it is important to eat specific foods for the first several days to a week.  This should include easy to digest, high nutrient dishes like fresh fruit (watermelon is excellent), steamed/blended vegetables, yoghurt without sugar, avocado, etc.  Avoid processed food and refined sugar, and ensure you eat very healthy – it will pay off in the long run, even if you’re craving a strawberry donut.

Expect diarrhea within the first 12 hours of re-feeding.  I didn’t shit for 11 days while water fasting.  When you began to re-feed, your body is still in the process of cleansing itself.  Whatever you eat (fruit is mostly water), it goes right through your body.  Within 24-36 hours your bowels should return back to normal, meaning you should have a bowel movement at least once a day.

It has been about 3 weeks since I finished the fast as I write this.  I’ve gained back all of the lost weight, have eased my way back into running and lifting weights, and I feel great.  The biggest thing I’ve noticed is that I’ve been sleeping 1.5-2 hours less each night, and waking up feeling refreshed.  I’ve slept 8-9+ hours per night average since I’ve graduated from university, and this is the first time in my life I’ve been comfortable with less than 8 hours.  I’m curious to see how long this will last, but it has been a pleasant surprise.  Mentally I’ve felt motivated, physically I feel great, and all food tastes amazing.  You look at food in an entirely different way and have a lot more appreciation for all the amazing food in the world.

A few notes and things learned…

Below are a few notes from various podcasts, lectures, and blogs I’ve read over the last few weeks:

  • The heart and brain prefer beta hydroxybutyrate (ketones) over glucose.
  • Women have a harder time fasting – emotional response? How they metabolize fatty acids? Not sure. They hit ketosis quicker than men when fasting (less muscle to store glucose).
  • Sun exposure helps metabolism, helps raise ketone levels as a result. Yet another benefit to getting in the sun.
  • Even a 1 mmol/L increase in ketones results in 10% increase in energy to the brain.
  • It takes time for the body to get used to using ketones – permeability of ketones to cell membrane. Hence staying in ketosis longer leads to high effectiveness.
  • When we fast, the brain gets clear to help us find food. Evolutionary, this makes sense – preserve energy (feel weak), but mind is clear – enables us to stop and think about best way to find food.
  • Highly recommended to supplement at least 4-5g of sodium a day when fasting, as insulin drop causes body to release sodium. I didn’t do this on previous fasts, doing it now by pinching salt into my water (also makes it taste smoother).
  • Magnesium supplementation during a fast is also recommended. Taking magnesium right before bed is good – calms you down before sleep and leads to better sleep.
  • Nicotine gum helps hide acetone in breath, and also helps focus if writing/working on stuff.
  • If testing ketones, test mid-afternoon for ketones (3/4pm), and test same time everyday for consistency (mornings can be different as body regulates itself).
  • Fascinating to think of this whole other energy system that exists that most people never tap into.
  • Can fasting help improve vision? Helps heal myopia? Something to think about.
  • Mitochondria (powerhouse of the cell) – uses fuel like glucose and fats to use oxygen to convert to cellular energy to ATP.
  • The transition period from glucose to ketones is the hardest part. When you’re transitioning to fasting, it’s normal to feel lethargic or find yourself becoming angry more easily. Fight through it at the beginning, and you’ll find your body has adjusted and your energy levels and emotions will rebound.

That pretty much sums up water fasting as of 2017.  In the coming years I expect a lot more studies and data to backup the benefits of water fasting, and hopefully more people will do it regularly. There are a lot of links throughout the post above that are worth spending time looking into.  A few of the lectures and podcasts are 1-2 hours, but well worth your time.  If you want to learn more, I’ve included a few resources below.

Thanks for reading, and all the best on your fasting endeavors!

Other Useful Links:

The Health Benefits of Water Fasting

Each Organ Has a Unique Metabolic Profile

Dom D’Agostino on Ketosis, Fasting, and the End of Cancer

10 Day Water Fast

Ketogenic Diet Resource

Beginners Guide to Intermittent Fasting

Quantified Body 10 Day Water Fast Results

Your Brain on Ketones

The Fat-Fueled Brain

Ketosis and Your Brain Podcast

Why Fast? Brain Health

Ketosis: Advantage or Misunderstood State?

Ketosis: Metabolic Flexibility in Action


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I write for fun, I travel for fun, and I enjoy learning. I hate sugar-coating things. Understand the world in reality, not by dogma. Question everything.

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