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2-day fasting experience

My First Two-Day Fasting Experience – 40-hours Without Food

Empty dinner plateMention to anyone you have just completed a two-day fast and the reaction is pretty much the same. Why?

What compels anyone to purposely go without food for two-days?

Rather amusingly, well for me, is that most people are surprised you are still standing after going without food for two-days! It just goes to show living in an environment where there is plenty of food, how the prospect of not eating is considered weird.

The fact is it’s really not that difficult, or at least it wasn’t for me.

I follow an intermittent fasting schedule ever since I began my 90-day fat belly challenge back in July 2019. Because I follow an 18 / 6 meal pattern, this meant I was used to not eating for mostly 18 hours each day – for 3 months.

This article is going to look at why I did a two-day fast in the place, the experience during and after, benefits of two-day fasts, and what to watch out for.

Why did I fast for 40-hours?

This seems like the most logical place to start.

I have been reading about intermittent fasting and the benefits of longer periods of fasting since following this meal timing protocol for the last 3 months.

Although I am keen to lose body fat and lose the fat belly and moobs, there are many significant benefits for extended periods of fasting. I discuss more about these in benefits of extended fasting below.

I have to admit that I was keen to see if I could even last 40 plus hours of fasting. My lifestyle is pretty comfortable since living life as an expat in Malaysia, so I want to challenge myself more and put myself into uncomfortable situations – this certainly counts as one of them, but the question is how much of a challenge would it be?

Why 40-hours?

I would like to answer with a scientific answer supporting 40-hours as the magic number.

The simple fact is I was thinking I would do a 48-hour fast but the logistics of this made it a little difficult. Aside from I wanted to make sure I suffered no side effects (see below).

As it was my first multi-day fast, I considered 40-hours long enough.

Check out why I started intermittent fasting in my articles on my fat belly challenge here.

A quick cautionary word

It goes without saying that the content contained in this post is for informational purposes only and should not be considered in any way medical or health advice.

Long periods of fasting are not for everyone!

There can be side-effects, some can be serious depending on your health. If in doubt, it’s best to check with your physician. Doing an intermittent fast may be more suitable.

If you have any pre-existing medical condition always consult your medical professional first before doing extended periods of fasting.

How to Start a 40-hour fast?

Before I started my 40-hour fast I did some research online – I know this can be dangerous considering the amount of information out there. But I only looked at trusted sources like Healthline and WebMD for fasting advice (see references below).

Getting started is really simple, as you basically avoid eating (or drinking anything with calories) for 48-hours.

What can really help with preparing for an extended fast is practicing intermittent fasting frequently. I have been an 18 / 6 intermittent fasting protocol for over 3-months now and so used to no food for 17-18 hours each and every day!

My typical intermittent fasting schedule is below.

My Intermittent Fasting Schedule

Whilst the concept is straight forward it’s worth noting what is possible to do during extended fasting. Most people don’t realize that you can actually drink zero-calorie fluids other than water, such as black tea and coffee. Importantly though you cannot add milk to your tea or coffee.

If you’re used to drinking black tea and coffee, then you won’t struggle with this. I used to be a milk tea and coffee drinker for 20 plus years but now very rarely drink milk. I found it only takes a few days to get used to drinking without milk – worth a go if you want to reduce or avoid dairy!

Importance of staying hydrated

Himalayan Pink Salt and warm waterOne important points about fasting is to ensure you drink plenty of fluids to avoid dehydration. Be aware that if you drink a lot of black tea and coffee you may need to drink even more water to compensate for their diuretic effects.

To ensure I get some electrolytes when fasting I simply put a few pinches of Himalayan rock salt into 600ml of warm water a couple of times per day. There is no need to go for any supplements or rehydrating electrolyte sachets here, this is a cheaper and easier solution.

You may notice the fancy bottle I use in the picture. This is a Joseph Joseph dot hydration tracking water bottle (you can find this on Amazon for around $16) and is useful for keeping track of how many times you finish your water. After filling the bottle, you twist the lid and a new dot appears.

One important point about fasting is to ensure you drink plenty of fluids to avoid dehydration. You will certainly want to drink more than you would normally.

The idea is you make sure to drink at least 4 bottles worth of water per day. I find that I rather use this for tracking now as I always drink plenty of fluid each day (4-6 times).

You will certainly want to drink more than you would normally. There is also the added benefit of drinking water helping you to feel full.

Benefits of Extended Fasting

With the popularity of intermittent fasting more awareness of the benefits of extended fasts has become known.

Really delving into the benefits of fasting for 24-hours or longer highlights really compelling research that is difficult to ignore. Especially if you are following an intermittent fasting meal schedule.

The most profound benefits of extended fasting come from two things, the first of which you may already be familiar with: ketosis and the cellular cleansing pathway of autophagy.

I am familiar with ketosis but autophagy was new to me – I won’t go too deep into what this is as an excellent article explaining autophagy is here. In short, the easiest definition of autophagy is;

a metabolic process during which cells disassemble and remove their dysfunctional componentssource

Scientifically Proven Fasting Benefits

  • Blood Sugar Regulation – Fasts lasting longer than 24 hours may have additional benefits for blood sugar control beyond those linked to shorter fasts (source)
  • Weight Loss (but not necessarily all fat loss) – A 48-hour fast once or twice per month will reduce your monthly calorie intake by up to 8,000 calories per month, which can promote weight loss
  • Inflammation Reduction – Fasting for more than 24 hours may lower inflammation by reducing oxidative stress in your body’s cells (source)
  • Slow Aging – Studies indicate that 48-hour fasting can improve cellular repair more than other fasting methods (source)

My Experience of 40 hours without food

I found it surprisingly easy actually.

I was hesitant to try for this length of time having only completed one 24-hour fast last month.

The first 18-hours was the same as any other day for me, as I have been doing this for the last three months. Going past 18-hours with no food and I started to suffer from a headache, but this may be because my coffee consumption was higher than normal for that morning (5 coffees instead of the usual 3).

To help alleviate the headaches I drank lots more water, which kept me in and out of the toilet all afternoon.

The next morning, I felt amazing. No hunger pains instead I felt alert and focused, ready for the day ahead. It was a great feeling.

The hunger pains started after 20 hours and my stomach was making some interesting noises in the evening. My feelings of hunger were thankfully short-lived though and just before heading to bed stopped.

The thing with hunger is it’s never constant and comes and goes. And for me, as long as I don’t think about it too much, the feeling goes away.

I was tired of going to bed and so slept really well for 7-hours with waking only once for the toilet.

The next morning, I felt amazing.

No hunger pains instead I felt alert and focused, ready for the day ahead. It was a great feeling.

After dropping kids off to school, I did my short walk to a local coffee shop along the promenade near to me in the blazing hot sun feeling really alive.

Working for a few hours in the morning and having a couple of black coffees I easily managed up to lunch-time.

Although it’s tempting to go straight into the main meal the advice after fasting is to ease into eating again. So, I grabbed 5-6 brazil nuts and avocado as a light snack before going to school to pick up my kids.

Three-hours I ate my main meal, which consisted of salmon, vegetables, and mash potatoes. I experienced no indigestion issues, only some tiredness in the evening and so went to bed at a decent time.

The next-door I did feel a little tired even though I managed to get a solid 7 hours 30 minutes sleeping – all tracked using my Oura ring.

The tiredness could be because of having poor sleep a few days before the two-day fasting or to the fasting itself, I cannot be 100% sure. Most likely it’s a combination of the two.

Did I lose weight doing an extended fast?

I am very keen to shed some fat since gaining over 6kg in 18-months and really feeling flabby. I am realistic though and fasting for two-days is not going to massively move the weight scales needle.

That said, I lost in total 1.2kg (2.6 lbs) in just 48 hours. Not all the weight loss is body fat though, as a large portion will be down to the water.

I lost in total 1.2kg (2.6 lbs) in just 48 hours. Not all the weight loss is body fat though, as a large portion will be down to water.

Although I was very well hydrated, my carbohydrate stores would have been depleted, and considering for each gram of carbohydrate there are 3 grams of water stored – this can soon add up.

There is a superb article on glycogen (the stored form of carbohydrate) and water retention in this article by Justin Owings.

In summary, the quickest weight loss on a diet is water weight.

Glycogen is stored in the liver, muscles, and fat cells in a hydrated form (three to four parts water) associated with potassium (0.45 mmol K/g glycogen). . . .
Glycogen losses or gains are reported to be associated with an additional three to four parts water so that as much as 5 kg weight change might not be associated with any fat loss.


You can see that glycogen stores can have a profound effect on body weight!

Do you Experience Side Effects from Extended Fasting?

Fasting for a long period of time can cause some minor side effects. From my research, it seems it’s typical to experience some side effects although most are relatively mild and not cause for concern.

It should go without saying of course, that if you experience extreme side effects then you stop immediately and seek help.

I expected to feel hunger pains, and these were mostly present between the hours of 18-24 into the fast. The thing is these are not constant hunger pains as they come and go.

I was concerned this would prevent me from sleeping, but fortunately, I was so tired from not sleeping well the night before, that I fell straight to sleep.

Common Fasting Side Effects

  • Hunger and Dizziness – Side effects such as insomnia, hunger, fatigue and dizziness are common if following 48-hour fasting
  • Exhaustion – After 24 hours you run low on stored carbohydrates and so fat becomes the main fuel source

How Often Will I do a 48-hour fast?

Fasting for two-days is not something you do every week, it’s more common to do it once or possibly twice per month.

I am going to do a weekly 24-hour fast that starts on Sunday night until Monday evening. This is the most suitable time for me as weekends would be harder being with my family for mealtimes.

On Monday though, with my intermittent fasting schedule of 18 hours fast and 6-hour feeding time, I can simply go without lunch and join my family for Monday dinner. This will be a full 24-hours without food.

Final Thoughts on Two-day Fasting

I found that if you ignored the fact you haven’t eaten for some time you don’t get caught up in the obsession with food – and more importantly the fact you HAVEN’T eaten and will be hungry!

As I didn’t need to think about food, I had more time in the day as there is no time planning your meal and then actually eating it. It can feel like a long day though, as meals naturally break up your day.

As a substitute for food, I found I drank more coffee than usual during the first 18 hours of my fast. This may have contributed to my afternoon headache!

Overall my experience was really positive, and I would not hesitate to do it again and make this part of my monthly routine.

Adam Author

About the LifeHacker Guy

Hi, I'm Adam the founder of the LifeHacker Guy.

I have a First Class Honours degree in Sports Science from Brighton University, specialising in exercise physiology and nutrition. In my youth I was a competitive Triathlete and long-distance runner placing top 10 in most triathlon races I completed.

Since suffering from Chronic Fatigue Syndrome, I moved into web development, after a couple of years I then moved onto developing a number of online businesses. I've recently taken a sabbatical and I'm now looking to make big changes in my life, hopefully this may resonate with you - join me in my journey!

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