I Fasted 18 Hours a Day for 7 Days

Pete Ross

Photo by DESIGNECOLOGIST on Unsplash

I’ve been thinking about doing some fasting for quite a while. I’m an athlete and very healthy, but as a 40 year old I can’t ignore the mounting evidence that going without food on a regular basis is very good for you and has a lot of bang for buck when it comes to anti-ageing. Having found myself at home and off work due to heart issues, I figured now was the perfect time to give it a shot.

It was an interesting experience.

The experiment

There were several reasons I wanted to do this on a regular basis — that being once per calendar quarter. I live a healthy lifestyle and am pretty lean, but with my enjoyment of food and a couple of drinks, there’s a good chance I’ll have to work harder to control my weight as I get older. I figured 7 days, once per quarter eating only 1–2 meals would do the following:

  • Give me the anti-ageing benefits of fasting, and
  • Trim me down by 1–2 kilograms

The reason I settled on this is for a few reasons, the main one of which is that it’s achievable and not too difficult. It doesn’t take a bunch of prep and planning, and I’m not going too long without food. It’s not a huge imposition on my life either, which is important considering I’m a very busy person. Finally, doing this four times a year as something of a “reset” just makes sense. 

So, how did it go? I found a few interesting things…

I got the dreaded “keto breath”

One of the things fasting does — assuming your body is adapted to it, is go into ketosis. That means your body burns fat as its primary fuel source, which is awesome if you’re trying to lose some weight but comes with a nasty little side effect: your breath stinks. That’s because you’re expelling some of the metabolic after effects of ketosis through your breath.

I didn’t even realise it until my wife said something. I did the breathe into your hand and sniff it test, and man, it was disgusting. To caveat, I have pretty excellent oral hygiene and bad breath isn’t something that I hear about. My wife isn’t backwards about letting me know either. Apparently you can mitigate the effects by drinking more water, chewing gum or mouthwash. 

Not a big issue, considering I only plan on doing this for 7 days at a time.

You can get constipated

The thing about fasting is that it’s really easy not to drink enough. I generally have a couple of cups of coffee in the morning and I’m quite regular. I’m not having my usual afternoon protein smoothie though, so there’s about 600ml of water gone. Apparently with fasting and possibly ketosis, you just have to drink more water as a rule. 

Add to that the fact that you obviously aren’t eating as much, which means you don’t need to go as often, which I found makes it harder to go.

You’re nowhere near as hungry as you think you’ll be

I freaking LOVE food. By any measure you could call me a foodie, because I’m always looking for something new to try and very little is off limits for me. I even look forward to breakfast every day, because I alternate between muesli with berries and yoghurt, and scrambled eggs. Knowing that I was going to wake up and not eat that delicious breakfast was tough the first couple of days.

But I never really felt hungry.

You’re always going to get that small pang first thing in the morning, because that’s your body flooding with cortisol, waking you up and making you want to eat. As I instead have a coffee, I’m over that hump pretty quickly and easily. From there it’s usually only another 5 hours or so until I get to eat. Only once did I really feel hungry, and that was at hour 17.

You can get by on a lot less

When you’ve fasted for 18 hours, your stomach naturally shrinks significantly, so when you break your fast with a meal it’s only natural that you feel satisfied much more quickly. This actually keeps on going. Now, if I ate a fairly small meal I’d be hungry again after a few hours, but if I ate a decently large meal, I wouldn’t be hungry again until about 5 hours later, which would be my second meal in the 6 hour window.

A couple of times, I wasn’t even hungry then. I honestly felt like I could go on just the one large meal for the day. I realised though that if I did go without that second meal, I’d probably be ravenous the next morning. I don’t know for sure though, and that’s something I’ll definitely test out the next time.

It’s also worth noting that because this was a fairly sudden decision, I wasn’t completely prepared. My initial plan was to do it keto — lots of protein and fat, no carbs, which presumably would have had me feeling fuller for longer. I have a feeling if I did do it in this manner, I could comfortably go on one meal a day.

I look a bit leaner

Again, because the timing of this wasn’t planned, there are no before and after photos, no weighing and no measurements. I will say that I definitely look a bit leaner and I might have lost around a kilo. That’s not bad when you factor in a couple of things:

  • As an athlete, I’m already quite lean (not shredded like a steroid user though)
  • During this period I was very inactive, as I was resting while I waited for my cardiologist appointment. Had I kept up my normal activity, I’d guess I would have lost 2–3kg.
  • I didn’t eat quite as healthy as I normally would have planned for this activity

I’d guess if you’ve got a few too many kilos on you and you keep your activity the same, you’ll definitely lose a few.

Energy levels

Surprisingly, I didn’t feel any change to my energy levels. That’s probably because I’ve got my diet pretty dialed in normally, I get good sleep and I know my body really well. I hear a lot of people find themselves much more energetic when they fast, which could be due to the fact that they don’t have the usual crap in their body. 

I’d wager the fact I eat a low carbohydrate diet — by general population standards anyway, also has a hand in this. I can slip into ketosis fairly easily so I’m quite well fat adapted and don’t suffer from any kind of brain fog or 3pm tiredness like a lot of others. 

The test for next time is going to come with my activity. I normally train 5 days a week and get 10,000 steps a day. For the last week, I’ve done nothing and my step count has maxed out at 5,000. There’s a chance I’m going to get tired and pissed off, but there’s also the possibility that I’ll just eat a little bit more and it will be much the same.

So what will I change for next time?

Next time, I’ll obviously have it planned in advance when I’m going to do it and what I want to eat. I’ll be starting on a Monday so the first 5 days will be while I’m working and training as usual, so I’ll have everything made in advance. It will also be protein and fat only, for maximum effectiveness, at least until the Friday or Saturday when I would normally indulge in eating out.

That’s really about it.

One of the more major changes I’ll be making is with my regular eating. As I said, I have no intention of fasting every day, but I could definitely eat a little less. As I work from home, it’s not a big deal to move breakfast back a couple of hours. What that means is that I’ll go 14 hours between dinner and breakfast, which will push lunch a bit later. That means there’s no need for an afternoon protein smoothie anymore.

As I’m not pushing hard on the weights these days, that extra bit of protein is probably unnecessary. As usual I’ll monitor it though, because maybe I’ll see a decline in body composition, energy levels and recovery. I suspect not though.

Final thoughts

I’m definitely happy that my instincts on this were proven right. It wasn’t too uncomfortable at all and there were actually a lot of benefits. Measuring the effectiveness of the anti-ageing / autophagy part of things is pretty much impossible, but from everything I’ve read, I’m definitely getting at least some of the benefits.

In future I might look at doing shorter periods of complete fasting (like maybe a 2 day fast once a quarter) or possibly trying one meal a day, but we’ll see how we go. For now, I feel like this is a solid entry level way of getting all the benefits of fasting without going too deep into it. 

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I write about career, performance, psychology, self development and business humour. I'm an author, former national competitor in judo and strongman and a former military instructor.


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