top of page

From Eating 4 Meals a Day to Fasting 20 Hours

How fasting 20 hours per day changed my life

Fasting is one of the oldest practices of mankind and it exists in almost all civilizations in one form or another. Its use originates from V Century b.C. when it was used by Hippocrates for therapeutic purposes and since then it has been a part of spiritual and wellness practice. However, it was only after Yoshinori Ohsumi was awarded the 2016 Nobel Prize in Physiology for “discoveries of the mechanisms for autophagy” that fasting really started to attract more and more people. Ohsumi identified fasting as one of the ways to trigger autophagy (natural, regulated mechanism of the cell that removes unnecessary or dysfunctional components) motivating all health-conscious people to embark on their fasting journeys.

There are a lot of different fasting practices that go from a 16 hour daily fast to week-long fasting or even more for the most courageous. While the benefits of fasting are now widely demonstrated by science, the question of what “dosage” is optimal remains disputed. As Dr. Peter Attia explains it, fasting may be the most powerful “drug” out there, but the question of its optimal dosage remains widely unclear. The most beneficial fasting protocol for health purposes is still to be determined, which is why self-experimenting with fasting makes a lot of sense. And that’s what I decided to do!

How did I get into this?

I remember my friends talking about a fasting retreat a few years ago. A simple concept: only water for an entire week… At that time I thought it was another weird practice for people in a never-ending quest for the latest trend to try. But I started learning about it as I stumbled more often upon the scientific evidence that showed how much fasting promoted good health.

I always had a tendency to put on weight easily. Hungry or not, when it was time to eat I would have a big meal and I would often end up being in a caloric surplus. Besides that, I started noticing that I could go without eating for increasing amounts of time between meals. So I thought that, in addition to promoting health, fasting could help me control my nutrition by removing the excess food without it being too much of a constraint.

My first steps into fasting

I started my fasting journey with the classic 16 hours daily fast. I have never been a breakfast person, so it was not very hard. I would typically have my meals between 1 pm and 9 pm. I noticed a better focus quality during the morning. I found that fasting helped me control myself. We all have that colleague who often brings a sugar-loaded breakfast for the team… When you fast you can resist it much easier. You are not going to take “just a bite” that ends up with you eating three pastries. Fasting eases the constant decision-making process you go through every day. As Nir Eyal, author of the book “Indistractable” put it: « The antidote to impulsiveness is forethought ». By having fewer meals, you also have fewer decisions to make regarding what you are going to eat. You have a simple plan that eliminates a lot of decision fatigue, and a lot of unhealthy snacks.

For me, fasting was perfect: fewer problems, improved focus, and a way to keep my nutrition on point. It became my new eating habit for the next two years. I was not thinking about it anymore until a few weeks ago when I had to spend the entire day at an event. I didn’t bring lunch with me and the food available there was not appealing. I decided to skip lunch. After a coffee, some water and a few minutes, the hunger disappeared. I got back home at around 6 pm and had my first meal. This had me thinking: I was very productive and the hunger was more or less easy to manage. So I repeated the experiment, only this time I increased my daily fast in order to get more benefits from fasting without adding discomfort.

My experience with the 20h daily fast

I increased fasting going from 16 hours to 20 hours without eating. At first, I wasn’t sure if it was going to be sustainable in the long term. I like trying new things regarding my eating habits and nutrition, but I always make sure that it wouldn’t affect negatively other aspects of my life. I started this second fasting experiment 6 weeks ago. Now, I can safely draw some conclusions from this experience.

For me, fasting 20 hours daily only increased the benefits of the 16 hours fast without bringing any bad side. The decision-making parameter is even easier to manage. Not having to buy lunch anymore meant no more hungry bad decision-making. Fasting afternoon means being able to easily resist the birthday cake at work. And on top of that, one major advantage of this protocol is the appreciable disappearance of the famous afternoon slump. Lunch, like every other meal, is associated with a period of digestion that very often translates into feeling sluggish or needing to take a nap.

I found out that the lunch break is actually a great time to focus and do your work without being interrupted. I also like taking a walk to reset my energy for the afternoon. I always had a hard time getting back to work after lunch. The first hours of the afternoon were rarely productive. Now it’s the opposite. You might now think: is it hard to go 20 hours without eating? In my personal experience, it was challenging during the first couple of days but water and some coffee helped me suppress hunger. After a few days, I developed a better resistance to hunger and it became easier.

But, it’s not for everyone

While fasting 20 hours, I would typically have two meals. When you do a 20h fast you need to fit all your daily calories in a 4 hours window which can be challenging. Exceeding your caloric needs is even harder. So, if you’re struggling to eat enough or if you’re not used to eating a lot of food per meal, following this protocol might be hard for you. But for everyone that usually tends to overeat, this practice is great.

Fasting can also compromise your social life. Meals are inherently a social moment during which people gather. In many social groups, it’s almost the only special time when people have to make the effort to be together. Adopting a 20h daily fast would typically leave you with only one potential shared meal. For me, dinner has always been the only important “social meal” of the day so I don’t feel that I am missing out on anything while fasting 20 hours. However, if lunch is for you a great social moment, you don’t necessarily want to miss out on those.

Exercising regularly and intensely can also be a challenge if you are fasting. Finding the right timing to train can be tricky: whether you are not going to eat for hours after training or you are going to train after long hours of fasting. Pairing fasting and training requires a thoughtful process and a reliable understanding of your body. Personally I don’t mind training while fasting as I made it a new habit, but it can be harder for some people. However, I think that to reach your peak performance, the timing of exercise and feeding is crucial. I don’t view my approach as optimal regarding this. For example, fasting 16 hours on training days and 20 hours on non-training days could be an improvement. I might experience that soon!

Side effects

I didn’t experience any major side effects. However, I tend to feel cold during the afternoon, and after checking, it seems that I am not the only one to have this side effect. I also noticed that my skin is more greasy during the fast, but I have yet to figure out if it comes from the increased fasting window.

Next steps

For the moment I am very happy with the 20:4 protocol. I am going to stick with it for a while. I don’t think extending it to 22:2 makes a lot of sense because eating all the daily calories in 2 hours is really not enjoyable.

By getting more into the science of fasting with the Zero App (that I highly recommend to track your fasting!) or with the work of Peter Attia, I realized much of the health benefits occur after 72h of water fasting. I already did a three-day water fast in July and I definitely want to be experimenting more with longer fasts now.


If you'd like to receive future articles by email, and weekly updates where I share the most valuable things I've learned in the week, subscribe to my newsletter!

bottom of page