Jason Zimdars

June 14, 2024

Fasting is a super power

I've had a long relationship with the practice of fasting—especially intermittent fasting—but at the start of 2024 I decided to try something new: two 24-hour fasts every week on Wednesdays and Fridays. Nearing the halfway point of the year I'm happy to report that the results have been great. Let's take a look.

Before we go on, don't get me wrong. It's certainly a love/hate relationship. I know it's good for me, but I rarely look forward to a fast day. But sometimes I do! After a weekend of indulging on a holiday or while traveling, it's nice to know a course correction is coming. And the negative feelings are mostly anticipatory, I rarely think about it once a fast day begins. Now back to the benefits.

Increased energy and focus

Fasting days are my best days at work. With my body free from the labor of digesting food I find myself with more time, increased (and stable) energy, and sharper focus. I simply get more done at work on fasting days. There's a surprising amount of extra time in the day when you don't break to eat and the focused energy lasts—none of that mid-afternoon post-lunch sleepiness. I'm more alert, sharp and more easily get into a flow state.

Weight loss and peace of mind

It  goes without saying that simply consuming fewer calories is going to result in weight loss. But more than that, it's a more sustainable and mentally healthy practice to fast a couple days a week rather than be on an always-on diet. On my non-fast days I just don't think much about calorie consumption and I don't have to avoid (or completely abstain from!) certain foods.


One of my favorite quotes of all time comes from the late Clayton Christensen who said (paraphrasing) it's easier to do something 100% of the time than 98%. I've applied this logic to a number of areas of my life and the key point is this: deciding is hard so if you make the decision up-front, you'll have it easier when the time arrives. On fast days I don't have to decide what to eat—it's nothing; on normal days I don't have to spend mental energy managing calories or hand wringing about this dish or that because my fast days take care of that. It makes life better.

Rest and restore

What makes fasting so effective is the idea that when your body isn't digesting food, it has the capacity to do other things. There is plenty of evidence that fasting allows your body to restore and repair itself. Cells regenerate and the body cleans out damaged cells which are often a source of disease, or increase the risk of disease. Studies are still ongoing but this easily passes the test of reasonableness. Many people in the parts of the world that are most susceptible to obesity and preventable disease rarely go a few hours without food. Three meals a day with snacks here and there forces your body to spend a lot of time and energy processing all that food. Compare this to nature, where most animals must expend tremendous energy to find, catch, or kill their food and when they can't, they basically fast. Think of the pride of lions who after making a significant kill, eats their fill and rests only to start the cycle again with finding and hunting for the next meal. It might be days before they get to eat again.

Discipline and mental health

Fasting is hard. It takes discipline to skip meals, endure the pangs of hunger, and abstain from the pleasure of eating. It feels good to do hard things. It's a notable accomplishment when you successfully complete a fast and longer term it inspires the confidence that you can do hard things and gives a sense of mastery of self. I'm a firm believer that exercise of discipline in one area of your life applies to others. A person who can master their appetites is inherently more virtuous. For example, being able to voluntarily deny yourself food builds the ability to endure discomfort when it's forced upon you. You might find yourself more likely to stick to other habits, complain less, and less prone to being offended.


Anytime I'm struggling on a fast day, my mind goes to the millions around the world for whom fasting isn't their choice. I'm grateful to have plentiful food and be in a position to choose to fast for all the reasons I've outlined and painfully aware of those who don't. 

How to do it

My Wednesday and Friday fasts are 24 hours—from dinner the night before to dinner that day. This is significantly easier and more convenient than morning to morning. For one thing, it means my personal fasting schedule doesn't disrupt family life. I'm always there to sit and eat dinner with the family and most of my fast occurs when I'm asleep and during the work/school day. It also avoids having to go to bed hungry which is tough (again, gratitude). Being busy with work helps, too. The point is not to make this a grueling as possible, so find a pattern that works for you.

Like anything else it takes practice to get good at fasting. The first several times are going to suck. The first time you go for 24 hours you might feel like you're going to die (you're not). Headaches and an irritable attitude are common. It gets easier and, in fact, you might find it to be nearly effortless after awhile. Coming off of a fast day it has often felt indulgent and unnecessary to eat three meals. You mean I get to eat again? Already?

I track my fasts using HEY Calendar's Habits feature. It helps me remember, stick with it, and see that I'm actually doing it. Here's how it looks:


But wait, it looks like you've skipped some days!

Yes! And that reminds me of one more tip. Don't be that guy. It's great that you've taken on this significant personal practice but don't burden anyone else with it. Don't be the guy who sits with only a glass of water while his family enjoys a meal. Don't skip events, or an invitation to lunch with a friend because it's a fast day. And definitely don't fast on vacation. You don't get extra points for being perfect. The good things in life are  meant to be enjoyed and, ultimately, fasting is a tool that unlocks that. It's counterintuitive but denying yourself opens you up to more joy.  

About Jason Zimdars

Product designer at 37signals working on Basecamp, HEY, and ONCE since 2009. Illustrator of It Doesn’t Have to Be Crazy at Work and the Prince Martin Epic series. You can find me on X, Instagram, LinkedIn and at jasonzimdars.com.