Once a week I skip food for 36 hours. I finish my last meal around 8 p.m. on Monday night, have nothing but water and sometimes black tea on Tuesday, and break my fast on Wednesday morning around 8 a.m. If that sounds nuts and a little dangerous to you, I get it. That was my own reaction when I first experimented with fasting about a year and a half ago. But since then, I haven’t looked back.

I didn’t start fasting to lose weight. In fact, as a naturally lean guy with a fast metabolism, skipping meals sounded like a recipe for shriveling away both physically and mentally. But two things happened toward the end of 2015: Dr. Sandrine Thuret of King’s College pointed me to her TED talk about boosting the growth of new brain cells by fasting, and a colleague of mine didn’t eat on certain work days because he claimed that it would extend his lifespan. This got my wheels turning to understand the biology behind why this could work and to try it for myself.

The first time I fasted for 36 hours, it was horrible. Through my entire life, any inkling of hunger triggered an instant reaction to grab a snack. It took two weeks to break that instinct. But by the third week, my body started adapting into better using my own fat reserves. Instead of shriveling away, four things happened.

I learned the difference between bored hunger and true hunger. This became especially salient when I did a seven-day extended fast recently. Still able to lift heavy at the gym and have a productive work week, I saw that my body had incredible energy reserves even when I wasn’t constantly eating. It didn’t hurt that breaking the fast was one of the most pleasurable and happy moments. That sheer happiness crystallized for me that eating is fun; our bodies literally produce happy transmitters when we eat. But because we eat all the time, we’re desensitized to the hedonism of eating, and fasting rekindled that feeling. I shunned junk food. After I trained my mind to avoid eating for extended periods, the discipline around my consumption extended to food choice. If I have a constricted number of meals or times I eat, I better damn well make them great meals. It’s now easy for me to skip crappy airport food and hold out for the good stuff. Fasted days became my most productive days. I subjectively feel a boosted state and focus as my body compensates to produce ketones, cortisol, and other stimulatory biomolecules. When I fast, I imagine myself as a “hunter monk” with Zen-like flow being applied and directed to whatever task I have at hand — which you need to have since you aren’t taking any breaks for a slice of pizza. I got a leaner-looking body. Over three months of rigorously tracking my body composition through special DXA body scans, I went from 17.1-percent body fat to 16-percent body fat and gained 4.5 pounds of lean muscle mass. In fact, an extended fast is one of the most reliable ways to naturally elevate human growth hormone, a key factor to retain and build lean muscle.

While this was my fasting experience and it works for me, there’s plenty of skepticism associated with the practice you should consider before jumping in. Don’t fast if you’re underweight or malnourished. When you break a fast, eat plenty of good, healthy food, since the focus of fasting is changing the timing of eating, not the reduction of calories. Lastly, remember that a lot of your daily water intake comes from food. So if you aren’t eating, make sure you’re staying hydrated. Fasting can be illuminating — but you have to do it safely.

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