(THE GUARDIAN) — The last time any food passed Phil Libin’s lips was a day ago, when he ate yakitori at a restaurant in San Francisco’s Mission district. He’ll next eat in three days time on Thursday evening, when he has a reservation at one of the fanciest sushi restaurants in town. In the intervening four days it’s just water, coffee and black tea.

Over the last eight months the former CEO of Evernote and current CEO of AI studio All Turtles has shunned food for stretches of between two and eight days, interspersed with similar periods of eating. He’s lost almost 90lbs and describes getting into fasting as “transformative”.

“There’s a mild euphoria. I’m in a much better mood, my focus is better, and there’s a constant supply of energy. I just feel a lot healthier. It’s helping me be a better CEO,” he said over a cup of black coffee – one of many that day – at All Turtles’ Soma office. “Getting into fasting is definitely one of the top two or three most important things I’ve done in my life.”

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