A CEO who swapped the bulk of his food for Silicon Valley's favorite futuristic meal replacement drink explains how it makes him more productive

Or rather, drinking.

Since September 2016, Shashoua, who is the 34-year-old CEO and founder of Kiwi for Gmail, has consumed the meal-replacement drink Soylent almost exclusively.

"It's massively changed my life as a CEO," Shashoua told Business Insider.

As Business Insider's Kate Taylor has reported, the first version of Soylent was invented in 2013 by founder and CEO Rob Rhinehart. For the past few years, it's been popular within Silicon Valley and the tech industry, though Taylor wrote that the company has recently tried to appeal to a wider audience.

Shashoua said he typically drinks between four and four-and-a-half Soylent drinks every day. Each drink has 400 calories, so that adds up to between 1600 and 1800 calories.

For one out of every six meals, Shashoua said he has a hearty dish, like a steak. He's hoping that someone will develop a more substantive meal-replacement drink so that eventually, he won't have to eat any solid food at all.

The switch to a mostly liquid diet wasn't motivated by health concerns — instead, it was a kind of extreme productivity hack. Before he started, Shashoua said he would spend unnecessary time and energy figuring out what to eat and was getting tired of the restaurants nearby.

He'd also previously experimented with unconventional diets, such as eating the same Subway sandwich every day.

With his current diet, "I was looking for any edge that I could get," Shashoua said, "in terms of basically cheating in some way to get more productivity."

Shashoua said he consulted a doctor before starting the liquid diet, who told him, "I've never seen someone do this before."

Still, Shashoua said, the doctor "didn't tell me no."

Since September, Shashoua said he's been getting blood tests specifically to check his A1C levels, which reflect your average blood sugar levels. He was concerned that the liquid diet might cause his blood sugar to spike; it hasn't.

"If you cut out an hour and a half of your schedule" that you'd normally devote to eating, Shashoua said, "you have more time for other healthy things," like exercise. He said he typically exercises on the days he eats steak.

Shashoua cited Mark Zuckerberg and Barack Obama, both notorious for wearing nearly the exact same outfit every day and explaining that it conserves their decision-making energy.

"The more you can cut out the less meaningful decisions" — in his case, what to eat for lunch — "and save energy for things that are more important, that's more helpful," Shashoua said.

In fact, research on so-called "ego depletion" is mixed. Recent studies have been unable to replicate the original finding that our willpower is limited.

Shashoua added that it helps to get hungry at the same time every day, and to be able to satiate his hunger in the five-minute space between meetings. He doesn't experience the post-lunch crash that he would when he was eating solid food regularly.

He hasn't yet gotten sick of Soylent's taste.

Shashoua said he's tried to convince the rest of his team at Kiwi to try a liquid diet — so far, to no avail.

"One of the hardest things for people to get over is the enjoyment of food," he said. "So it takes a certain intensity."