A Facebook executive says fasting for 15 hours a day changed his life - here's his daily routine

In 2014, Dan Zigmond, director of analytics at Facebook, lost more than 20 pounds in less than a year. He didn't track steps or count calories. Instead, Zigmond gave up eating for 15 hours a day.

"I don't think about it as 'fasting,' per se. There's a period of time where I eat, and there's a period of time when I don't," Zigmond told Business Insider. "Life is all about balance."

Zigmond, a father and a practicing Buddhist, subscribes to a trending diet called intermittent fasting, which involves going without food for anywhere from 14 hours to several days.

The science behind intermittent fasting is spotty. Most studies use rodents and fruit flies as test subjects, rather than primates and people, as Scientific American reports. Still, it's catching on among startup workers looking for simple solutions to slim down and sharpen their minds.

A paper from the Salk Institute for Biological Studies turned Zigmond onto intermittent fasting. It suggested that when you eat might matter as much as what you eat. Mice with feedings restricted to certain hours of the day became thinner than mice who were fed whenever, according to the study. Zigmond was reminded of his time living in a Buddhist temple in Thailand, where the monks followed a similar routine, and decided to give it a go.

Zigmond - who counts Microsoft, Google, and YouTube among his past employers - eats during a nine-hour window each day.

Most days begin the same. He wakes around 6 a.m. and takes a quick run around the neighborhood while listening to Kanye West. After getting his kids ready for school and guzzling a large cup of green tea, he arrives at Facebook's Menlo Park, California, campus.

His first meal comes at 9 a.m. Zigmond grabs a bowl of oatmeal topped with Greek yogurt from Facebook's cafeteria, and he sometimes adds a handful of granola, blueberries, or bananas.

"I try to take half an hour for breakfast, without doing any work," Zigmond said.

Through a morning of meetings and writing at his desk, Zigmond tries to stay hydrated by drinking an unsweetened iced tea. When lunch rolls around at noon, he leaves work for a full hour and finds a lunch-buddy with whom he can talk about "non-work" stuff.

"I'm very flexible about what I eat at lunch - there's no rules at all," Zigmond said. "Yesterday I had pizza. My favorite is Indian food, but I have to bike over to the other campus for that, so only do that maybe once a week."

In the afternoon, he conducts one-on-one meetings with members of his team, preferably outside. Zigmond walks over 15,000 steps, about seven miles, on a typical work day.

A ginger shot from a nearby juice bar gives him a 3 p.m. boost.

At 5:30, Zigmond gets dinner from the company's extensive cafeteria. Dinner tends to be his smallest meal, since he eats so heartily at lunchtime.

"Often I'll just make a sandwich, which is what I did yesterday. Other times I'll grab a bowl of rice and curry from the cafeteria," he said.

He leaves the office around 7 p.m. to run errands or pick up his daughter from dance. A cup of herbal tea tops off the day. ("I drink a lot of tea.") Lights out at 10 p.m.

Zigmond, who co-authored a book, "Buddha's Diet: The Ancient Art of Losing Weight Without Losing Your Mind," has no plans to change his diet - or lack thereof - anytime soon.