On the streets of Silicon Valley, free food flows like water. The cupboards filled to their brim with snacks, the fridges overflowing with with LaCroix, the catered lunches and on-site chefs.

That doesn't matter much to some Silicon Valley startups and executives. Because they're not partaking in these fruits. They say fasting is their secret to increased productivity and focus.

Facebook director of analytics Dan Zigmond told Business Insider he fasts for 15 hours a day. The eight-person team at startup Nootrobox doesn't eat from Monday night to Wednesday morning, Fortune reported. They've even created a group -- WeFast -- and invite others to partake in their weekly 36-hour fast and join them for a fast-breaking meal every Wednesday. You can request join their Slack channel, currently 1,184 members strong.

It's called intermittent fasting, and those who swear by the practice draw from research that suggests when you eat may weigh more heavily into your health than what you eat. A study found mice that ate during certain times had lower cholesterol and more muscle than mice that ate whenever they pleased. It's worth noting mice were the subjects of this time-restricted feeding diet study, not people.

Even so, the intermittent fasters of Silicon Valley swear by it. Nootrobox CEO Geoffrey Woo compares the results of fasting to what monks must experience. "Your mind is disconnected from the body, less constrained," he told Fortune. "There's clarity, calmness, and productivity."

Facebook executive Dan Zigmond doesn't eat between 6 p.m. and 9 a.m. He says intermittent fasting not only helped him lose weight, but also gives him more control of his eating habits. His jam-packed day often means he's eating on the go and can't always control what he eats. It's easier to control the times he eats. Zigmond co-written a soon-to-be-released book about it called Buddha's Diet: The Ancient Art of Losing Weight Without Losing Your Mind. Here's a summary of what it covers:

It's not what you eat that's important, but when you eat. You don't need to follow the latest fads or give up your favorite foods. You just have to remember a few guidelines that Buddha provided--guidelines that, believe it or not, will help you lose weight, feel better, and stop obsessing about food. Sure, Buddha lived before the age of doughnuts and French fries, but his wisdom and teachings endure, providing us with a sane, mindful approach to achieving optimum health.

For the entire startup that fasts together, there's also the benefit of team building. Everyone's fasting at the same time and providing each other support. So what if someone decides they don't want to participate in the group team-building fasting activity? At least they'll have first pick of the office kitchen's best snacks. Because no one else is touching them.