No downsides to intermittent fasting, science says. What to know about this popular practice

From wellness circles to religious observances, fasting is practiced by people from all walks of life and for a variety of reasons.

In fact, a recent U.S. survey showed that 10% of Americans say they engage in some kind of fasting regimen. That's more than other popular eating practices like vegetarian (3%), Mediterranean-style (5%) and Keto (7%).

But are there actual health benefits to controlled calorie restriction? And how do people know if they should try fasting?

"There doesn't seem to be any downside to intermittent fasting or ... restricting any eating you do to a certain number of hours per day," National Geographic contributing writer Fran Smith told ABC OTV.

Smith explored the science behind fasting for the publication's new "Mind, Body, Wonder" series.

"You don't need to eat three times a day. Or every three hours. No. We are not babies. We don't need to grow," Tzipi Strauss, a physician who is establishing a clinical center for healthy longevity at Israel's Sheba Medical Centre, told Smith.

Decades of research show the upsides of fasting, Smith found. It's good for controlling blood sugar, promoting heart health, reducing excess weight, protecting against chronic disease and possibly delaying cognitive decline.

It may even help reverse the effects of aging.

"[Intermittent fasting] promotes this cellular process called autophagy, which is a fancy way of saying self-eating. Your cells self-devour their own debris, and that allows the cells to replenish themselves with really functional components and function much better," Smith said.

Smith clarified that this research does not extend to days-long fasting, which can cause muscle loss and other problems.

But short-term food-free intervals can work for almost everyone, even those with physically demanding lifestyles. One study showed that San Diego firefighters working during California's grueling fire season responded well when a fasting regimen was introduced.

"There were no issues with performance, and, in fact, the eating regimen showed all kinds of benefits ... They really showed improvements in their heart function and in their sugar levels," Smith said.

From skipping breakfast daily to changing eating patterns weekly, researchers have experimented with a wide variety of fasting protocols -- even on themselves. The ideal ratio of how much to eat and when may exist, but science has yet to figure out what that is.

"One of the really interesting things to me in reporting this is how many scientists in the aging and longevity space actually do fasting ... They're persuaded by the evidence," Smith said.

The bottom line: find out what's right for you.

"Any fasting protocol is better than no fasting protocol," Smith said.

In her reporting, Smith found that one researcher even designed a diet that tricks your body into thinking it's fasting. Read more on NatGeo.com.

The Walt Disney Co. is the parent company of National Geographic Partners and this ABC station.