Not only does ice offer a calorie-free way to snack—it actually burns calories as your body melts it, says an expert. Gastroenterologist Dr. Brian Weiner steers patients away from fad diets, but his findings on ice have inspired him to write a free e-book of his own: The Ice Diet, the Fox News reported.

"While eating ice, you are serving two purposes," Weiner tells the Atlantic. "You are burning calories and not eating positive-calorie foods."

By Weiner's calculations, it appears to be "generally safe" for adults to eat a liter of ice a day. That one liter burns 160 calories, he argues—the number you'd burn by running a mile.

Weiner offers a number of safety guidelines: Don't, for instance, eat more than a liter a day. That could be toxic. And be careful eating ice when it's cold out.