According to Dr. Brian C Weiner, a gastroenterologist and Assistant Professor at the Robert Wood Johnson Medical School in New Jersey, "...It turns out that when you eat ice and melt it, that takes energy. Ultimately what this leads to is that ice is a negative calorie food."
The idea of using ice as a dietary aid came when the Weiner wanted to lose some weight. He had given up ice cream, but was still eating 100 calorie Italian ice cups. As it turns out, he eventually realized, it takes energy to heat up the ice when it goes into a persons body. So, in terms of overall calories, an ice cup should only account for about 76 calories, when all is said and done.
So far he's lost more than 50 pounds on the diet. He's been eating shaved ice with flavorings, but it's important to know that he's also eating healthily otherwise and exercising regularly.
While it's a pretty straight forward diet, Weiner notes that it's important to not eat too much. He recommends sticking to one liter max. Oh and that chewing ice cubes is a bad idea, because it can ruin enamel on teeth. Shaved ice and popsicles work best.