CICO is absolutely true, that's a fact. All you have to do is look at the basic physics. If you reduce the mass of the Earth by 50% (without decreasing your distance from Earths center, a common trap people fall into when they're trying to lose weight), you will lose 50% of your weight.

Fad diets and "body mass" are, excuse my harsh language, B.S. Yes they can contribute to weight loss but they are going to let you lose 10 or 15 pounds tops. Reducing the weight of the Earth, on the other hand, can get you to lose essentially any amount of weight.