You're going to have to be a lot more specific. What do you mean by fasting? Intermittent fasting? Extended fasting? How long? Obviously, if you go without intake of calories, you will lose weight, but there's a reason anorexia is considered an eating disorder, you can do yourself great harm.

If you're talking about intermittent fasting, which is basically just confining your eating to certain times of the day, I know people who swear by it, and I doubt you can do yourself any harm. If you're talking about not eating for several days at a time, please don't try this. More likely, you'll lose a lot of muscle tissue, and if you carry it to an extreme, one of those muscles is the heart.