Originally Posted by redgoober4life
No, it is never a good idea.
When you deprive your body and then do cardio, you'll actually be using energy derived from lean muscle instead of energy from fat. So of course you'll lose weight, but is it the weight you want to lose?
And this isn't to say you need a ton in you, but creating highs and lows in blood sugar levels is not healthy for anybody.
When you do cardio with an empty stomach, your body begins to convert both muscle and fat into energy. Both get consumed. If you have plenty of fat, though, your body is able to rebuild your muscles and concentrate mostly on getting rid of the fat. If you're body is getting enough amounts of the proper nutrients (on a longer term scale than just daily or before the exercise), then muscle consumption will be minimized and fat burn will be maximized.
The best way to burn fat, for guys, is to build lean muscle and eat 6 smaller meals a day. Lean muscle consumes fat, and the 6 smaller meals keep your metabolism going at a faster rate. Cardio's inefficient compared to this, but Cardio's easier for most people too...