I remembered reading about this.....In general, you'll maximize your fat loss if you wait about an hour after your workouts before eating. The exception, in my view, is when you smell ammonia. Ammonia is essentially nitrogen, and that sensation after a workout is a signal that you've raised your cortisol levels enough to trigger the breakdown of amino acids by the liver (gluconeogenesis). When the body needs energy, it metabolizes glycogen, then fat, then protein. If one isn't fast enough, it goes down the list. But if it's going to feed on protein, you want it to go after something other than muscle tissue. So if you smell ammonia, you should have a protein and carbohydrate containing supplement immediately after your workout, preferably along with a protein stimulating supplement such as L-Leucine (whey protein is about 20-25% Leucine).
I copied that from another site I read occasionally...hope it helps.