The time for your stomach to be "empty" varies greatly, depending on your own body's rate of digestion, as well as what you ate, hydration levels, etc.

But, the standard answer is 2.5 hours after a meal.

However, from personal experience, I find that I have much better workouts when I have the proper fuel in (I am speaking of resiastamce training here ... everyone knows how I feel about empty stomach cardio)

I tried the GH release thing (which has been preached for years by some in the bodybuilding community ... I thing Dr. Fred Hatfield was big on it, but I may be off on that one ...) My workouts were always lackluster, and I found it hard to substantiate any gains made by GH release due to training that way.

I feel better having a protein shake 45 mins. prior to my weight training, and another right after weight training ... then a meal 30 mins to 1 hour later. My muscles feel "fuller" and it enhances recovery.

I HATE feeling hungry while working out.

But everyone is different, give it a shot and let us know how it goes.