Celticmusl saidCardio in the morning before breakfast on an empty stomach, over 20 minutes in duration, has been proven in clinical studies to burn more body fat than cardio after eating. I'm not sure if the study had anything to do with strength or resistance training.
The current rule of logic for strength training is to eat a small meal before a workout(pre-workout protein drink perhaps) AND after a workout(post workout protein drink containing a good amount of carbs). This is what most of the Personal Trainers that I know will tell me.
I actually eat the biggest meal of the day before I work out, because if I haven't eaten anything I feel kind of sick to my stomach during weight training. Perhaps it breaks down or dilutes the lactic acid build up for me? Who knows.... But I get chastised by the PT's. I don't bother with a post workout meal because I usually don't feel hungry and my digestive system is still working on the pre-workout meal.
This is the closest answer here.
Be mindful that if your blood sugar gets to low, you'll go into famine mode, and burn protein, and WILL NOT get the results you might want in terms of training.
For weight training, having your blood sugar up during training is critical to performance. Carbing up post workout along with protein is critical during the golden hour.
Some folks sabotage their training through inadequate calories and training with low blood sugar.
There's an easy test: Ketostix. You shouldn't be going into ketosis when trianing..pretty much EVER.
Calories before, and after, working out, are CRITICAL to your excercise performance and recovery.
Early morning HIIT can be done on a empty stomach, but, you SHOULD eat something to make sure that you have adequate blood sugar to avoid a liver dump and the famine response. Caffiene will cause a dump, too.
"Dawn effect" / high morning blood sugar happens with some folks. It's usually best to eat to avoid it, when possible. It's common in diabetics, and folks who have their diets upside down.
Remember: breakfast like a king; dinner like a prince; supper like a pauper (unless you just trained).
100 grams carbs with a 60/40 split of fast (60 / sugars) and slow (40, starch), along with 40 to 60 grams of protein post workout is a good place to start for after workout recovery.
30 to 50 grams of lower gyclemic index carbs (starch or frutose), along with about 40 grams of protein pre workout and some caffiene will be good pre-workout.
You shouldn't generally train in ketosis, nor with your blood sugar over 200.