The question of the year and a very important one at that. There is so much information out there and there is a very big misconception that you should not eat before you train because you wont "burn fat". It has happened time and time again with new clients showing up to a weight training session in the morning with an empty stomach and very rarely will we make it through a full training session. They will either be buggered or feel dizzy from low blood sugar levels.
So before any weight training session or moderate to high intesity cardio session you need to have something to eat beforehand. You need to fuel your workout, remember food will give you the energy to train. Its best to eat an hour or so before your session so it is fully digested. There is nothing worse then training hard and your food is still sitting in your stomach. Soemtimes its not possible to eat beforehand which is where your protein shakes can come in handy especially first thing in the morning as they are digested in 20mins.
The only time it is ok to exercise on an empty stomach is when you go for a low intensity walk first thing in the morning, also known as fasted cardio. I would only go for max 45mins though on an empty stomach.
So whats the best thing to eat first thing in the morning to fuel your workout? Well always include a low GI carbohydrate such as oats or brown bread, these are a perfect pre-workout carbohydrate, include some protein such as yohgurt, eggs or a protein shake and some fruit such as berries or a bannana.
When you fuel your workout with proper nutrition you will see a big difference in your energy levels and will be able to train much harder.