There are a lot of early birds who like to wake up before the sun comes up and exercise first thing in the morning, before eating breakfast. While this can be tempting to save time, it might not be the best idea.
Most Important Meal of the Day
The reason breakfast has been labeled the most important meal of the day is because before it, the last time you touched any food was 8 or more hours ago. For 8 hours, you've effectively starved yourself. When you don't eat for long periods of time, your body starts to break things down for energy. It'll go to the liver and breakdown glycogen for sugar and it can also start breaking down muscle tissue to convert into sugar for more even more energy if it needs to.
If you wake up and eat something, even a small snack, your body will digest the food and won't need to look anywhere else for the energy it needs. If you workout before eating, your body will be in need of more energy and will break down muscle to get it.
It is very important that you eat something before exercising in the morning no matter how small it may be. Even a 100-200 calorie snack will go a long way in preventing muscle breakdown (granola bar, yogurt, cup of chocolate milk).