It may seem somewhat logical that your body would burn more fat as fuel when you exercise on an empty stomach first thing in the morning. In fact, it just isn't true. The body needs fuel to work out, and that fuel is glucose, which comes from carbs.
After a full night's rest, your muscles' supply of glycogen, which is stored glucose, is greatly depleted. Not only do your muscles run on glucose, but so does your brain. Working out on an empty stomach can impair both muscle function and some brain function as well, and exercising with a fuzzy head in the early morning can lead to injuries.
The simplest way to fuel your body and feed your muscles before hitting the road, elliptical, or weights is a light carb snack. Try an easily digestible banana, or just half of the fruit and save the other half for your post-workout smoothie. Another good pre-workout snack would be some yogurt or a small amount of cereal with milk. I have found a simple rice cake works wonders before a 6 a.m. spin class.