After a meal, much of your energy and blood flow is focused on digestion, so I wouldn't recommend exercising right after a meal. A light snack of fruit or cheese would probably be ok though. If you want to maximize fat loss during the workout, then don't eat anything several hours before hand that is high in sugar or refined carbohydrates since these will raise your bloodsugar and insulin levels. If your bloodsugar is high, then your body doesn't need fat for fuel. If your insulin level is high, then fat metabolism is effectively blocked.
The tragedy of science is the slaying of a beautiful hypothesis by an ugly fact. T H Huxley