When you exercise on a full stomach food is fuel, and while hitting the gym straight after eating is not a good idea, having some (at least partially) digested food in your system means your muscles are stocked with the glycogen they need to work their best.
A study showed that exercisers who ate breakfast before working enjoyed significantly higher VO2 (a measure of energy expenditure) and fat-burn rates compared to those who hadn’t eaten breakfast before exercising.
The best part? The calorie-torching edge lasted for a full 24 hours after working out!