It was once believed, even by myself, that fat loss would occur more so an empty stomach (fasted state) when exercising. Those who knew this technique would practice it by performing a cardio fat burning style workout first thing in the morning while glycogen stores were depleted via fasting through the night (not eating).
Much new research has in fact shown that eating before a fat burning workout is superior. A study in Italy at the University of Padua tested various college age men. Men in the two groups either had a light meal before their run on the treadmill or did not eat prior to their run.
Researchers found that the fed subjects had a higher metabolism during the workout and up to 12 hours later. Fat use was also higher among the college men who were fed prior to exercise. So, for those who are thinking they are getting away with something by not eating are mistaken. It is best to eat a light meal 30-60 minutes prior to exercise if your goal is to lose body fat. (International Journal Sports Nutrition Exerise Metabolism, 21:48-54, 2011)