People say it means you burn more fat.  What does the research say?

Fasted cardio increases fat burning compared to fed cardio while exercising [1].

However there will be no difference in the long run [2]  


If you burn more fat during exercise, your body makes up for it later by burning less fat during the rest of the day [3].

Body composition changes associated with aerobic exercise in conjunction with a hypo-caloric diet are similar regardless of whether or not an individual is fasted prior to training.

Hence, those seeking to lose body fat conceivably can choose to train either before or after eating based on preference.

Fasted training is suitable for most people but may reduce performance depending on training duration and intensity [5].

Overall most of these effects are small.

If you enjoy cardio before breakfast, go for it.