Doing cardio on an empty stomach, usually first thing in the morning, is supposed to help you burn more body fat than eating before your run, ride or swim. But is this scientific fact or just another popular gym myth?
A study published in the Journal of the International Society of Sports Nutrition compared the effects on 20 young female subjects who adhered to a hypocaloric diet for a month. Half of these subjects put in an hour of steady state cardio exercise 3 days a week without eating since the previous evening. The other half eat breakfast before training. All adhered to a diet designed to burn more calories than consumed. At the end of the program, both groups lost weight and reduced fat mass.
Conclusion: There were no significant differences between groups. As long as you’re cutting calories, having a small, balanced meal before training might outweigh the benefits of not eating first.