The notion that exercising in a fasted state in the morning yielded greater fat loss was based on the fact that storage of glycogen (the stored form of glucose) is much lower after a night of sleep. Your body prefers to utilize stored glycogen first, then stored fat when it comes to fueling workouts. So the theory makes sense but had never really been tested until a few years ago. An Italian study wanted to understand whether it was more beneficial for fat loss to exercise in a fed or fasted state in the morning.
The study involved eight men who over the course of two weeks, exercised in both a fed and fasted state, with a week in between each. They had all the men complete the same workouts (36 minute treadmill exercise) and eat the same daily calories and macronutrients, and only changed the timing of their breakfasts. Researchers then collected calorie expenditure data for 12 and 24 hours post workout.
The study found that participants burned slightly more calories 12 and 24 hours post exercise in a fed state than in a fasted state. Even more interesting, the fat calories that were expended after exercise was more for the fed state compared to the fasted state. So the argument that exercising in a fasted state is more effective for fat loss is not supported by this study’s results.
It would make sense that exercising with some immediate fuel would allow for a more intense exercise session. I have always recommended that my clients eat a light breakfast before their morning workout so their muscles have something to tap into to survive a workout. A light easily digestible breakfast such as fruit and nuts; a smoothie; piece of toast and peanut butter; energy bar would be the best. For greater fat utilization during and after the workout choose low glycemic carbohydrates. Avoid anything heavy like eggs, dairy, bacon, etc. if you do not have at least an hour before your workout.
The controversy over which state is more effective, fasting or fed has been busted. Now go forth and prosper.