Does morning cardio burn more fat?

 Many people seem  to believe that aerobic exercise during a fasted state (many call it "morning cardio") burns more fat than arobic exercise on a non fasted state. Could it be the the hidden secret to fat loss?!

From a scientific point of view it's both true and false. But before reading further I would like to remind you that; there are NO shortcuts or magic do's to fat loss. The work has to be done and the unnecessary calories left uneaten, independent of the time of the day, if you want results.

Fact 1#  Yes, doing low impact aerobic exercise on a fasted state burns more fat than doing the exact same exercise after eating WHILE exercising (<65% Max heart rate). This intensity is for most a brisk walk.

Fact 2#  Exercise in a fasted state increases the risk of a katabolic effect by over 50%, meaning that you end up burning muscles, that's not the road to successful training.

Fact 3# Exercising with a heartrate over 65% of max, during fed state, burns most likely more fat in the long run due to the EPOC (excess post oxygen consumption) also called the "after burn" and the increased energy expenditure that the increased intensity gives. This "increases intensity" over 65% of MaxHf is an intensity that, of course, depends on the persons aerobic level, but for most hobbyist trainers it's everything above brisk walking and super light jogging.

Fact 4# Studies also show that EPOC increases if you eat before a workout. Exercises with a fueled body also gives your body the full potential to recover itself; becoming stronger and better. 

Conclusion:

- It is beneficial for burnng fat if you are doing recovery, low impact workouts under 65% of maxHF. Unless you are in athlete shape this low impact intensity is nothing more than a brisk walk,

- If you feel like doing a proper run, to increase your aerobic level, I would suggest eating something small before or wait with it until later on the day. 

The pros and cons are in the end minimal and as I mentioned before there is no magic rule or quick fix. Just do it, as Nike would have said, or whatever floats your boat.
In the end it's up to you whether you are an early bird or not. And how well your body responds to exercising in a fasted state. However the feeling of burning the cande in both ends should be avoided.

Why not exercise for better performance?
   - The benefits of fat loss is just a small plus on the side.

Lets look at aerobic exercise in the morning from another viewpoint; increased performance. It's good to periodize your day if you are a professional athlete or someone that for some reason exercises A LOT, (two times a day or more). This helps the body to recover as much as possible between the exercises, meaning its beneficial to do one workout in the morning and another one later in the afternoon. Exercising like this usually means that one is easy and the other one hard.

Many athletes actualy eat TWO breakfasts in the morning.  Usually it takes a while for the body to wake up and food perhaps doesn't taste as good early in the morning. Also there is the risk of tasting your breakfats two times if you train directly after eating a big steady breakfast. Preferably athletes tend to eat something light and easily absorbed before a morning workout, like a smoothie, shake or porridge. After the morning workout it's time for a proper breakfast that gives the body fuel for recovery and upcoming tasks during the day.  

Doing vigorous exercises on a fasted state does not give the body energy to perform at best nor energy to recover properly; Meaning that you don't exactly help your body to become better or stronger.

References:

Bennard P. & Doucet E. 2006.  Acute effects of exercise timing and breakfast meal glycemic index on exercise-induced fat oxidation,  Pub Med.

Lemon PW,  Mullin JP. 1980. Effect of initial muscle glycogen levels on protein catabolism during exercise. Pub Med.

Saris WH, Schrauwen P. 2004. Substrate oxidation differences between high- and low-intensity exercise are compensated over 24 hours in obese men 2004, Pub med.

Bahr R, Sejersted OM.  1991. Effect of intensity of exercise on excess postexercise O2 Consumption, Pub Med.

Melanson EL, Sharp TA, et al. 2002. Effect of exercise intensity on 24-h energy expenditure and nutrient oxidation. Pub Med.