I have been asked this question at least 5 times in the past week alone; “Should you eat before you train in the morning?” For many, the belief is that if you do not eat, you will have no readily available fuel in the form of carbohydrate, and as a result you will burn a greater proportion of fat. Unfortunately things are not so clear-cut when it comes to physiology and fat metabolism.
If no carbohydrate is available to the muscle when it is being trained, while you will burn a higher percentage of fat overall, but of a likely smaller amount of total energy, as the body will reduce metabolism to adapt to the perceived fuel shortage. For this reason, if you complete a light training session of <30 minutes of moderate intensity activity, before 730-8am, you do not need to eat before you train. But, if you train for >45-60 minutes, have cut out carbs the night before and/or will not eat your breakfast until after 8am you are likely to train more efficiently and burn more fat if you do eat a small portion of carbohydrate before your session. Please note, small, just 10-20g, which will top up your blood glucose level and let you access your fat stores more efficiently. Good choices include 1 slice of toast with peanut butter or cheese, a couple of Vita Weat crackers and ½ glass of milk.