Let me start off by saying that I was once a preacher of fasted cardio. I did it steadily for about 8 months, 2-3 days per week in hopes that it would help shed excess body fat. For those who are unaware, fasted cardio simply means to perform LISS (Low-Intensity Steady State) cardio without consuming any food, protein, or even BCAAs beforehand after an overnight fast. I can state from experience that I was not any leaner from performing this type of cardio, in fact I am leaner NOW that I perform only a few HIIT (High-Intensity Interval Training) sessions per week. Let’s get down to the science…
The theory behind fasted cardio is that you will burn more fat as a result of your glycogen levels being depleted after an overnight fast. It is important to realize that fat burning is not immediate. You don’t just burn fat after an hour sweating on the treadmill. In fact, fat burning takes place over a series of days and research from the S&C Journal shows that the more carbohydrates you burn during exercise, results in more fat burned after exercise has ended. Brad Schoenfeld is the author of the journal article and in summary, he states that fasting before exercise actually reduces the thermogenic response to exercise compared to not fasting. What does this mean exactly? If you eat before a workout, you will increase thermogenesis (increase in body temperature which burns calories).
Not only that, but the article also discusses another negative factor to fasted training which is the breakdown of proteins (AKA proteolysis). If you are trying to build muscle, fasted cardio is more than doubling the loss of nitrogen (compared to normal cardio) which is key when it comes to building and retaining muscle.
Now that you have the scientific evidence supporting normal cardio over fasted cardio, I’m sure there will be people who are thinking, “What if I don’t LIKE to eat before a workout?”. Do you find that eating a full meal before working out makes you feel sick or too full? My solution for you would be to consume a liquid meal as opposed to a full on breakfast or dinner- depending on the time of day you exercise. About an hour before you are ready to hit the gym, I would suggest to consume a shake that is full of protein as well as those beloved carbs to ensure you are fueled properly. This is especially important if you are trying to maintain or build muscle. An example liquid meal for me would be 1 scoop of Whey Protein blended with ice, water and a banana. The banana is a simple carb which will be digested and ready to fuel your body within the hour.
There truly is no reason to suffer as a fasted cardio-goer every morning. I am a firm believer that you should not only be backing your theories with scientific evidence, but you should also be doing activities that you love and that will benefit your body to it’s maximum potential.
Schoenfeld B. Does cardio after an overnight fast maximize fat loss? Strength and Conditioning Journal, 2011(33): 23-25.