Tag Archives: cardio on an empty stomach

  • Is cardio on an empty stomach good for weight loss?

    Great question.

    Research has strongly concluded to date that the most effective form of cardiovascular exercise for weight loss is high intensity interval training (HIT). Considering that there are no medical concerns and that you have been cleared by a professional (both medical and fitness) to perform this style of cardio safely, then this is the form of cardio that you should be considering.

    Cardio exercise on an empty stomach with high intensity training does have significant drawbacks as I'll explain below:


    With high intensity cardio that you will be performing, the primary energy source that you will be utilising during your workout will be carbohydrate. Carbohydrate is available both from the foods that you consume and also glycogen (carbs stored within the muscles).

    If you exercise having not eaten for over eight hours, your ability to source carbohydrates will be greatly diminished. Your glycogen levels will be quickly depleted and you will have no ready access to carbs from your diet. Thus, your intensity will greatly diminish. A lower intensity means that fewer calories will be expended, potentially resulting in a decreased ability to oxidise fat AFTER your workout has completed. Also, a lower intensity means that your body's fitness response will be reduced.

    This also brings us to the second point:

    Muscle Catabolism (or muscle breakdown)

    Since carbohydrate is not readily available, your body has two other desirable (in it's eyes) options: fat tissue and muscle tissue.

    Fat tissue is slowly oxidised (or broken down) - hence why it is a primary energy source for low intensity cardio. When it comes to high intensity cardio, fat cannot provide the required energy quickly enough to sustain this level of output. Consequently, muscle tissue is utilised at a higher priority. This means that a significantly higher degree of muscle tissue is broken down to generate energy to fuel your body through the workout.

    In order to reduce the degree of muscle that is lost during (and after) your workout, the optimal approach is to consume a carbohydrate rich food prior to your workout, in addition to a protein source also.

    Optimal Fat Oxidation (or fat breakdown)

    The majority of fat loss occurs after your workout, when you go through a period of "excess post-exercise oxygen consumption" (or EPOC). The notion that it is more effective to perform cardio on an empty stomach is based on the premise that most of the fat loss occurs during your workout and thus by exhausting other energy options, you can "target" fat oxidation more effectively. However, at a high intensity, minimal fat loss occurs "during" the workout. The vast majority of fat loss occurs after the workout, during the EPOC period.

    Here are a few articles for further reading that I strongly recommend you review if you haven't already:

    Myths Under the Microscope - Fat Burning Zone
    The Fat Burning Zone
    Fasted Cardio

  • Should I perform cardio on an empty stomach first thing in the morning? I have lost 30kg so far with the help of a dietitian, but am unsure if fasted cardio is the best way to lose weight.

    First and foremost, a big congratulations on losing 30kg of weight!!  That's amazing mate.  I'm sure that means a lot to you, because I know it takes a LOT to make that initial decision to turn your life around, as you have.

    Secondly, there's no such thing as a dumb question as far as I'm concerned.  If you don't know the answer, what better way to find out than ask?

    In actual fact, it's quite a good question and something that I believe has been quite misinterpreted within the fitness industry.  I have certainly heard many people suggest that exercising on an empty stomach is the most effective way to "tap into" the fat stores.  The theory behind this is that, because you have starved yourself for in excess of eight hours (whilst sleeping), your body has little carbohydrate to draw upon.  Therefore, the primary source of energy is going to be fat tissue right?  Unfortunately, the body doesn't work that simplistically.

    What this theory fails to consider is muscle mass.  Muscle mass is actually broken down far more readily than fat tissue.  So, if you are exercising on an empty stomach, you will experience a fair amount of muscle catabolism.  Considering that muscle tissue is a classified as metabolically active (in other words, burns plenty of calories throughout the day), losing muscle tissue is extremely counter-productive with respect to fat loss.

    That's not to say that exercising on an empty stomach will not result in fat loss.  I have no doubt that you will lose fat tissue by exercising first thing in the morning.  However, considering that you will sacrifice a fair amount of muscle tissue in the process, there are more effective ways to achieve a substantial amount of fat loss.

    Another point to consider is that, what you exercise on an empty stomach, the intensity of the cardio session will be greatly impacted.  Think about it - you're running off an empty tank.  How hard will your body allow you to push?  Not nearly as hard as if you were fully fueled.  Therefore, the number of calories during the HIIT session will be greatly reduced.  Additionally (and more importantly), the overload on your body will thus be reduced and therefore less fat tissue will be metabolised after your workout has completed.

    A good approach is to perform HIIT's about an hour after breakfast so you have plenty of carbohydrates to assist in energy production.  If you want to perform low-intensity exercise to burn additional calories, but without the overload on your body, I would suggest to do so after a later meal to prevent muscle breakdown, maybe in the afternoon.  Ensure that you continue with an effective resistance training regime, as this will assist in muscle synthesis and also greatly enhance fat loss.

    A great article on this topic we have available is entitled "Myths Under the Microscope - Fasted Cardio".

    If you need any assistance with your goals, please don't hesitate to contact me.  It seems like you have your nutrition down pat with a professional, but do remember that your training is just as important for maximum results.

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