Before we address this week’s myth specifically, let’s get one thing straight - for performance alone, it is almost always more beneficial to eat before exercise, regardless of the modality or intensity. If you want to perform at your best, you are almost always going to do so in a fed, rather than a fasted, state.
So, why is it that we are led to believe that performing cardio on an empty stomach is a superior option? That we will end up losing more body fat (or weight) by doing cardio fasted? Well, there is an element of truth to the idea that you will burn more fat when doing cardio fasted… it’s just not the whole picture!
When performing cardio (or any exercise for that matter) on an empty stomach, you are going to burn more fat for fuel (as you have less food/carbohydrates to use as fuel), which is logical. However, once you’ve eaten and are in a fed state, you wont continue to burn fat at a higher rate. When we consider that energy expenditure in fed and fasted cardio are almost identical, this doesn’t add up to a net increase in how much fat you’ve burned off at the end of the day. The idea that fasted cardio somehow ‘boosts’ your metabolism is simply untrue.
You will also burn more muscle when you exercise fasted (again, as there’s no carbohydrates available for your body to use as fuel), but will also build that muscle back more easily once fed (so long as you get sufficient protein in). Generally speaking, it will balance out over the longer-term of the day or even the week.
Ultimately, there’s very little difference between fasted and fed cardio - whether it be in regards to fat burning, muscle preservation, effect on caloric intake or metabolism. Thus, it comes down to one simple thing - personal preference. Some people prefer to get up and do their cardio straight away, without eating anything - and if that works for you, great! There is no reason not to perform fasted cardio if it is of your own personal preference. However, if you struggle to perform cardio fasted - if you lack energy when doing so - then there is no reason for you to do so. You should simply choose fasted or fed cardio based on what feels better for you personally.
We do, however, always recommend eating something before performing strenuous exercise (very intense cardio or resistance training), as being in a fasted state will have a far bigger impact on performance and how you feel.