Fasted Cardio

There have been some questions regarding fasted cardio lately so I will try to explain without being too boring to answer some of them.

Understanding the science behind fasted cardio, along with an indvidual’s unique set of goals, will provide the most clear-cut plan.

When you’re sleeping, the primary substrate used as fuel to power your breathing, digestion and circulation is your fatty free acids. When you wake up, many fatty free acids are decloalized or let go from usual activity and therefore can be used as fuel. This is why I suggest doing light to medium cardio on an empty stomach. 

Another thing that must be considered is the state of the body before sleep. In order to only use fat as the fuel during your fasted cardio session, your glycogen (sugar) stores must be depleted. So, if you don’t go to bed with these stores depleted, then these sugar stores will be used before any of the fat during your cardio session.

When you fast over night and perform your cardio in the morning, you significantly lower the insulin in your blood. Once these levels are lowered, your body will increase lipolysis (fat splitting). This occurs because insulin triggers a messenger response inside the fat cells to break them down and be released for fuel.

So the main question to answer is at what intensity should you perform your cardio session in a fasted state? I suggest somewhere between 60-65% of your heart rate max. To figure this out quickly just take 220-your age and multiply by .60 or .65 to get your number. Try to keep you heart rate at this number for at least 30 minutes and upwards of 60 minutes. 

Why shouldn’t you perform cardio at a higher intensity? The main reason is the hormone cortisol. Cortisol is the hormone released during intense or stressful situations and can be very damaging to the body. It can also break down hard earned muscle. Intense exercise puts an enormous amount of stress on the body which increases the cortisol’s effects. During early morning hours when you awake, cortisol levels are at their highest. This means that if intense exercise is performed, not only is muscle potentially at risk, the body is less likely to use fat as it primary source of fuel.

To wrap this up, I suggest the mornings that you are properly fasted from the night before and would like to burn some honest to goodness fat, peform fasted cardio at an intensity that is no more than 65% of your heart rate max. This will probably be a “power-walk” for most. Don’t let that pesky cortisol have its way with your body by trying to go more intense! Trust me on this one! Good luck to you!!