Fasted cardio is one of the hottest topics amongst dieters, especially those who compete in body building. The idea of doing cardio on an empty stomach first thing in the morning makes sense to some people – with no immediate source of energy, won’t your body burn stored fat for energy? There’s compelling evidence for and against fasted cardio, so I thought I’d break down the main points of various studies for both sides and let you chose.
FOR FASTED CARDIO
One study that is often cited (Bonen, A. et al. (2008). Effect of training in the fasted state on metabolic responses during exercise with carbohydrate intake. Journal of Applied Physiology. Apr;104(40):1045-55) showed that training fasted actually increased your muscle glycogen stores, making it a great adjunct to endurance athlete’s training. The idea is that increasing the body’s ability to store glycogen will allow athletes to compete at higher intensity long term.
Another study looked at supplementing your fasted cardio with caffeine and yohimbe and found that this increased catecholamines in the body, which helped to break down fat stores more readily. So fasted cardio, at least in the short term, increases the bodys’ ability to burn fat.
But, that’s pretty much where the science ends. The idea of fasted cardio – that your body would used its reserves instead of readily available food – was greater than the research. Now powerhouses such as Dr. Layne Norton and pretty much all of science have decided the cons far outweigh the pros.
AGAINST FASTED CARDIO
A lot of data for this comes from a study done through The Strength and Conditioning Journal (Volume 33). They found that the thermogenic effect of exercise (that is, your long term calorie burn) is HIGHER if you’ve eaten before exercise. They also found that training fasted decreased your overall energy output, so if you felt sluggish you didn’t put as much effort into a training session as someone who ate before.
What is more alarming than this is the catabolic effect fasted cardio can gave. Muscle catabolism is exactly what everyone wants to avoid – why train fasted if you could possibly lose muscle in the process? Proteolysis (the break down of protein) is higher in fast training and nitrogen losses more than doubled in this state.
So what’s the take home message with these studies? Know your goals. If you’re trying to maintain muscle and lose fat then eating something before doing your cardio (oatmeal, BCAAs, egg whites, pop tarts, etc.) can help you from losing muscle and keep your energy high. If you’re an endurance athlete then fasted cardio can contribute to your glycogen stores. With this information you can make appropriate decisions based on your own goals and levels of fitness.