You may have heard a lot about “fasted cardio” (if you’re not already doing it). Whether through social media, locker room talk, or a fitness blog, it’s grown in popularity, especially in the competition industry, over the last few years. It’s easy to think that if so many people are doing it there must be something to it, right? But is this really the case?
If you enjoy doing your cardio first thing in the morning and feel that it works well for you, then by all means keep doing it. But research has shown that early morning cardio in a fasted state is not only unnecessary but could actually be less effective for calorie burning and total fat loss. The growing trend of so many people doing fasted cardio is due more to popularity combined with a misunderstanding or misinterpretation of available science than actual results.
The truth is that it is not necessary, or as mistakenly believed, a scientific advantage to do “fasted cardio” in order to lose body fat. There’s research that has supported this for quite some time. While it may seem more hardcore and dedicated to get up first thing in the morning and, without eating any food, soldier off to the gym to put in work, it’s not really necessary for fat burning in terms of how the body actually responds.
Yes, doing cardio when glycogen (stored carbohydrates) is lower and cortisol levels are higher (a condition that exist when you’re in a fasted state as in the morning when you wake up- and also after intense weight training btw) will cause the body to break down more fat into fatty acids (lipolysis). This fact is what has led many to conclude that doing morning cardio in a fasted state is the best approach for cardio results. The problem is that the body is not able to burn/utilize (oxidation) the extra “broken down” fat and that is the key (and the other scientific fact) so it just re-absorbs it. So you don’t actually burn more fat as was the goal. In addition, newer research has concluded that cardio done in this fasted state is catabolic in nature (muscle wasting), something that was always strongly suspected. If you’re breaking down muscle from increased catabolism it will have a negative effect on your metabolic rate which of course will effect your ability to lose and keep off body fat, not to mention the potential effect the lost muscle can have on appearance and performance. Research has also shown that you do not burn more total calories during the day from doing fasted cardio and often burn less. Without glycogen, the body is not able to generate or sustain the same level of intensity during exercise which also lessens the amount of calories your body will burn both during training and post-workout while you rest/recover.
So what does this mean for you? If you’re already doing fasted cardio and feel it’s working for you, go right ahead and keep doing it! If you start to lose muscle or feel your energy is suffering try eating first (at least some protein food or a shake, bcaa’s, or a light meal). If you’re not currently doing morning fasted cardio, just know that you don’t need to wake up at some undesirable hour, make a special trip to the gym and forgo a morning meal to make your cardio workout be an effective part of your weight/fat loss program (especially if you plan to do HIIT- you will need the fuel). If you’re doing your cardio post weight training and feel that is working well for you, keep at it as you are getting the same perceived benefits as being fasted (lower glycogen and blood sugar, higher cortisol levels and a greater degree of fatty acid breakdown). Applying science to fitness is great but not everything has been scientifically proven or disproven so there will always be the need to listen to your body, put certain things to a personal evaluation, and discover what works best for you.