The studies are in and they say…
They say a number of things…
There is evidence to say that fasted cardio can be beneficial for burning fat (during the course of a training session) as its priority fuel source, especially when cardio is low intensity (Iwayama et al., 2015).
There is evidence that women have higher levels of fat oxidation in a fed state compared to men. Males showed an increase in fat oxidation in the fasted state compared to females (Stanard et al., 2010).
There is evidence to say that training fasted will increase proteolysis (the break down of protein structures) which may detriment the goal of increased lean muscle tissue (Schoenfeld, 2011).
There is evidence to suggest that people who eat before performing HIIT style training are likely to put on more lean muscle tissue than those who perform HIIT fasted (Gillen et al., 2013).
A study by Proeyen et al., 2010 found healthy individuals who were fed in a calorie surplus were more likely to gain body fat when training fed as opposed to fasted, although this may have been caused by discrepancies in intake from giving the fasted group a smaller feeding window or through appetite repression from training.
So what should you do?
Training fasted or fed is one of those things that gets many people caught up in minute details and stops them from taking action.
The evidence is apparently inconclusive; however, we know that fat oxidation is required over a 24-hour period for results on changing body composition, not just a 30 minute jog in the morning!
We also know that your work, lifestyle, family, social occasions etc, require you to facilitate your exercise around them! Whether you do cardio in the morning or the evening is not something to worry about as long as you are looking to lose fat, stay in a calorie deficit and do the work!
The only time I want you to really consider the effect of eating fed or fasted here is if you are looking to gain lean muscle tissue. It is clear that fasted training will ramp up AMPK (remember this? If not click here) and limit the MTOR response required for muscle anabolism and hypertrophy. This can be offset by intra workout nutrition, so don’t worry too much if you do have to train first thing!
If you are training for performance, you will do better if you eat! So make sure you are setting your goal up in line with your nutrition and training schedule!
The key takeaway here is you can train when you like, being mindful of your goal is important and individualising your approach will lead to a successful outcome!
Iwayama, K., Kawabuchi, R., Park, I., Kurihara, R., Kobayashi, M., Hibi, M., Oishi, S., Yasunaga, K., Ogata, H., Nabekura, Y. and Tokuyama, K. (2015). Transient energy deficit induced by exercise increases 24-h fat oxidation in young trained men. Journal of Applied Physiology, 118(1), pp.80-85.
Stannard, S., Buckley, A., Edge, J. and Thompson, M. (2010). Adaptations to skeletal muscle with endurance exercise training in the acutely fed versus overnight-fasted state. Journal of Science and Medicine in Sport, 13(4), pp.465-469.
Schoenfeld, B. (2011). Does Cardio After an Overnight Fast Maximize Fat Loss?. Strength and Conditioning Journal, 33(1), pp.23-25.
Gillen, J., Percival, M., Ludzki, A., Tarnopolsky, M. and Gibala, M. (2013). Interval training in the fed or fasted state improves body composition and muscle oxidative capacity in overweight women. Obesity, 21(11), pp.2249-2255.
Van Proeyen, K., Szlufcik, K., Nielens, H., Pelgrim, K., Deldicque, L., Hesselink, M., Van Veldhoven, P. and Hespel, P. (2010). Training in the fasted state improves glucose tolerance during fat-rich diet. The Journal of Physiology, 588(21), pp.4289-4302.