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Archive for November, 2014

Does training on a empty stomach burn more fat?

Another typical question I get asked is ¨Does training early in the morning before I have had anything to eat  burn more fat?¨. And the answer to that is ¨ it is complicated¨. You see, when you wake up early in the morning there is a reduction in circulating blood sugar due to the fact that you haven´t had anything to eat during 6 to 8 hours. This causes glycogen (stored carbohydrates) levels to fall. This means technically that your body has to rely more on fat, rather than glucose, for energy. So you do burn more fat calories during that training session but, as I have stated before in different blogs, high intensity interval training (HIIT) is superior for fat loss than steady-state exercise (1-5).  But, have you ever tried doing HIIT with an empty stomach? I bet you didn´t get too far. You see, to perform high intensity exercises, your body needs  glycogen (quick energy). If you haven´t had anything to eat in 6-8 hours your glycogen levels are depleted, meaning you WON´T be able to train at a high intensity.  Also, if you decide to train on a empty stomach you increase the amount of tissue proteins (muscle) burned for energy during exercise (6-7), that is a big NO NO if your aim is to lose fat.

So to clarify things a bit:  if your workout consists of a slow to a brisk walk then yes, you will probably burn more fat calories if you are on a empty stomach but, you should look at the big picture. A slow to fast walk won´t burn too many calories and won´t cause you any post-exercise oxygen consumption (click here), meaning after the training you won´t be burning more calories. HIIT does produce post-exercise oxygen consumption(8) (up to 72 hours) and you need energy for that!! So my recommendations are:


Hope you like, until next time


  1. Tremblay A, Simoneay JA, Bouchard C. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism 1994 Jul;43(7):814-8.
  2. Stephen H. Boutcher. High_ Intensity Intermittent Exercise and Fat Loss. J Obes. 2011; 2011: 868305.Published online Nov 24, 2010. doi:  10.1155/2011/868305
  3. Smith, A. E., et al. Effects of β-alanine supplementation and high-intensity interval training on endurance performance and body composition in men; a double-blind trial. Journal of the International Society of Sports Nutrition 6:5, 2009.
  4. Talanian, J. L., et al. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. Journal of Applied Physiology 102(4):1439-1447, 2007.
  5. Tjonna, A. E., et al. Superior cardiovascular effect of interval training versus moderate exercise in patients with metabolic syndrome. Medicine & Science in Sports & Exercise 39(5 suppl):S112, 2007.
  6. Schoenfeld BJ, Aragon AA. Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the international society of sports nutrition 2013,10:5
  8. Treuth, M. S., et al. Effects of exercise intensity on 24-h energy expenditure and substrate oxidation. Medicine & Science in Sports & Exercise 28(9):1138-1143, 1996.



onathan P Little, Adeel S Safdar, Geoffrey P Wilkin, Mark a Tarnopolsky, and Martin J Gibala. A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle: potential mechanisms. The Journal of Physiology, 2010; DOI: 10.1113/jphysiol.2009.181743


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