Why you should be working out on an empty stomach

Imagine ancient hunter gatherer societies fighting for survival with hardly any food reserves. When do you think they used to move: Just after feasting on a big chunk of meat or when they were hungry and didn’t have food? Obviously when they had to go and find food. They’d rather take a siesta after the meal.


We have always recommended doing your workouts on an empty stomach with a gap of at least 3.5 hours after the last meal. It is based on evidence that the physical capacity of human beings was selected as a basic tool to procure food and therefore, the optimal body condition for physical activity is fasting. This post explains the benefits of working out on an empty stomach and why this helps you improve your performance and lose weight better.

Benefits of working out on an empty stomach

When the brain feels that there is a threat, such as the feeling of scarcity, it signals to the body that it’s time to get active1. On the other hand, when we have satisfied our hunger, the body “shuts down” to conserve precious energy for as long as possible. In addition to being more natural, working out on an empty stomach has some very specific advantages in terms of improving your performance:

1) Burn more fat
It promotes the use of fat as the main energy substrate, in order to preserve glycogen reserves and minimize the usage of glucose. This is a very interesting metabolic shift as fat provides more “energy units” than glycogen, although it is harder to “activate”1. You can read more about how fat is metabolized here.

2) Develop better muscle fiber
Working out on an empty stomach helps us develop a muscle fiber that has high “metabolic elasticity”. This fiber can perform very well at both long physical efforts required in endurance training while maintaining the capacity of high explosive potential for short and intense workouts2.

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3) Capture glucose without Insulin
Training while fasting stimulates muscle glucose receptors called GLUT4 that mobilizes the cell membrane in a way that prioritizes the muscles to receive glucose3. All this happens without the body having to release insulin. So in addition to improving our performance, it greatly benefits people suffering from glucose regulation or obesity issues.

Glucose Insulin Exercise GLUT4

4) Less fatigue
When the movement of the body is coherent with what the emotional system wants (go get food), we release a neurotransmitter called dopamine that makes us more tolerant to fatigue4. Dopamine is also associated with cognitive ability, motivation, pleasure and is considered to be the the biochemical translation of the phrase, “a sound mind in a sound body”.

5) Boosts endurance and performance
The energy stress caused by exercise during fasting affects the proteins that regulate energetic homeostasis. This transmits a signal to cells to improve glucose uptake, increase fat oxidation and synthesize new mitochondria. Mitochondria are the power plants of our cells and its density plays a key role in long and intense races.

Although the list above enumerates a few vital metabolic functions that are boosted by doing your workouts on an empty stomach, the most obvious reason is: Why would you hunt a Mammoth if you’ve just eaten one?

  1. Peters, A., Schweiger, U., Pellerin, L., Hubold, C., Oltmanns, K.M., Conrad, M., Schultes, B., Born, J. & Fehm, H.L. 2004, “The selfish brain: competition for energy resources”, Neuroscience and biobehavioral reviews, vol. 28, no. 2, pp. 143-180.
  2. Storlien LOakes NDKelley DE, Metabolic flexibility. Proc Nutr Soc. 2004 May;63(2):363-8.
  3. Zorzano, A., Palacin, M. & Guma, A. 2005, “Mechanisms regulating GLUT4 glucose transporter expression and glucose transport in skeletal muscle”, Acta Physiologica Scandinavica, vol. 183, no. 1, pp. 43-58.
  4. Foley, T.E. & Fleshner, M. 2008, “Neuroplasticity of dopamine circuits after exercise: implications for central fatigue”, Neuromolecular medicine, vol. 10, no. 2, pp. 67-80.

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