Mammoth Hunters recommends as a way to improve performance to do exercise on an empty stomach, with at least 3.5 hours between the last meal and the training session. This is called intermittent fasting.
This statement is based on scientific reasoning that human physical capacities have evolved as essential tools in order to gather food and thus we are extremely adapted to perform at our best when we are fasting.
Imagine ancient humans fighting for survival. When do you think they would feel more compelled to move, just after feasting on a big chunk of meat or a delicious platter of nuts and berries or when hunger stroke them and food was scarce?
You probably guessed it right, while fasting.
Neuronal response triggered by intermittent fasting
Once the brain feels that there is a thread, such as the feeling of scarcity, it signals to the body that is time to get active1. On the other hand when we have satisfied our hunger the body “shuts down” to keep the precious energy for as long as possible.
This adaptation goes beyond just when we feel like exercising. Intermittent fasting has some very specific advantages in terms of performance:
- The body uses as a principal energy substrate fat as a means to preserve our precious glycogen reserves and minimize glucose utilization. This is a very interesting metabolic shift as fat provides with more “energy units” than glycogen, although it is harder to “activate”1. Yo can read more about how fat is metabolized here.
- With intermittent fasting we develop a muscular fiber that has high “metabolic elasticity”, meaning that it 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 workouts3.
- We train our metabolic capacity to capture circulating blood glucose without the need of the insulin hormone4.
- Control of the body is centralized in our limbic system (or emotional system) that requires physical activity in order to get food. The hormone dopamine is released which reduces the feeling of exhaustion5.
Intermittent fasting and sport
These list above enumerates just a few of the advantages of intermittent fasting, but not the only ones. Physiological stress due to exercise and fasting are regulated by different molecular mechanisms that have synergistic effects. The main regulator of energetic homeostasis in our body is the protein AMPK that acts as a messenger signaling for increase in the efficiency of glucose capturing, fat oxidation and increase of mitochondria synthesis (through activation of the expression of PGC-1 gene). Mitochondria are the power plants of our cells either degrading glucose in presence of oxygen or recycling lactate in anaerobic conditions, and their density in the cell is a key factor on long and intense races.
Training while fasting creates a signal of energy depletion in our system, which activates AMPK expression, followed by PGC-1 expression and ultimately an increase of mitochondrial synthesis which leads to more efficient energy utilization and higher performance.
After all why would you hunt a mammoth if you have just eaten one?
- 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.
- Storlien L, Oakes ND, Kelley DE, Metabolic flexibility. Proc Nutr Soc. 2004 May;63(2):363-8.
- 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.
- 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.