The biggest distinguishing feature which separates humans from other mammals is the size of our brain in comparison to the size of our bodies. There is, however, another factor which comes into play with our large brains.
That factor is the amount of energy that the human brain consumes. Although it represents 2.5 % of our total body weight, the brain consumes 22% of the human’s energy at rest. In other words, it takes a lot of calories to keep our brain functioning.
Taking the above into consideration, one has to ask what actually happens in our bodies when there is not enough food?
The human brain developed a unique biological pathway where an alternative source of calories is utilized during starvation. Let me explain:
Daily food intake provides the glucose the brain needs. Between meals the glycogen stored in the liver and muscles is broken down and this supply the brain with a steady stream of glucose (blood sugar). Metabolism shifts when glycogen stores are depleted and gluconeogenesis takes place which involves the construction of new glucose molecules through the harvesting of amino acids during the breakdown of muscle protein. Muscle-breakdown during starvation is however not good for humans (hunter-gatherers) as we need to move around in order to obtain food. This becomes a problem when our muscles break down due to starvation and we cannot move or lack the energy to move.
Fortunately, humans have another pathway to provide fuel for the brain – body fat – adding to the factors which distinguish humans from other animals. When body fat is used as a source of energy, ketones are produced.
Ketones slow down the disease process in the brain, allowing us to remain cognitively engaged, (keep our wits) which in turn allows us to be more likely to survive starvation during a famine.
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