Consumption of Carbohydrate especially in the form of starch was critical for the growth of large human brains over the last million years, says a new study.
Dr. Karen Hardy and her colleagues at Catalan Institute for Research and Advanced Studies highlighted their observations to build a case for dietary carbohydrate being essential for the evolution of modern big-brained humans.
The human brain uses up to 25% of the body's energy and up to 60% of blood glucose. The researchers said that while synthesis of glucose from other sources is possible, it is not the most efficient way, and these high glucose demands are unlikely to have been met on a low carbohydrate diet.
During pregnancy and lactation the demands for carbohydrates increase where low maternal blood glucose levels compromise the health of both the mother and her offspring.
Starches would have been readily available to ancestral human populations in the form of tubers, as well as in seeds and some fruits and nuts. Generally raw starches are often poorly digested in humans, but when cooked they lose their crystalline structure and become easily digestible.
Presence of several copies of salivary amylase genes in humans increases the amount of salivary amylase produced. Therefore the ability to digest starch is higher in humans than primates which has only two copies of the gene.
Co-evolution of cooking and higher copies of the gene increased the availability of pre-formed dietary glucose to the brain and foetus. This in turn may have permitted the brain to increase in size from around 800,000 years ago.