In this new study, Karen Hardy from Autonomous University of Barcelona in Spain and her team brought together data to argue that carbohydrate consumption was critical for the accelerated expansion of the human brain over the last million years. Our digestive system transforms carbohydrates into glucose which is then used as energy.
The human brain uses up to 25 percent of the body's energy budget and up to 60 percent of blood glucose. 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, the study noted. Moreover, human pregnancy and lactation place additional demands on the body's glucose budget and low maternal blood glucose levels compromise the health of both the mother and her offspring, the authors argued.
They pointed out that starches would have been readily available to ancestral populations and that while raw starches are often only poorly digested in humans, when cooked they become far more easily digested. The increase in the amount of salivary amylase genes in humans also increased our ability to digest starch.
While the exact date when salivary amylase genes multiplied remains uncertain, genetic evidence suggests it was at some point in the last one million years, said the study published in the journal The Quarterly Review of Biology.