WASHINGTON, Aug. 6 (UPI) -- The paleolithic diet likely included high levels of carbohydrates that kick-started the evolution of modern big-brained human beings, researchers said in a new study.
Increases in in how much meat people ate and the development of cooking also have been credited with spurring the growth of the brain, but the researchers argue that carbohydrates were the key because of the amount of energy the body requires.
The researchers said links between genetic evidence that the body began to increase the ability to digest starches around 1 million years ago and the acceleration in growth of brain size starting about 800,000 years ago make it likely that carbohydrates were the catalyst for that growth.
"The global increase in the incidence of obesity and diet-related metabolic diseases has intensified interest in ancestral or 'Paleolithic' diets," researchers wrote in the study, published in the Quarterly Review of Biology. "Surprisingly, however, there is little clear agreement on what quantitatively constitutes a healthy diet, or indeed a Paleolithic diet, with much conflicting information disseminated to the public. Yet it is clear that -- to a first order of approximation -- our physiology should be optimized to the diet that we have experienced during our evolutionary past."
In the study, the researchers looked at archaeological, anthropological, genetic, physiological and anatomical data to come up with a set of central observations building their case for carbohydrates being essential to the paleolithic diet.
The amount of energy required by the brain alone -- 25 percent of the body's energy and 60 percent of blood glucose -- likely could not have been supplied without carbohydrates. The same is true for glucose requirements during human pregnancy and lactation, and low blood glucose would have been dangerous for the mother and the baby, they write.
It's likely that starches would have been easily available in the form of tubers, seeds, nuts and fruit. Human development of cooking also was significant, as cooking starches makes it easier for the body to digest them. Increases in production of salivary amylase, which helps to digest starches, are also thought to have started at some point in the last 1 million years -- not long before the brain began to grow.
"Although previous studies have highlighted a stone tool-mediated shift from primarily plant-based to primarily meat-based diets as critical in the development of the brain and other human traits, we argue that digestible carbohydrates were also necessary to accommodate the increased metabolic demands of a growing brain," researchers write.