Energy-hungry childhood brain slows growth

A child’s brain is voracious, burning up twice as much energy as an adult’s brain, something that could help explain why children around the age of four or five grow so very slowly compared to other animals, new research suggests.

Horses are up and running soon after birth and thoroughbreds are racing by age two. Chimps are adults at between 12 and 15 years. But human toddlers seem to grow particularly slowly and researchers believe this is because the brain claims most of the calories consumed.

“Our findings suggest that our bodies can’t afford to grow faster during the toddler and childhood years because a huge quantity of resources is required to fuel the developing human brain,” says Prof Christopher Kuzawa a professor of anthropology at Northwestern University’s Weinberg College of Arts and Sciences.

He is first author of a study published this evening in the Proceedings of the National Academy of Sciences. Humans at that age have a lot to learn "and that learning requires a complex and energy-hungry brain", he says.

A four-year-old's brain accounts for 40 per cent of the child's total energy expenditure and gobbles up glucose, the fuel that powers us all, at a rate comparable to 66 per cent of the body's resting metabolic rate, the researchers say.

This heavy consumption reaches a maximum at about five years. It is related to the high energy demand required by the brain as it builds synapses and connections that will serve as the child grows into adulthood, according to the multi-centre project funded by the US National Science Foundation.

"Body growth grinds nearly to a halt at the ages when brain development is happening at a lightning pace because the brain is sapping up the available resources," says Prof Kuzawa.

Human children burn up more energy than other primate species, but grow during this time at a pace more akin to that of a reptile rather than a mammal, the authors say.