The Brain Gobbles up Almost Half of a Child's Energy—When This Changes the Risk of Obesity May Increase

A child's brain uses almost half of the body's energy in the early years of life, and scientists are now hypothesizing that the period in which a kid's brain stops consuming so much fuel comes with the risk of becoming obese.

Scientists at Northwestern University and the New York University School of Medicine looked at existing studies to investigate the link between the adiposity rebound and the glut of energy the brain uses. Adiposity rebound is when the body starts to gain weight in later childhood. At this time, the amount of power the developing brain needs is reduced.

In the study published in the journal PNAS, the researchers investigated whether the way our brain develops poses a risk for excess weight gain, alongside well-explored factors such as diet and exercise.

According to the authors, most newborns have a relatively large amount of body fat, but the percentage of body weight made up of this substance starts to drop away between the ages of 3-8 years old. Humans are their leanest in early childhood, generally between 4 to 7 years of age, before the adiposity rebound happens. At around 5 years old, the brain takes up around 43 percent of daily energy requirements; that's two to three times higher than the adult brain.

Changes in how much energy an individual child's brain uses at this energy-gobbling peak, how long it lasts and when it starts and stops could change how much energy is burned and how their body composition changes with age, the authors argue.

The huge chunk of energy the brain uses might explain why humans gain weight 30 to 100 times slower in childhood than non primate mammals of a similar size, and puts us in line with cold-blooded reptiles.

The authors back their hypothesis using existing research on brain scans and genetic imaging which suggest there is a trade-off between when a child's body mass index (BMI) increases and the volume of the cortical and subcortical structures of their brain. As the BMI goes up, the amount of cognitive functions which need a lot of energy go down.

If true, this could mean programs which use a lot of brain power could help to prevent obesity, the researchers believe. The hypothesis could also explain why some children who have problems with executive functions which help us to plan have higher BMIs.

Study co-author Christopher Kuzawa, Professor at the Institute for Policy Research, Northwestern University, commented in a statement that it is widely known that the amount of energy a body burns is an important influence on weight gain.

"When kids are 5, their brains use almost half of their bodies' energy. And yet, we have no idea how much the brain's energy expenditure varies between kids," said Kuzawa. "This is a huge hole in our understanding of energy expenditure.

"We believe it plausible that increased energy expenditure by the brain could be an unanticipated benefit to early child development programs, which, of course, have many other demonstrated benefits. That would be a great win-win."

Kuzawa said a "major aim" of the paper is bringing attention to how little is known about the role of brain energy and body weight, and to encourage other researchers to measure brain energy in studies about child development "especially those focused on understanding weight gain and obesity risk."

According to the latest figures released by the CDC for 2015 to 2016, around 13.7 million children and adolescents in the U.S. are obese—or 18.5 percent. Worldwide, more than 250 million children were overweight or obese in 2016.

The CDC states that eating high-calorie, low-nutrient food and drink isn't the only factor that causes obesity in children, but also their environment, such as what their parents or schools give them to eat.

The agency warns that a child who is obese is more likely to have risk factors for cardiovascular disease and type 2 diabetes, as well as breathing problems, discomfort in their joints, and psychological issues like anxiety and depression.