Is the Energy Demand of the Developing Brain Related to Lifetime Obesity Risk? (WP-19-06)
Christopher W. Kuzawa and Clancy Blair
The causes of obesity are complex and multi-factorial. The researchers propose that one unconsidered but likely important factor is an energetic trade-off between brain development and fat deposition. Humans are leanest during early childhood and regain body fat in later childhood and adolescence. Children reaching this “adiposity rebound” (AR) early, or at higher body mass index (BMI), are at risk for adult obesity. In aggregate data, the energy demands of the developing brain reach a lifetime peak of 66% of resting energy expenditure in the years preceding the AR and are tightly, inversely related to body weight gain from infancy until puberty. Building on this finding, the authors hypothesize that individual variation in childhood brain energy expenditure will help explain variation in the timing of the AR and subsequent obesity risk. This hypothesis is consistent with evidence that genes that elevate BMI are expressed in the brain and mediate a tradeoff between the size of energetically costly brain structures and BMI. Variability in energy expended on brain development and function could also help explain widely documented inverse relationships between BMI and cognitive abilities associated with prefrontal cortex. The researchers estimate that variability in brain energetics could explain the weight differential separating children at the 50th and 70th BMI-for-age centiles immediately prior to the AR. Our model proposes a role for brain energetics as a driver of variation within a population’s BMI distribution, and suggests that early educational interventions that boost global brain energy use during childhood could help reduce the burden of obesity.