As the train of obesity continues to surge forward and the emerging generations now sport the worst statistics of obesity prevalence and associated health implications, researchers also continue to forge ahead to identify causes and contributing factors of this problem. Brain energy consumption contributes to the resting metabolic rate and daily energy requirements and therefore, may be a plausible influencer of total energy consumption and obesity risk.
A recent hypothesis published in July 2019 in the Proceedings of the National Academy of Sciences suggests that the amount of energy utilized by the brain during childhood may contribute to overall energy expenditure, reducing the risk for obesity. The report states that the brain accounts for a lifetime peak of 66% of resting metabolic rate (RMR) or 43% of daily energy requirements (DER) at ∼5 y of age” – a rate 2 to 3 times higher than the average adult brain.
Childhood seems to be a particularly influential period during which there is a close link between the energy expenditure of the brain and weight gain between birth and adolescence. Both the brain and body growth appear to trade off energy resources so that when the brain is requiring maximum energy, the body growth rate is slowed (usually during infancy). However, as childhood progresses into puberty, brain metabolism seems to decline while body growth rate increases. This inverse relationship is measured by the ratio of glucose uptake by the brain to the body’s resting metabolic rate and daily energy requirements.
Other studies have verified that the brain is a critical organ in regulating energy intake and expenditure using various mechanisms and therefore, may play a role in obesity. Both animal and human studies have shown deep brain stimulation may be used to manage obesity. When deep brain stimulation was used on morbidly obese patients who had undergone gastric bypass surgery but with unsuccessful results, it increased resting metabolic rate which decreased appetite and increased energy expenditure, resulting in modest weight loss. These positive effects diminished once stimulation ceased.
Redirecting energy requirements may not be the only explanation behind the inverse relationship between brain activity and weight. The limbic system is directly involved in hedonic and homeostatic aspects of food-seeking behaviors. The dopaminergic reward system is one mechanism by which the limbic system controls these activities. A dysregulated system can result in food addictions and cravings. Deep brain stimulation may help correct dysregulation within the neural circuits with the outcome of more regulated food-seeking behaviors. This study does support the hypothesis that the brain is vital for regulating the body’s energy requirements and appetite suggesting that higher brain activity could promote a healthier body weight.
The brain is also responsible for sensing alterations in levels of metabolic hormones (ie. Insulin) and nutrients (ie. glucose and fatty acids) and adapting its responses to maintain healthy homeostasis and weight. It will modulate energy-consuming activities such as locomotor activity, fatty acid oxidation in the skeletal muscle, and thermogenesis in adipose tissue. These activities are directly involved in obesity and weight management.
The prefrontal cortex is the primary region where dietary food choices and control are regulated. A research summary published in 2018 concluded that increased activity in the prefrontal cortex, where executive functioning occurs, resulted in greater self-regulation of food choice which reduces risks of obesity. On the other hand, decreased prefrontal activity was associated with increased food consumption and the risk of obesity. Prefrontal activity is heightened in early childhood by structured academic exercises such as language development, goal-driven activities, structured play and peer interaction, to name a few. Deficits in prefrontal cortex activity can be linked to childhood trauma, stress exposure, poverty, detachment from caregivers. A lack of prefrontal activity resulting in poor executive functioning abilities in children has been directly associated with obesity and overweight in childhood and adolescence.
The interactions between brain activity and obesity are complex, involving multiple mechanisms cooperating simultaneously. Shifts in energy demands, as well as hormonal and limbic mechanisms, are responsible for the link between decreased brain activity and obesity. As obesity continues to plague our next generation, focusing on improving brain activity is yet another way to shift the tide on this health problem.