Obesity is a growing concern worldwide and has been linked to numerous health problems, including cognitive impairment. Research has shown that individuals with obesity tend to have poorer cognitive performance than those with normal body-mass index (BMI).
In this analysis, we will explore the significant differences in cognitive performance, brain structures, and brain circuitry between individuals with obesity and those with normal BMI.
Cognitive Performance: Several studies have found that obesity is associated with lower cognitive performance. Specifically, individuals with obesity tend to have poorer executive function, attention, memory, and processing speed compared to those with normal BMI. These cognitive deficits are likely due to alterations in brain structures and circuitry that are discussed below.
Brain Structures: Obesity has been associated with alterations in brain structures, including the hippocampus, amygdala, prefrontal cortex, and basal ganglia. These brain regions are involved in various cognitive processes, including learning and memory, emotion regulation, and executive function.
For example, the hippocampus is essential for forming and retrieving memories, and studies have found that individuals with obesity have reduced hippocampal volume, which may contribute to their memory deficits.
The prefrontal cortex is also critical for executive function, attention, and working memory, and studies have found that individuals with obesity have reduced prefrontal cortex volume and thickness. Additionally, the basal ganglia, which are involved in reward processing and motivation, have been found to be altered in individuals with obesity, which may contribute to their food-seeking behaviors and cravings.
Brain Circuitry: Obesity has also been associated with alterations in brain circuitry, including changes in the reward system, hypothalamus, and insula. The reward system, which includes the ventral striatum and orbitofrontal cortex, is involved in processing rewarding stimuli, including food, and studies have found that individuals with obesity have increased activation in this system in response to food cues.
The hypothalamus plays a critical role in regulating appetite and energy balance, and studies have found that individuals with obesity have reduced hypothalamic volume and altered hypothalamic circuitry. Additionally, the insula, which is involved in interoception and self-awareness, has been found to be altered in individuals with obesity, which may contribute to their poor food choices and lack of awareness of their body’s hunger and satiety signals.
The prevalence of obesity in children and adolescents has been increasing globally over the past few decades. Excess body weight during early childhood has been associated with several negative health outcomes, including type 2 diabetes, cardiovascular disease, and cognitive impairment. Previous studies have suggested that obesity can affect brain structure and function, which may in turn affect cognitive performance. However, the exact mechanisms by which obesity affects brain circuits and cognitive performance are not yet fully understood.
This study aimed to investigate the effects of excess BMI on brain circuits during neurodevelopmentally vulnerable periods in early adolescence. The study found that overweight and obese children exhibited alterations in functional connectivity between brain regions involved in cognitive processes, compared to normal weight children.
These alterations were mainly observed in brain regions within the default mode network (DMN), which is a set of brain regions that are active when the brain is at rest and deactivated during goal-directed tasks. The altered DMN connectivity in overweight and obese children suggests that they have difficulty disengaging from internal thoughts and attending to external stimuli during task performance, which may impair their cognitive performance.
The study also found that overweight and obese children had reduced gray matter volume in brain regions involved in cognitive control, such as the prefrontal cortex and anterior cingulate cortex, compared to normal weight children. The reduced gray matter volume in these regions is associated with poor cognitive performance and increased risk for psychiatric disorders.
These findings suggest that excess BMI during neurodevelopmentally vulnerable periods can lead to alterations in brain structure and function, which may in turn affect cognitive performance. The alterations in brain circuits observed in overweight and obese children may be due to changes in neurotransmitter function and neuroinflammation, which have been associated with obesity. The reduced gray matter volume in brain regions involved in cognitive control may be due to a decrease in neurotrophic factors, which are necessary for the survival and function of neurons.
It is important to note that the causal relationship between excess BMI and alterations in brain structure and function is not yet clear. It is possible that the alterations in brain circuits and gray matter volume observed in overweight and obese children are due to other factors that are associated with obesity, such as physical inactivity, poor nutrition, and stress.
Adverse effects of excess BMI (affecting 1 in 5 children in the US) on brain circuits during neurodevelopmentally vulnerable periods are incompletely understood. This study investigated BMI-related alterations in maturating functional networks and their underlying brain structures, and high-level cognition in early adolescence.
Cross-sectional resting-state fMRI, structural sMRI, neurocognitive task scores, and BMI from 4922 youth [median (IQR) age = 120.0 (13.0) months, 2572 females (52.25%)] from the Adolescent Brain Cognitive Development (ABCD) cohort were analyzed. Comprehensive topological and morphometric network properties were estimated from fMRI and sMRI, respectively. Cross-validated linear regression models assessed correlations with BMI. Results were reproduced across multiple fMRI datasets.
Almost 30% of youth had excess BMI, including 736 (15.0%) with overweight and 672 (13.7%) with obesity, and statistically more Black and Hispanic compared to white, Asian and non-Hispanic youth (p < 0.01). Those with obesity or overweight were less physically active, slept less than recommended, snored more frequently, and spent more time using an electronic device (p < 0.01). They also had lower topological efficiency, resilience, connectivity, connectedness and clustering in Default-Mode, dorsal attention, salience, control, limbic, and reward networks (p ≤ 0.04, Cohen’s d: 0.07-0.39). Lower cortico-thalamic efficiency and connectivity were estimated only in youth with obesity (p < 0.01, Cohen’s d: 0.09-0.19). Both groups had lower cortical thickness, volume and white matter intensity in these networks’ constituent structures, particularly anterior cingulate, entorhinal, prefrontal, and lateral occipital cortices (p < 0.01, Cohen’s d: 0.12-0.30), which also mediated inverse relationships between BMI and regional functional topologies. Youth with obesity or overweight had lower scores in a task measuring fluid reasoning – a core aspect of cognitive function, which were partially correlated with topological changes (p ≤ 0.04).
the various ways in which obesity and high BMI can impact cognitive function and brain structure :
- Inflammation: Obesity is associated with chronic low-grade inflammation, which can have negative effects on brain function. Inflammation can impair the ability of neurons to communicate with each other, disrupt neurotransmitter function, and cause damage to brain tissue. This can lead to cognitive deficits, including problems with memory, attention, and decision-making. In the context of COVID-19, obesity is also associated with a higher risk of severe disease and mortality, and inflammation is thought to play a role in the hyperinflammatory response that can occur in severe cases.
- Hormonal dysregulation: Obesity can disrupt the balance of hormones in the body, including insulin and leptin, which are important for regulating metabolism and appetite. These hormones also play a role in brain function, and disruptions in their levels can affect cognitive performance. For example, insulin resistance, a common feature of obesity, has been associated with cognitive impairment and reduced brain volume in some studies. In the context of COVID-19, obesity is also associated with an increased risk of insulin resistance and type 2 diabetes, which can further exacerbate cognitive deficits.
- Direct effects on brain structure: Obesity can impact brain structure directly. Magnetic resonance imaging (MRI) studies have found that obese individuals have reduced gray matter volume in several brain regions, including the prefrontal cortex and the hippocampus. These regions are involved in cognitive processes such as memory, attention, and decision-making. The reduction in gray matter volume in these regions may contribute to the cognitive deficits observed in obese individuals. In the context of COVID-19, there is evidence to suggest that the virus can directly infect the brain and cause neurological symptoms, and obesity may increase the risk of these effects.
- Alterations in brain network connectivity: Obesity can affect the function and connectivity of brain networks. Functional MRI (fMRI) studies have found that obese individuals exhibit altered connectivity between brain regions involved in cognitive processes, such as the default mode network (DMN). The DMN is a network of brain regions that is active during rest and deactivated during goal-directed tasks. Altered DMN connectivity in obese individuals may reflect difficulties in disengaging from internal thoughts and attending to external stimuli during task performance. In the context of COVID-19, there is evidence to suggest that the virus can cause disruptions in brain network connectivity and cognitive function, and obesity may exacerbate these effects.
Overall, the negative effects of obesity on cognitive function and brain structure can have implications for the impact of COVID-19 on the brain. Obese individuals may be at a higher risk of severe disease and mortality, as well as cognitive deficits and neurological symptoms associated with the virus. Understanding the link between obesity, COVID-19, and brain health is an important area of research, and may lead to improved interventions and treatments for both conditions.
Excess BMI in early adolescence may be associated with profound aberrant topological alterations in maturating functional circuits and underdeveloped brain structures that adversely impact core aspects of cognitive function.
reference link https://www.nature.com/articles/s41366-023-01303-7