Association Between Elevated Body Mass Index and Pre-frontal Lobe Functions in Healthy Adults

Introduction

Over the last decade, a growing body of evidence indicates that increased adiposity is associated with decreased brain metabolism and cognitive performance in regions associated with executive function and attention.¹ Approximately 50% of the global adult population is overweight or obese according to 2016 estimates, creating obesity pandemic.² Excess weight is a leading preventable cause of death and is associated with increased risk for cardiovascular disease and diabetes.³ There is a growing evidence that obesity is also associated with adverse neurocognitive outcome.⁴ The adverse influence of obesity on cognitive performance is also evidenced by higher rates of attention-deficit hyperactivity disorder, Alzheimer’s disease, cortical atrophy, and white matter disease in obese subjects.⁵

Elevated body mass index (BMI) has been associated with biomarkers for myelin abnormalities in the frontal lobe of healthy adults and is also related to many pathophysiologic changes with the potential to negatively impact cognitive functioning, including vascular changes, impaired insulin regulation, systemic inflammation, and reduced cardiovascular fitness.^1,4 A high BMI was linked to significant decrease in grey matter volume in locations such as the frontal lobe, bilateral medial temporal lobes, anterior lobe of the cerebellum, and occipital lobe in a study of 1,428 Japanese men utilizing magnetic resonance imaging.⁵ Volkow (2009)⁶ found inverse correlation of high BMI with metabolic activity in the prefrontal cortex and anterior cingulate gyrus using positron emission tomography in healthy adults.

Elevated body mass index has been associated with reduced cognitive performance in community samples of older adults, middle-aged adults, and young adults, specifically in the areas of memory and executive function. Studies on community-dwelling adults have found decision-making impairments to be positively associated with higher BMI’s.⁷ The link between excess weight and structural variations in the brain is not restricted to the elderly. On tests of executive function, working memory, and memory, middle-aged obese persons showed cognitive deficiencies. Such findings raise the possibility of obese, middle-aged, and young adults showing morphometric differences in comparison to their normal weight counterparts.³

A cross-sectional study investigated the correlation between BMI and global brain volume in middle-aged men and women, using magnetic resonance (MR) imaging, and reported that, elevated BMI was associated with reduced global brain volume.^8,5 Rates of attention deficit hyperactivity disorder (ADHD) were elevated in obese individuals and impulsivity was linked to BMI in some populations.⁹ Many aspects of executive functioning appears to have a direct bearing on the ability to maintain energy balance, including impulse control, self-monitoring, and goal-directed behavior.¹⁰ However, it is possible that people with poor executive function are more likely to become overweight or obese.⁴

Obesity and frontal lobe dysregulation may result in reduced focus and increased impulsivity, as well as reductions in executive function. Working memory, verbal fluency, and memory issues are common in middle-aged and older adults, and this has an impact on their social and working environments. This research aimed to identify a relationship between elevated BMI and pre-frontal lobe function (attention and executive function) performance in overweight adults and obese persons in order to improve specific neuropsychological performance.

Methods

Study design

This cross-sectional study was conducted including 73 respondents from Mangalore and its borderline cities. Authorization and ethical approval were obtained from Institutional Ethical Committee. The subjects participating in this study were given a patient information sheet containing the study details and informed consent was obtained from the subjects before the study.

Participants

Participants were selected using purposive sampling method. The eligibility criteria included healthy individuals with a minimum of high school education, both males and females aged between 30 to 45 years, with BMI greater than 24.9 (overweight and obese), and an ability to communicate. The exclusion criteria included known cases of medical and psychiatric conditions with the potential to influence cognitive performance, any history of or present traumatic brain injury or neurologic disorder, subjects with family history of ADHD, schizophrenia, bipolar disorder, or genetic disorder, current or past drug or alcohol abuse and any history of hypertension and diabetes mellitus.

Outcome measures

The data was collected using the demographic form and Saint Louis University Mental Status Scale. The demographic form included patient’s gender, age, education level, height, and weight. Quetelet’s Index was used to measure the BMI and WHO criteria were used to classify the status of body composition. Participants were assessed for pre-frontal lobe functions in order to find the association with elevated BMI using Saint’s Louis University Mental Status Scale (SLUMS). The SLUMS is a 30-point, 11-question assessment tool that assesses orientation, memory, attention, and executive function. Scores range from 0 to 30. Scores of 27 to 30 are considered normal in a high school graduate. A minor neurocognitive problem is indicated by a score of 21 to 26. Dementia is indicated by a score of 0 to 20. Data was analyzed using SPSS v 20.20 version. Karl’s Pearson’s correlation coefficient was used to find the association between elevated BMI and pre-frontal lobe function.

Results

This study included a total of 73 healthy adults. The average age of the participants in the study was 37.86 years, with a standard deviation of 4.4 years (Table 1). Majority of the study participants were males (51%), followed by females (49%) (Figure 1).

Elevated BMI was associated with impaired pre-frontal lobe function and a significant prevalence of cognitive impairment among all subjects. The correlation coefficient test developed by Karl Pearson revealed a strong negative connection (r= -0.250) between BMI and SLUMS (Table 2), as the study found that people with an elevated BMI had poor pre-frontal lobe function; it was discovered to be statistically significant (p=<0.05).

Discussion

The increased availability of high-caloric food and the reduction in physical activity seem the most important factors contributing to overweight and obesity. This study explored in a sample of 73 elderly subjects, the association between BMI and pre-frontal lobe functions. The main finding was that elevated BMI (overweight and obesity) was associated with poorer frontal lobe functions. Arnoldussen (2019)² conducted a study to determine if adiposity was cross-sectionally associated in adults with Cerebral Small Vessel Disease (CSVD). Study showed that overweight and obesity in men with CSVD, were associated with lower brain volumes. Another study demonstrated that obese individuals have smaller whole brain volume and total gray matter volume than normal weight and overweight individuals.³

Many neuropsychological tests revealed that extremely obese people performed poorly. The current study findings show that obese people have deficits in specific neuropsychological measures, such as executive skills. Previous research has also suggested a relationship between obesity-related co-morbidities (such as hypertension, diabetes, and obstructive sleep apnea) and poor cognitive performance. Although it is difficult to pinpoint the particular association between obesity and cognitive performance, high BMI is connected with various disorders, which in turn influences brain functioning.¹¹ However, there is some evidence that obesity is an independent contributor to both general cognitive functioning and executive dysfunction.¹² Furthermore, Gorospe & Dave stated that an increase in BMI was linked to an increased risk of dementia.¹³

We included only healthy adults in overweight and obese category in this study, but earlier research has shown that there is a link between medical co-morbidities, cognitive dysfunction, and patient performance in executive functioning tests. Increased BMI was associated with poorer cognitive flexibility in a paper and pencil version of the stroop paradigm in adolescents. The causes for the association between obesity and cognitive dysfunction are unknown, but there are speculative explanations. First, because a greater body mass need greater blood flow for proper functioning, it is likely that the brain is deprived of blood flow that it would typically receive in smaller bodies. As a result, a reduction of essential blood flow in those with a greater BMI could be a contributing factor for poorer cognitive performance. Alternatively, adipocytes, which were formerly considered to simply store fat, are now recognized to emit substances (e.g., cytokines, leptin) that might affect cognitive function when present in excessive amounts. Following a review of previous evidence, we discovered that people with a high BMI had poorer cognitive flexibility, which matched the current study hypothesis.¹⁴

The current study contributes to the evidence that having a high BMI is associated with poor executive function performance and shows that this pattern can be found in mostly healthy persons. More research is needed to clarify the directionality of the association between obesity and executive dysfunction, as well as to compare pre-frontal lobe performance before and after major weight loss. Such research may also offer crucial insights for effective weight loss treatment, as well as for improving mental and physical health and quality of life.

The shortcoming of the present study was that it only looked at individuals with high BMIs; therefore, no comparisons with people with low BMIs were conducted. There was no distinction between the genders.

Conclusion

Ultimately, this study found a link between BMI and pre-frontal brain functions in 73 healthy subjects. The current study found that subjects with a high BMI have a decline in pre-frontal functioning. Our findings have significant public health implications because they show that individuals with a high BMI may be at a higher risk of future cognitive impairments.