Today’s post comes from Joyla Furlano. Joyla is a PhD Student in the Schulich School of Medicine and Dentistry, Neuroscience program at the University of Western Ontario. She is also the current Recruitment Coordinator of the OC-SNP National Executive.
Alzheimer’s disease is the most prevalent neurodegenerative disease and is associated with a progressive decline in cognitive function . One risk factor for Alzheimer’s disease is adiposity (obesity) . Recent research suggests that increased adiposity is associated with deficits in attention, verbal and visual memory, and decision making . Moreover, studies have found that these cognitive deficits are linked to changes in brain morphology and function . In this article, I will discuss 1) the differences in cognitive deficits experienced in obesity across the lifespan, highlighting key differences in later stages of life, and 2) the possible underlying neural changes that accompany such cognitive deficits.
A relatively consistent research finding is that obesity (commonly measured through body mass index; BMI) is associated with deficits in cognitive function in early-to-mid stages of life (i.e., childhood, adolescence, and adulthood) . Interestingly, however, studies on obesity and cognitive function in older adults (60+) show conflicting results; while some studies show a detrimental effect of high BMI on cognition, others have actually observed beneficial effects of high BMI. For example, Benito-León and colleagues found that overweight and obese older adults perform poorer on various cognitive tests compared to healthy controls , while Nilsson and colleagues found that high BMI in later life may actually be neuroprotective . Evidently, more research on cognitive function in obesity across the lifespan is needed. It is also important to highlight that differences across studies may be a result of varying sample sizes and analytical approaches, among other limitations.
In addition, research has found that obese individuals also experience deficits in brain structure and function. Raji and colleagues found that obese adults have reduced gray matter volume in areas of the brain responsible for memory and executive functions, such as the hippocampus and prefrontal cortex . Similar studies have also found reduced grey and white matter volume in other brain regions such as the hypothalamus, basal ganglia, and brainstem, all of which play an important role in the regulation of bodily functions . Given that normal aging is also associated with decreased gray and white matter volume  these findings suggest that obesity may accelerate natural age-related brain decline . Additionally, neuroimaging studies have found negative changes in neural activation patterns and functional connectivity in obese individuals compared to healthy controls , of which may underlie cognitive deficits experienced.
Taken together, the literature suggests that obesity is associated with both cognitive and brain deficits. Despite some studies suggesting that obesity may have neuroprotective benefits later in life, more research in this area is needed as there remains conflicting evidence. Future research may also consider addressing the direction of the relationship between obesity and brain/cognitive deficits; whether associations between obesity, brain deficits, and cognitive dysfunction are a consequence of weight gain or are the cause of behaviours that may subsequently lead to weight gain, for example, remains a matter of debate .
 What is Alzheimer’s? Alzheimer’s Association.  Alford et al., (2018), Obes Rev.  Prickett et al., (2015), Obes Res Clin Pract.  Stillman et al., (2017), Front Aging Neurosci. Bischof et al., (2017), Psychosom Med.  Benito-León et al., (2013), Eur J Neurol.  Nilsson et al., (2009), Scand J Psychol.  Raji et al., (2009), Hum Brain Mapp.  Bennett et al., (2010), Hum Brain Mapp.