Obesity and excess body fat in  middle age has  been shown to be correlated with Alzheimer disease later in life. Visceral fat, the fat which is found around our internal body organs is known to be associated with insulin resistance which is a proinflammatory state. Both of these are felt to be involved in the development of the pathology of Alzheimer’s Disease.

Obesity generates a chronic low-grade inflammatory state, which is known to be characteristic of a variety of chronic health problems notably the metabolic syndrome, type 2 diabetes mellitus, and cardiovascular disease [28,29]. Also chronic low grade neuroinflammation [30,31,32], is associated with the development of neurodegenerative diseases. [33,34,35].

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9912737/

Obesity has been shown to have so many effects on the body that it can be considered a multisystem disease affecting the cardiovascular system,  gastrointestinal tract, the lungs and other vital organs and functions. [1]. Excess body  weight is linked to metabolic changes which result in type 2 diabetes, abnormal lipid profiles, and high blood pressure [2]. Research has also emerged which ties obesity  to problems of  the central nervous system which may worsen cognitive abilities [3].  In a study of greater than  20,000 participants from the UK Biobank excess  body fat is correlated with diminished fluid intelligence and memory [4], which are seen as early indicators of dementia and Alzheimer’s disease (AD) [5, 6]. At this point in time enough science has been developed to consider  obesity is a risk factor for Alzeheimer’s disease [7–11]. It is felt that documentable neurodegenerative changes (seen by brain MRIs) underlie the mechanism leading to recognizable cognitive difficulties. The researchers in this field attempt to see if they can show that otherwise healthy individuals who are overweight manifest these weight-related neurodegeneration changes seen as distinct from the changes seen with aging itself. It has been long known  that excess weight is correlated with cerebrovascular disease and poor cerebral circulation [13]. The same brain changes in certain  regions of the brain are  seen in both Alzheimer’s Disease and obesity[4, 15, 16], although the changes are more severe in Alzheimer’s. These changes include degenerative  white matter changes, the presence of cerebrovascular disease and ischemia, grey matter degradation, and  accumulation of amyloid-β and tau proteins [12, 17].  It is to be determined whether the amyloid-β and tau changes are representative of risk for the development of Alzheimer’s or whether they are actually a measurable sign of impending Alheimer’s .

Magnetic resonance imaging  scans were studied measuring cortical thickness. Also it attempted to determine if the grey matter abnormalities occur in a pattern distinct to obesity. And then the question as to whether that pattern is the same as seen in Alzheimer’s disease will be answered. Study of grey matter is essential because it is there that the well defined abnormalities of Alzheimer’s Disease have been elucidated.[18, 19].

As a part of this study they looked at the study subjects who had Alzheimer’s disease and compared them to study participants of the same age and sex who were unaffected by cognition problems. Then they divided up the study subjects into those who were lean and those who were obese. They wished to see if  the brain patterns seen in Alzheimer’s Disease and in obesity D and obesity are correlated with changes in their weight status.

The following NIA funded study from Washington University in St. Louis attempted to show if abdominal obesity can be used to assess Alzheimer’s risk. They measured abdominal fat via the use of MRI studies

They analyzed BMI, insulin resistance, and brain scans from 32 , middle age adults (ages 40-60 years) who had no signs of cognitive difficulties.  MRI scans were used  to measure abdominal fat. The analysis of brain scans showed that those who scored higher on their BMI score,and abdominal obesity, as well as those with insulin resistance had a lower cortical thicknesses in the temporal lobe region of the brain as well as other areas known to show abnormalities in those with Alzheimer’s disease.

They also found that men with abdominal obesity had higher levels of the protein beta-amyloid in crucial areas of the brain known to be affected in early onset  Alzheimer’s disease. This may suggest that the association of abdominal obesity with beta-amyloid buildup and lower cortical thickness in midlife are early biomarkers, occurring before tau buildup and cognitive decline.

https://pubmed.ncbi.nlm.nih.gov/38027213/

 Previous studies have investigated changes in the cerebral cortical structure and cognitive function among patients with nonalcoholic fatty liver disease (NAFLD) . They conclude that  NAFLD is suggestively associated with atrophy in specific functional regions of the human brain.

The findings of this pilot study support the idea that abdominal obesity may be used to assess Alzheimer’s risk. The researchers plan to recruit 20 participants for the next phase of research.