In one of the largest studies linking obesity with brain dysfunction, brain scans from more than 17,000 individuals (aged 18-94; mean age 40.8) were analyzed to measure blood flow and brain activity. Across all ages, higher BMI was associated with decreased cerebral blood flow. This was seen in almost all brain regions, and particularly so in regions known to be vulnerable to Alzheimer’s: temporal and parietal lobes, hippocampus, posterior cingulate gyrus, and precuneus.

https://www.eurekalert.org/pub_releases/2020-08/ip-bwh080520.php

Amen, Daniel G. et al. 2020. Patterns of Regional Cerebral Blood Flow as a Function of Obesity in Adults. Journal of Alzheimer’s Disease, 1 Jan. 2020: 1–7.