Appetite Hormone May Inhibit Learning has an article which says that

leptin regulates appetite
obese people have more than the average leptin
so it seems that leptin doesn’t work for the obese


abnormal amounts of leptin alter brain cell function
which can impact everything from short term memory to Alzheimer’s.

Which means obese people may be more at risk for short term memory loss, brain cell function, and Alzheimer’s.