Reduced brain function and capacity, for starters, and also it seems that really fat people honestly believe that they cannot be any smaller, and since they don't understand CICO or even how the body functions at a basic level, they're lost. Add in all of the HAES and body-positivity BS that they get bombarded with, and you have a very large segment of the population practically forced into stagnation with no clear understanding of why. They cannot link their physical problems to their physical state. It must be particularly frustrating for the poor doctors that have to deal with them.