A study to be published in the journal NeuroImage implies that fat people have, well, fat brains. The study is:
“Brain abnormalities in human obesity: A voxel-based morphometric study,” Nicola Pannacciulli, et al., NeuroImage, 2006, doi:10.1016/j.neuroimage.2006.01.047.
The researchers are based in Phoenix, Arizona.