It's quite possible the brain isn't optimised for the current availability of nutrients. Judging by the number of overweight people walking around it seems like

It's quite possible the brain isn't optimised for the current availability of nutrients. Judging by the number of overweight people walking around it seems likely that evolution has selected for efficiency rather than performance. Given that our gene pool hasn't changed much in 250,000 years a little chemical nudge in the right direction is probably the way to go.