When we see a ketogenic diet used for decades to treat a brain disorder, some guy and his daughter see improvements in depression and other mental stuff, the late Seth Roberts finding a measurable effect of dietary fat on his cognitive performance, the famous brain fog that lifts when we all initially went low-carb (especially once we cut out the wheat), all the psycho-active drugs and medicine we consume orally, and the mental effects of certain deficiencies like scurvy and B12 for example, we can safely conclude that the stuff we eat has a definite effect on our brain functions.