Nutrition's effect on the brain

Many of my friends swear by “The Ultramind Solution” by Mark Hyman, MD. The author claims that eating the right foods not only improves focus, but can also cure depression, anxiety and autism. This makes my BS-meter go through the roof, but are there actually any reliable studies on this matter?

When asking “are there any reliable studies on ___” we need to specify the question to investigate.

Hyman’s info is junk IMO.

Yeah, sorry I didn’t make it clear enough. The question is: is there any compelling evidence that some nutrients (trans fats, sugar, etc) or diets (high-fat, high-protein etc) affect the cognitive function in otherwise healthy individuals?