Here's just a smattering of the studies performed over the past 30 years on the psychological effects of wheat consumption.

Oddly, this never makes the popular press. But wheat underlies schizophrenia, bipolar illness, behavioral outbursts in autism, Huntington's disease, and attention deficit hyperactivity disorder (ADHD).

The relationship is especially compelling with schizophrenia:

Opioid peptides derived from food proteins: The exorphins.
Zioudrou C et al 1979
"Wheat gluten has been implicated by Dohan and his colleagues in the etiology of schizophrenia and supporting evidence has been provided by others. Our experiments provide a plausible biochemical mechanism for such a role, in the demonstration of the conversion of gluten into peptides with potential central nerovus system actions."


Wheat gluten as a pathogenic factor in schizophrenia
Singh MM et al 1976
"Schizophrenics maintained on a cereal grain-free and milk-free diet and receiving optimal treatment with neuropleptics showed an interruption or reversal of their therapeutic progress during a period of "blind" wheat gluten challenge. The exacerbation of the disease process was not due to variations in neuroleptic doses. After termination of the gluten challenge, the course of improvement was reinstated. The observed effects seemed to be due to a primary schizophrenia-promoting effect of wheat gluten."


Demonstration of high opioid-like activity in isolated peptides from wheat gluten hydrolysates
Huebner FR et al 1984


Is schizophrenia rare if grain is rare?
Dohan FC et al 1984
"Epidemiologic studies demonstrated a strong, dose-dependent relationship between grain intake and the occurrence of schizophrenia."