This study purpose is to conduct a confirmatory double-blind randomized controlled trial in an inpatient setting of the effects of a tightly controlled gluten-free diet (GFD) to improve negative symptoms in people with schizophrenia or schizoaffective disorder who have antibodies to gliadin (AGA IgG). As part of the project investigators will also confirm outcomes such as cognitive symptoms, changes in peripheral and central inflammation as well as gut/blood brain barrier permeability.