The proposed project is based on the observation that schizophrenia is characterized by a chronic pro-inflammatory state, which contributes to the severity of a number of the clinical manifestations of the illness, including cognitive impairments, the treatment of which represents a critically important unmet therapeutic need.

The investigators hypothesize that the level of inflammation in people with schizophrenia can be reduced through the use of the prebiotic: Prebiotin®, an oligofructose-enriched inulin (OEI), to stimulate the activity of butyrate-producing bacteria and increase the production of butyrate, which has multiple anti-inflammatory properties. The investigators will confirm the effect of prebiotic administration on the biological signature and examine whether increased serum butyrate levels are associated with changes in cognitive performance (primary specific aim), symptoms, and metabolic measures; and the extent to which these associations are mediated by the anti-inflammatory properties of butyrate, including the ability of butyrate to decrease gut permeability and inhibit the production of pro-inflammatory cytokines, and/or changes in gut microbiota composition.

In a sample of participants with a DSM-5 diagnosis of schizophrenia or schizoaffective disorder, the investigators will conduct a 12-week, double-blind, placebo-controlled, randomized clinical trial to confirm the effect of prebiotic administration on the biological signature and examine whether increased serum butyrate levels are associated with changes in cognitive performance, symptoms, and metabolic measures; and the extent to which these associations are mediated by the anti-inflammatory properties of butyrate, including the ability of butyrate to decrease gut permeability and inhibit the production of pro-inflammatory cytokines, and/or changes in gut microbiota composition.

Inclusion Criteria:

1. DSM-5 diagnosis of schizophrenia or schizoaffective disorder;
2. Age 18-60 years;
3. Considered clinically stable by the treating psychiatrist;
4. Currently treated with an antipsychotic, with no dose changes in last 14 days;
5. Ability to participate in the informed consent process, as determined by a score of 10 or greater on the Evaluation to Sign Consent;
6. BMI ≤ 40

Exclusion Criteria:

1. Gastrointestinal disorders, including, but not limited to Crohn's Disease, Irritable Bowel Syndrome, Celiac Disease, whose pathology or treatment could alter the presentation or treatment of schizophrenia or significantly increase the risk associated with the proposed treatment protocol
2. Organic brain disorder, including cerebrovascular accident; epilepsy; traumatic brain injury, Loss of consciousness (LOC) for more than 30 minutes
3. Intellectual disability
4. Acute antibiotic use
5. Immune therapy within the last three months
6. Prebiotic or probiotic treatment within the last three months
7. Inability to understand English
8. Inability to cooperate with study procedures
9. Pregnant or lactation secondary to pregnancy
10. Participants who meet DSM 5 criteria for alcohol or substance misuse (except caffeine and nicotine) within the last 3 months will be excluded. Participants who meet DSM 5 criteria for marijuana misuse - mild will be included in the study.