Published online Aug 19, 2020. doi: 10.5498/wjp.v10.i8.187
Peer-review started: March 20, 2020
First decision: April 26, 2020
Revised: June 25, 2020
Accepted: July 19, 2020
Article in press: July 19, 2020
Published online: August 19, 2020
Schizophrenia spectrum disorders (SSD) impact functioning, reduce quality of life and increase the risk of physical illness and premature mortality. Several observational and preclinical studies suggest a role of diet in the development and progression of SSD and rigorous clinical trials designed to assess the impact of adjunctive diet interventions in patients with major depression have reported benefit.
Nutritional intervention studies aimed at decreasing body weight have demonstrated efficacy in improving metabolic outcomes; however, few studies have explored the impact of interventions designed to modify diet on mental health outcomes. Systematic review of this body of literature has not been previously conducted.
This systematic review sought to synthesize the existing experimental studies of adjunctive diet modification as an intervention in the treatment of psychotic disorders, analyze findings related to effectiveness and safety, highlight knowledge gaps and limitations, and set forward recommendations for future research studies.
An extensive a priori search strategy was developed and the databases Embase, Embase Classic, Ovid MEDLINE were searched. Screening and data extraction were completed in duplicate. Studies included in this analysis were experimental studies of an adjunctive dietary intervention (overall dietary pattern or education on dietary change) for treatment of SSD. No restrictions were placed on control groups or blinding. The studies were required to report a mental health outcome.
Twenty-five clinical trials were identified, along with two additional protocols and two meta-analyses. Of the 25 clinical trials, four employed both blinding and randomization. Five studies used a control group and randomization but no blinding while another six studies used a control group but lacked randomization and blinding. The remaining ten trials were completed with no control group. The average sample size was 171 participants and the average duration was 33 wk. The interventions consisted primarily of nutritional education; however, the nutrition advice provided to participants was poorly described overall and compliance was not assessed. All of the studies included lifestyle or psychosocial components in addition to dietary modification. Of the 27 protocols, twelve were designed with mental health symptoms as the primary outcome. A high level of heterogeneity was found with respect to patient population, intervention, and study design. Nineteen of the clinical trials reported improvement in one or more mental health domain including psychosis symptoms, cognition, and quality of life. The studies that showed benefit tended to have a smaller sample size and were less likely to be randomized but were more likely to use a group delivery intervention. Adverse events were not generally reported.
The findings of this systematic review suggest that adjunctive diet interventions may be useful in the management of mental health symptoms in SSD; however, limitations in the existing research preclude clear conclusions.
Further research assessing effectiveness and efficacy of clearly reported dietary interventions is warranted, especially those identifying mental health symptoms as their primary outcome, using rigorous methodology (control group and blinding), modifying diet in isolation from other health behaviours and assessing participant compliance.