Research Update: Dietary Modification in the Treatment of Schizophrenia Spectrum Disorders: A Systematic Review

The following article summarizes the research conducted by Aucoin et al. titled Dietary modification in the treatment of schizophrenia spectrum disorders: A systematic review, which was published in the World Journal of Psychiatry in 2020.

Background

Nutritional psychiatry, a growing and fascinating area of research, examines how dietary changes can help improve the lives of people with mental health conditions. Studies have demonstrated the benefits of dietary interventions on patients with major depression; (3)(4)(6) however, limited research exists on the use of nutritional psychiatry in other mental health conditions, such as schizophrenia spectrum disorders (SSD). Nutritional guidelines exist for the management of physical comorbidities in patients with schizophrenia, such as obesity, (2)(5) but not for mental health outcomes. Fortunately, researchers from the Canadian College of Naturopathic Medicine and McGill University collaborated to conduct the first systematic review on this topic.

Adjunctive dietary interventions may help improve mental health symptoms in patients with schizophrenia spectrum disorders.

Methods

The Embase, Classic, and Ovid MEDLINE databases were searched for experimental studies assessing mental health outcomes that either altered dietary patterns or provided nutritional education to patients. Outcome measures included cognitive symptoms, levels of the biomarker brain-derived neurotrophic factor (BDNF), quality of life, psychosis symptoms, self-esteem, mental health and everyday functioning, and mental healthcare service utilization. After screening and eliminating duplicates, the initial search yielded 76,889 results, and 27 articles met the inclusion criteria. 25 of these were clinical trials and two were meta-analyses. Studies included in this systematic review used diet as an adjunct to other treatments, such as medication and counseling.

Results

While adjunctive diet interventions were found to benefit mental health outcomes in a majority of the studies, the research was mixed, with few studies reporting no effect or poorer outcomes. 21 out of the 27 research articles reported improvement in at least one mental health outcome, including improvements in quality of life, psychosis, mental health and everyday functioning, and/or cognition, as well as decreased mental healthcare utilization. Most of the interventions involved nutritional education on healthy diets and were group-based. Some interventions focused more on specific macronutrient recommendations, while others emphasized concepts such as meal planning and goal-setting. A couple of other studies had interventions that involved energy-restricted diets or education about calories. Overall, there was a high level of heterogeneity amongst the studies with respect to the patient population, intervention, and study design. In contrast to the studies reporting benefits, few studies found no effect or worsening mental health outcomes in response to the interventions. Interestingly, the studies that had better research methodology (i.e., had 200 or more participants, involved a control group or randomization), were more likely to report no benefit; however, these studies included subjects with other diagnoses and used a one-on-one intervention as opposed to a group intervention. The authors suggested that these mixed results could be due to different dietary interventions, unclear participant compliance, and variability in participant populations. Many of the studies included in the systematic review also examined physical outcomes in response to dietary and educational interventions. Studies that demonstrated improvements in physical outcomes (e.g., body mass index (BMI), waist circumference, and body weight) also tended to show benefit in mental health outcomes.

Critical analysis

This systematic review was valuable for capturing the available research on the topic of dietary modification in SSD, as the authors conducted an extensive search with few inclusion restrictions. Another strength of this review is that the findings appear to be directly applicable to people with SSD, as the studies that found adjunctive dietary interventions beneficial were less likely to include other patient populations (non-SSD). This systematic review also identified many limitations and gaps in the literature. One of the most significant limitations was that many studies had confounding variables, as they implemented other interventions alongside the dietary changes. These interventions included other lifestyle changes, such as exercise, smoking cessation, peer support, and motivational interviewing. This may make it challenging to determine the benefits of dietary interventions without changes to other health behaviors. Another limitation was that dietary interventions were poorly described, which may make replicability challenging. While some studies described goals such as increased vegetable intake and decreased saturated fat consumption, the majority of studies did not. 19 of the studies described their intervention as “a healthy diet” or “nutrition education.” The authors highlighted that this is problematic because the studies were conducted at various points in time and the definition of what constitutes a healthy diet has significantly changed over time. Additionally, most studies were conducted on adults; therefore, they have limited generalizability to other age groups. Furthermore, many of the studies were of poor methodological quality and design. With respect to methodology, many studies lacked blinding, randomization, and a control group. The studies that tended to show benefit had smaller sample sizes and were less likely to be randomized. Many studies did not monitor participant compliance, their food intake, or long-term outcomes.

The bottom line

Adjunctive nutritional interventions are low in cost and risk and can improve mental health outcomes as well as physical health parameters in patients with SSD. Although implementing dietary changes in patients with SSD can be challenging, such interventions were shown to be feasible. However, limitations of existing research hinder the ability to draw clear conclusions as to whether dietary interventions improve mental health outcomes in patients with SSD and which dietary characteristics specifically may be most effective. More controlled studies with rigorous methodology and design are needed to further establish the role of dietary interventions in the care of patients with SSD.