INTRODUCTION

Schizophrenia spectrum disorders (SSD) represent a cluster of severe mental illnesses, where experiencing psychotic symptoms are the most prominent feature, with a lifetime prevalence of 3% worldwide [1]. The development is suggested to be multifacto-rial, involving genetic, biological, and social factors. One of these factors, potentially contributing to SSD pathology, is a subtle pro-inflammatory status, as reflected in increased serum levels of c-reactive protein (CRP) and pro-inflammatory cytokines, which is a rather consistent finding in the literature [2–5]. This pro-inflammatory status has been reported in drug-naive patients and is most pronounced in those with high body mass index. Many food components, such as omega-3 fatty acids, components from leafy vegetables and carotene, are direct ligands for immune cells in the gut and have a lowering effect on the immune status, where as other food components, such as saturated fat, have a pro-inflammatory effect on gut-dwelling immune cells [6▪,7].

Historically, there were already researchers who believed that certain diets could treat SSD and that diets may be used instead of medication. In 1966, an association between gluten sensitivity and schizophrenia was described by Dohan [8]. He stated that wheat intake during World War II was associated with rates of hospitalization for schizophrenia in women in five different countries. Almost 15 years later, wheat intake was correlated with schizophrenia prevalence (r = 0.53, P= 0.01) across 18 countries [9]. It was claimed that eliminating gluten from a patients’ diet would treat schizophrenia.

As of yet, antipsychotic drugs are the mainstay treatment for psychotic episodes and are also often prescribed as maintenance treatment. Antipsychotics, however, frequently lead to side-effects like increased appetite and body weight, such that the medication intervenes with the energy balance system: directly by acting on hypothalamic and reward areas of the brain and/or indirectly through changes of the gut microbiota composition [10–12]. Alterations in gut microbiota composition and microbial metabolites affect brain functioning via the so called ‘gut-brain axis’ (GBA) [11]. The GBA defines bidirectional communication pathways between the gut and brain, involving the autonomic nervous system, immune system, endocrine, and enteric nervous system. Dysregulation of the GBA was previously described in this journal by Genedi et al. and a detailed description is beyond the scope of this review [13].

Another important factor contributing to poor eating habits is the negative symptoms, such as apathy and lack of energy [14]. These symptoms prevent many people with SSD from activities as groceries shopping and preparing a home-cooked meal. SSD patients have relatively low incomes. In Western countries, unhealthy food products are easily available and tend to be much cheaper than healthyones, which facilitates the purchase of unhealthy food products by low-income groups [15].

This combination of antipsychotic-stimulated overeating, negative symptoms, and poverty generate a drive to eat high-calorie and low-nutrient food, leading to vitamin deficiencies, obesity, and associated somatic comorbidity. Obesity is highly prevalent in SSD: 58.5% of the SSD patients are obese, compared to 27% in the general population [16]. Severe overweight is associated with metabolic syndrome, which is the precursor of physical diseases like type 2 diabetes and cardiovascular diseases (CVD) that have a significant effect on quality of life and mortality [17]. Mainly due to these physical comorbidities, patients with SSD have a 15–20years lower life-expectancy than that of the general population [18].

To advance our understanding of dietary habits and preferences in SSD, the current narrative review focuses on the latest scientific developments with respect to eating habits, dietary preferences and nutritional status contributing to dietary quality in SSD. Furthermore, this review sheds light on evidence for efficacy and feasibility of dietary interventions and strategies that may alleviate the consequences of SSD. 

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EATING HABITS AND DIETARY PATTERN OF SCHIZOPHRENIA SPECTRUM DISORDER PATIENTS

Nowadays, it is commonly known that a healthy and varied diet is essential to function properly and to enjoy a healthy life. A healthy dietary pattern consists of a right balance of both macro- and micro-nutrients. Macronutrients (i.e., fats, carbohydrates (starches and sugars) and proteins) provide energy and build tissue, micronutrients (i.e, vitamins and minerals) have supportive functions in the body and ensure general health. Nutritional intake is influenced by nutritional habits: the way we eat, how often, and what we eat. Recent studies investigating eating habits and dietary patterns of SSD patients are discussed below.

Eating habits including the number and type of meals consumed during the day, snacking between meals, the energy value, and nutritional intake of schizophrenia patients (n= 85) compared to healthy control (n = 70) was investigated in a Polish study [19] (see Table 1). Dietary pattern appeared to be sex-specific; interestingly, women with schizophrenia consumed three more meals a day and snacked more frequently as compared to health women, where as in men with schizophrenia an opposite tendency was observed – their diets were characterized by over 400 kcal/day lower energy intake and a lower intake of nutrients compared to healthy men [19]. Moreover, women with schizophrenia showed significantly higher energy intake of dinner meal compared to female healthy controls (364.4 ± 154.4 kcal vs. 247.8 ± 172.5 kcal, respectively) and were especially high in saturated fats and carbohydrates [19]. This sex-specific difference maybe explained by the notion that women with mental disorders claim lower self-control while consuming sweet snacks [20]. However, more research is needed to further investigate the sex-specific differences.

Table 1 - Summary table of diet studies discussed in this narrative review Authors, year Country Sample Age (years) Study aim Results Stefánska et al., 2018 [19] Poland 85 SCZ, 70 HC 18–65 Cross-sectional study to assess nutritional habits including the number and type of meals consumed during the day, snacking between meals, the energy value, and content of chosen nutrients in diets of SCZ patients. Women with SCZ consumed three more meals a day and snacked more frequently as compared to healthy women. In men with SCZ an opposite tendency was observed - their diets were characterized by lower energy intake and lower intake of nutrients compared to healthy men. Jakobsen era/., 2018 [21] Denmark 428 SCZ/SAD with increased waist circumference, 3016 individuals general Danish population 18–75 Observational cross-sectional study to investigate dietary habits and physical activity in overweight SSD and compare results with current recommendations and with result from general Danish population. The total caloric intake of the SSD patients was similar to that of the Danish general population. The distribution of fat, carbs, and protein (35% of energy from fat, 49% from carbohydrate and 16% from protein) intake matched the Danish Health Authorities’ guidelines and was similar to dietary pattern of the Danish general population. The intake of saturated fat, sugar and alcohol exceeded the recommended amounts and the corresponding intake in the general population. Intake of fibers, fruit, vegetables, and fish was insufficient and significantly lower than the general population. Overall estimated quality of the dietary habits of SSD patients was poor. The quality was poorer than in the general population. Only 62% of the SSD patients took part in the preparation of their food. Negative symptoms were found to be strongly linked to poorer nutritional quality and less physical activity. Costa et al., 2019 [23▪] Portugal 100 SCZ Mean age 44.6 A cross-sectional study to (i) assess dietary intake SCZ [comparing inpatient and outpatients; (ii) determine adherence to Mediterranean diet; (iii) explore potential relationships between the Mediterranean diet and lifestyle-related factors. SCZ patients reported a poor to moderate quality of the dietary intake. They consumed more than twice as much caffeine, compared to the EFSA recommendations. Mean fiber intake was significantly lower than recommended and there was a trend to significantly lower folate intake. Smokers reported poorer diet quality compared to nonsmokers. Firth et al, 2018 [24] UK SMI: 262 SCZ, 952 BD, 14.619 MDD 54,010 SMI-free Mean age 56.5 Population-scale study to examine differences in nutritional intake and diet-associated inflammation between people with SMIs and the general population. Intake of total energy, carbohydrates, total fat, saturated fat, and protein were highly elevated compared to HC. SCZ patients showed elevated Dll scores compared to HC. Jahrami et al., 2019 [26] Bahrain 120 SCZ, 120 HC 20–60 Case-control study to examine association between dietary inflammation and SCZ. The E-DII score was higher in SCZ patients compared to HC. Niarchou et al., 2020 [28] UK 335.576 individuals from the UK biobank study 40–69 Genome-wide association study to investigate genetic contribution to dietary intake in individuals from UK Biobank study. Slight association between SCZ and ‘fish and plant eaters’. Kelly et al., 2019 [47] USA 16 SCZ/SAD who had elevated AGA IgG |"],"an":"00001504-202205000-00008"},"eventOptions":,"loginDetail":,"isNull":false}"> Related Articles Article Level Metrics Article Keywords

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dietary pattern\r, inflammation\r, nutrient deficiency\r, schizophrenia spectrum disorders

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