Until today, the nutritional approach that would be the most efficient in the treatment of metabolic syndrome has not been defined neither in the general population nor in people diagnosed with schizophrenia. The present study aimed to determine the prevalence of metabolic syndrome and the dietary habits in hospitalized patients diagnosed with schizophrenia aged ≥ 18 years (n = 259). The overall prevalence of metabolic syndrome was 47.9 %. There were no statistically significant differences found between the participants with and without metabolic syndrome with respect to dietary habits. Several participants with metabolic syndrome (n = 79) were included in a randomized controlled trial which primary outcome was to determine the impact of the Dietary Approaches to Stop Hypertension (DASH) diet nutritional intervention on metabolic syndrome and its parameters. A total of 67 participants (n = 33 in the experimental group and n = 34 in the control group) completed a three-month study. The experimental group received meals prepared according to the principles of the DASH diet with an energy intake restriction of approximately 400 kcal/day compared to the standard hospital diet given to the control group. Both groups participated in a nutritional education program. Upon the expiry of the three months' period, the metabolic syndrome prevalence significantly decreased in both the experimental (prevalence after the intervention 75.8 %; p = 0.002) and the control group (prevalence after the intervention 67.7 %; p = 0.0003). At the end of the intervention, there were no statistically significant differences in the prevalence of metabolic syndrome and its parameters between the groups. However, although the DASH diet when compared to the standard hospital diet did not result in a statistically significant reduction of the prevalence of metabolic syndrome and its parameters, it led to significant improvements in diet quality and dietary habits of hospitalized schizophrenic patients with metabolic syndrome.