The aim of this study is to determine the metabolic impact of a nutrition education program on metabolic parameters and the presence of metabolic syndrome (MetS). Seventy-four patients were included (mean age, 48.7 years Standard deviation, SD: 10.8, 55.4% men). The diagnoses of SMD were 37.8% schizophrenia and related disorders; 29.7% bipolar disorder; 25.7% depressive disorder; 4.1% personality disorders; and 2.7% obsessive compulsive disorders. Thirty-seven individuals were distributed in both the intervention group (IG) and the control group (CG). In the IG the presence of MetS was 56.3% and in the CG 46.7%, with no statistically significant difference (p = 0.309). At the end of the study, glomerular filtrate decreased in the IG, body mass index and abdominal perimeter increased in both groups, and there were no changes in metabolic parameters between the groups. Between the baseline and the end of the study, there was no increase in the number of patients diagnosed with MetS (14 at both points); and in the CG the increase was from 8 to 12 (p = 0.005). An intervention based on fruit and vegetable intake could prevent progression to MetS in individuals with SMD, decreasing the likelihood of cardiovascular disease. Trial registration The trial was retrospectively registered on International Standard Randomised Controlled Trial Number (ISRCTN) Register on 11 March 2022 (ISRCTN12024347).