The present study was carried out to determine the dietary habits of patients with schizophrenia and the influence of these habits on the degree of obesity. The study was developed in a sample of 159 patients, who were given a self-reported questionnaire, to ascertain the influence of socio-familiar aspects, pharmacological treatment, and dietary habits. Anthropometric measurements (body mass index (BMI) and waist circumference (WC)) were also taken. Patients with schizophrenia presented unhealthy dietary habits, as indicated by the finding that 51% of the patients took no longer than 15 min to eat, 40.8% did not eat fruit daily, and 63.1% did not eat fish. Women were three times more likely to be obese than men (odds ratio (OR) = 2.91, P = 0.021). Patients classified as having unhealthy dietary habits have a 2.33-fold higher risk of obesity than patients with good dietary habits (OR = 2.33, P = 0.034). In summary, this paper highlights the fact that patients with schizophrenia have a detrimental dietary pattern that is associated with an increase in BMI and WC, with the consequent development of obesity and related metabolic alterations, regardless of the pharmacological treatment being followed. Future research directions will include exploring the need for nutritional education programmes to improve the dietary habits of such patients.