Overall, twenty patients with body mass index (BMI) \>30 kg/m2, PSO and PsA under constant systematic treatment for at least 3 months will be included in the study. They will randomly assign to two groups, starting either with MD or KD for a period of 8 weeks. After a 6-week washout interval, the two groups will cross over to the other type of diet for the same 8-week period. The primary endpoint is the change in Psoriasis Area and Severity Index (PASI) and the Disease Activity Index for Psoriatic Arthritis (DAPSA) score, 8 weeks after each diet intervention. Secondary endpoints are changes in biochemical markers of inflammation (IL-6, IL-17, IL-22, IL-23) , in metabolic and anthropometric parameters.
