The aim of our study is to compare the effectiveness of Mediterranean diet (MD) with the isocaloric Ketogenic diet (KD) on clinical and biochemical markers of inflammation in patients with obesity, psoriasis (PSO) and psoriatic arthritis (PsA).

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.

Inclusion Criteria:

1. age above 18 years
2. body mass index (BMI) >30 kg/m2
3. diagnosis of psoriasis and psoriatic arthritis under constant systematic treatment with biologic agents and/or synthetic disease-modifying anti-rheumatic drugs (DMARDs) for at least 3 months.
4. ΔPASI SCORE<75, with moderate or severe activity in joints ( > 3 swollen &> 3 tender joints ή DAPSA< 14).

Exclusion Criteria:

1. participation in another study
2. eGFR<60ml/min/1.73m2
3. malignancy
4. severe hepatic disorder
5. HbA1C>10%
6. use of glucagon-like-petide-1 analogues