The primary objective of this study is to evaluate the effects of a formulation containing medium-chain triglycerides (MCTs) and vegetable fibers on the quality of life of patients with psoriatic arthritis, by monitoring the patients over a period of 3 months in a single-center interventional study. As secondary objectives, the study will assess the effects of the same formulation on disease activity and on certain blood parameters and dietary habits.

The diagnostic and therapeutic framework in the field of psoriatic arthritis (PsA) is complex and not yet fully defined. Despite significant advances in pharmacological therapy and although particularly satisfactory results can be achieved thanks to new-generation DMARDs (disease-modifying antirheumatic drugs), there is still a significant gap regarding factors that, in addition to pharmacological therapy, could help patients further improve their health status, primarily dietary habits.

The aim of this study is to evaluate the effectiveness of a special medical food based on MCTs and fiber in improving quantitative and qualitative parameters in patients with PsA under stable pharmacological treatment and with low disease activity. Specifically, this will be achieved through the analysis of health-related quality of life as perceived by patients, the impact of the disease on general life, body composition and sarcopenia, physical and mental health status of patients, dietary habits, and through an evaluation of metabolic and inflammatory blood parameters.

Inclusion Criteria:

• Adult patients: aged 18-80 years;
• Clinical diagnosis of PsA meeting the CASPAR classification criteria;
• Low disease activity (4 < DAPSA ≤ 14) at the time of recruitment;
• Under stable pharmacological treatment with disease-modifying antirheumatic drugs (DMARDs) (conventional synthetic, targeted synthetic, or biological);
• Disease duration > 6 months;
• Absence of metabolic diseases.

Exclusion Criteria:

• BMI ≥ 27 kg/m²;
• Current or desired pregnancies (confirmed by pregnancy test);
• Disease activity in remission (DAPSA ≤ 4), moderate (14 < DAPSA ≤ 28), or high (DAPSA > 28) at the time of recruitment;
• Pediatric onset of the disease (< 16 years);
• Patients on a vegan, ketogenic, or MCT-rich diet (containing MCT in supplement form or high amounts of palm or coconut oil);
• Presence of ketoacidosis/metabolic acidosis, decompensated liver cirrhosis, or medium-chain acyl-CoA dehydrogenase (MCAD) deficiency;
• Type 2 diabetes, cardiovascular diseases, hypertension, ischemic diseases, renal failure, malignant tumors, respiratory diseases, dyslipidemia, fibromyalgia, metabolic syndrome;
• Major depression;
• Gastritis, esophagitis, reflux syndrome, chronic inflammatory bowel diseases (IBD);
• Lactose intolerance.