A dietary intervention trial will be performed on patients affected by Behçet's syndrome. Three different diets will be compared, analyzing their effects on the gut microbiota composition, on endogenous butyrate production and on the general symptoms in Behçet's patients.

A dietary intervention trial will be conducted with the use of three different diets in order to compare the effects of these diets on the gut microbiota composition, on endogenous butyrate production and on the general symptoms in Behçet's patients.

The study will be a randomized, open trial designed to test whether a vegetarian diet or an habitual diet supplemented with oral butyrate would benefit the butyrate production, the gut microbiota composition and the general symptoms of Behçet's patients, compared with the habitual diet.

The study will involve 30 subjects with Behçet syndrome. Patients will be randomly assigned to follow a 3-months isocaloric dietary profile with either:

• vegetarian diet containing inulin and resistant starch-rich foods, including no meat and fish, but containing eggs and dairy products
• habitual diet supplemented with 2.4g/day of oral butyrate
• habitual diet without supplementation At the baseline visit, subjects will be educated about the aims and methods of the clinical trial and will sign their informed consent form.

Anthropometric measurements, body composition, and blood and stool sampling will be obtained from each participant at the beginning and at the end of the intervention period. All subjects will be examined between 07.00 and 09.30 hours after a 12 h fasting period.

The following parameters will be analyzed both at the beginning and at the end of the intervention period:

• Complete blood count
• Lipid variables - total cholesterol, low density lipoprotein cholesterol (LDL), high density lipoprotein cholesterol (HDL), triglycerides
• Glycemic profile - glucose, insulin, glycated hemoglobin (HbA1C), HOMA index
• Liver function tests - aspartate aminotransferase (AST), alanine transaminase (ALT), gammaglutamyl transferase (GGT), alkaline phosphatase (ALP), albumin, prealbumin
• Kidney function tests - serum creatinine, urea, uric acid
• Mineral profile - sodium, potassium, magnesium, calcium
• Iron metabolism - iron, ferritin
• Vitamin profile - vitamin B12, folic acid, vitamin D
• Thyroid function - TSH
• Inflammatory markers - erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), fibrinogen, serum amyloid A (SAA)
• Serology for celiac disease - IgA, anti-transglutaminase antibodies (IgA), anti endomysium antibodies (IgA)
• Circulating levels of inflammatory cytokines
• Oxidative stress markers
• Gut microbiota composition
• Butyrate production

At the beginning and at the end of the intervention period, participants will be asked to complete a questionnaire, which will assess Behçet's symptoms frequency and severity. In addition, participants will be contacted by phone to complete a 24-hours recall in order to test the adherence to diets they have been assigned to.

Inclusion Criteria:

• All patients affected by Behçet's disease

Exclusion Criteria:

• Pregnancy or breastfeeding
• Presence of diabetes mellitus
• Presence of other immune-mediated diseases
• Presence or history of cancer in the last 5 years
• Presence of infectious diseases in the last 3 months
• No antibiotic therapy in the last 3 months
• No vegetarian or vegan diet
• No intake of pro- or pre-biotics in the last 3 months

IPD will not be shared