This clinical study is designed to evaluate the effect of two dietary patterns, Mediterranean diet and the specific carbohydrate diet on clinical, inflammatory and microbial parameters in patients after pouch surgery and to assess the effect of a personal tailored diet, based on microbial profile, on disease outcomes and generate a predictive model for future interventions.

Increasing evidence exist regarding the role of diet in the pathogenesis of inflammatory bowel diseases. One possible mechanism for the effect of diet on intestinal inflammation is modification of the gut microbial composition. However, the relationship between diet, the microbiome and intestinal inflammation is still vague.

The investigators plan to perform a crossover clinical trial. Seventy ulcerative colitis patients post restorative proctocolectomy (pouch) will be randomly allocated into two short-term (one week) dietary interventions, the Mediterranean diet and the specific carbohydrate diet, to assess which diet has the required influence (i.e. increased diversity, decrease in specific pathobionts and increase in "anti-inflammatory" taxa) on the gut microbiome of each participant. Based on this assessment, each participant will be treated by a personally-tailored diet for up to one year, during which microbial composition, clinical parameters, and quality of life will be assessed.

Inclusion Criteria:

• Patients aged 18-75;
• Able and willing to sign an informed consent;
• Underwent pouch surgery because of refractory UC or Familial Adenomatous Polyposis (FAP) and have a functioning pouch.

Exclusion Criteria:

• Patients with ileostomy, stricturing disease, use of antibiotics in the month prior to inclusion, significant comorbidity that precludes the patient from participating according to the physicians' judgment, non-Hebrew readers, pregnant and lactating women.