ABSTRACT This application proposes a pilot feasibility randomized trial of the USDA Healthy Mediterranean-style Food Pattern versus standardized guidance on fiber intake for patients with diverticulitis in response to PAS-20-160, Small R01s for Clinical Trials Targeting Diseases within the Mission of NIDDK. Diverticulitis is one of the most common gastrointestinal indications for inpatient hospital admission, outpatient clinic and emergency room visits, and colon surgery. At least 20% of individuals with an initial episode of diverticulitis will have one or more painful and unpredictable recurrences. Unfortunately, there is no proven pharmacologic means to decrease the risk of diverticulitis. Large, prospective, observational studies have identified diet and lifestyle risk factors for incident diverticulitis. In one study, men who adhered to a low-risk profile (< 51g/day red meat, >23g/day fiber, 2 hours exercise/week, normal BMI, and never smoked) were 75% less likely to develop incident diverticulitis. However, these modifiable risk factors have not been evaluated for secondary prevention. Studies of diet and plasma inflammatory markers suggest that chronic, systemic inflammation is a potential mechanism that underlies the dietary effects on diverticulitis development. The Mediterranean diet pattern is comparable to diets associated with primary prevention of diverticulitis, is more strongly associated with reduced inflammation, and is familiar to providers and many patients. Thus, we propose to conduct a randomized trial (n=75) of a USDA Healthy Med- style Food Pattern versus standardized guidance on fiber intake for patients with diverticulitis to evaluate the feasibility of this dietary intervention including willingness to randomize and adherence to a Med-style dietary pattern. We will employ state-of-the-art behavioral interventions in the form of electronic feedback to improve health-related behaviors and support dietary customization based on participant’s budget, dietary preferences, and restrictions. We will also examine plasma inflammatory biomarkers (interleukin-6, interleukin-10, and interleukin-1β) and fecal calprotectin at baseline, 6, and 12 months. The proposed feasibility trial will set the groundwork for a large multicenter RCT of a food pattern–behavioral intervention versus standardized guidance on fiber intake in patients with a history of diverticulitis. It will also expand our knowledge of inflammation and diverticulitis pathogenesis and gather prospectively collected samples for future biomarker study. Ultimately, given the prevalence and morbidity of diverticulitis and the lack of predictive and preventative measures, identifying a proven means of secondary prevention and a biomarker of risk would change treatment paradigms and improve the lives of millions of patients with diverticulitis.