This is a feasibility-focused, patient-level randomized trial of an intervention promoting the United States Department of Agriculture (USDA) Healthy Med-Style food pattern versus standardized guidance on fiber intake (standard educational materials related to a high-fiber diet) in patients with a history of diverticulitis. This trial will assess and address barriers to the eventual large-scale trial and lay groundwork for that trial that will focus on the risk of recurrent diverticulitis and other clinical outcomes. The investigators will also compare changes in serum and stool biomarkers of inflammation that are proximal endpoints in the causal path relating a Mediterranean diet pattern's anti-inflammatory properties and recurrence of diverticulitis.

Participants randomized to the USDA Mediterranean-style Food Pattern Arm (called Medi for all) will have access to a "toolbox" that includes education materials (e.g., food pattern tables according to daily caloric intake), recipes, grocery lists, group-based online dietary support, feedback, and reminders to encourage dietary change. Recipes and grocery lists can be individualized to a participant's food budget and preferences. Materials will be available in print and Web-based. This state-of-the art intervention will then use electronic feedback in the form of nudge messages designed to motivate participants to sustain or improve adherence to the Med-style Food Pattern. Every two weeks, participants in the intervention arm will be prompted via a digital online platform (analog also available) to complete the 14-item Mediterranean Diet Assessment Score (MEDAS) (an adapted version of the MEDAS Score previously used in the Prevencion con Dieta Mediterranea \[PREDIMED study\]) for the purpose of providing timely, individual feedback on diet adherence (not for assessing adherence to the diet pattern). The MEDAS score will be calculated via the online digital platform and ranked according to 3 cutpoints: ≤7, 8-9, or ≥10. Patients will be encouraged to achieve a score of ≥10 which is considered high adherence. The platform will then offer feedback based on the levels of self-reported adherence to the diet including self vs. peer comparisons and support resources. Nudge messages will utilize information from a baseline assessment of participants' dietary attitudes and beliefs about which food groups within a Med-style food pattern they perceive to be most within their control. Ultimately, this approach will enable us to provide participants with dietary information and services that support adherence by accounting for attitudes, norms, and perceived control. The extent of interaction with the online platform will be assessed bi-weekly; degree of adherence to the USDA Med-style food pattern; and engagement in dietician services will be assessed at quarterly intervals.

Participants randomized to the High Fiber Diet Arm will be given commonly used patient education pamphlet, describing fiber and high-fiber foods, the rationale for increasing fiber intake, and ways patients can promote greater intake. Based on prior observational studies of incident diverticulitis, at least 25 grams/day of fiber will be recommended for participants.