Diverticular Disease (DD) is a frequent condition in Western populations and may be associated with complications including bleeding, perforation, acute diverticulitis, and colon strictures. Severity of diverticular disease and its association with prognosis in relation to surgery using the Diverticular Inflammation and Complication Assessment (DICA) classification has been validated in several studies. A sedentary lifestyle, poor fibre intake and other unhealthy dietary habits have been associated with DD. On the contrary, the Mediterranean Diet (MD), which involves factors such as consuming locally grown food products, family meals, conviviality, involvement in the preparation of meals, as well as high intake of vegetables, legumes, fruit and cereals, medium intake of fish, low intake of meat and saturated fat, high intake of unsaturated fat (particularly olive oil), a medium-low intake of dairy products (yogurt and cheese), and a moderate intake of wine, seems to protect against DD. Moreover, populations that follow the MD pattern show a 50% lower rate of cardiovascular mortality due to cardiovascular disease and show highest longevity. A common finding in clinical practice is that a majority of patients undergoing a new diet stop to correctly follow the diet in the long term, suggesting the importance of periodic counselling for patients.

The aim of the study is to evaluate the impact of MD on DD and on severity of DD, and to explore the impact of incorporating a dietitian-driven counselling program in this condition.

The investigators will verify whether a 12-week nutritional intervention is able to reduce DD-related symptoms, improve patient's quality of life and reduce the need for medication. DD severity will be assessed using DICA, MD adherence will be assessed with Medi-Lite (Mediterranean Literature scoring system), symptoms will be assessed with a VAS (visual analogue scale) questionnaire and IBS-SSS (the irritable bowel syndrome severity scoring system), nutritional status will be evaluated using BIA (bioelectrical impedance analysis) and metabolic blood parameters.

Inclusion Criteria:

• Have given written informed consent to participate
• Diagnosis of SUDD defined as the presence of symptoms (mainly abdominal pain, but also constipation, diarrhea and bloating) in patients with a previous diagnosis of diverticular disease at colonoscopy in the absence of any current complications (stenoses, abscesses, fistulas)
• DICA assessment during a colonoscopy

Exclusion Criteria:

• Acute or complicated diverticulitis
• Hospitalized patients
• Patients with active oncological diseases.
• Former partial or total colonic resection or other surgical procedures for DD
• Short bowel syndrome or active perianal fistulas
• Female patients who are pregnant or breastfeeding
• Patients with known malabsorption diseases (e.g. celiac disease)
• Any unstable or uncontrolled cardiovascular, pulmonary, hepatic, renal, gastrointestinal, genitourinary, hematological, coagulation, immunological, endocrine/metabolic, or other medical disorder that, in the opinion of the investigator, would confound the study results or compromise patient safety
• Any surgical procedure requiring general anesthesia within 30 days prior to enrollment or is planning to undergo major surgery during the study period
• Patients undergoing a specific diet (e.g. diet for diabetics)
• Patients with known and well-established food allergies or intolerance to dietary elements of MD
• Patients with recent diagnosis of or non-controlled lactose intolerance
• Active participation in other interventional or drug research projects in the study period.

Individual participant data must be submitted to local Ethical Committee