The main objective of the study is to assess whether a dietary regimen based on the principles of the FODMAP diet, compared with the current treatment programme which does not include specific dietary recommendations, can improve pain symptoms in patients with symptomatic endometriosis and intestinal symptoms (i.e. bloating, nausea, constipation, diarrhoea and vomiting) attributable to irritable bowel syndrome, compared with a control group

Endometriosis is defined as the presence of endometrial glands and stroma outside the uterine cavity, mostly, though not exclusively, in the pelvis. It is a chronic, estrogen-dependent inflammatory condition in which ectopic foci grow and proliferate under the action of estradiol, which plays a pro-inflammatory and anti-apoptotic role.

Pelvic pain represents the most typical manifestation of endometriosis. In particular, dysmenorrhea is the most frequent symptom.

In addition to typical gynecological symptoms, gastrointestinal symptoms (i.e., bloating, nausea, constipation, diarrhea, and vomiting) affect up to 90 percent of patients with endometriosis It has been reported how a diet low in oligosaccharides, disaccharides, monosaccharides, and fermentable polyols (FODMAP diet) is superior to other dietary treatments for the treatment of symptoms associated with irritable bowel syndrome.

Short-chain polysaccharides (FODMAPs) are found in a variety of fruits, vegetables and grains. FODMAPs are poorly absorbed in the gut, and are readily fermented by bacteria.

Their osmotic actions and gas production cause distention of the intestinal lumen inducing pain and bloating in patients with visceral hypersensitivity, with secondary effects on intestinal motility.

Although hormonal therapies represent the therapeutic cornerstone of endometriosis, we hypothesize that the FODMAP diet may represent a complementary and adjuvant approach for the treatment of abdominal/pelvic algic symptoms (and particularly bowel-type symptoms), resulting in significant improvement in the quality of life of affected women.

The primary objective of the study is to evaluate whether a dietary regimen based on the principles of the FODMAP diet versus the current treatment program, which does not include specific dietary indications, can improve algic symptoms in patients with symptomatic endometriosis and the presence of bowel symptoms (i.e., bloating, nausea, constipation, diarrhea, and vomiting) referable to irritable bowel syndrome,

Eligible women will be selected among those attending the Endometriosis Clinic of the "L. Mangiagalli ", IRCCS Ca 'Granda Foundation and Ospedale Maggiore Policlinico, and will be randomized into two homogeneous groups ("intervention" and "control") (1:1): the intervention group will consist of women with symptomatic endometriosis and concomitant bowel symptoms under estro-progestin or progestin treatment, who will be asked to follow a dietary regimen based on the principles of the FODMAP diet; women in the control group will not be given specific instructions about the diet to follow.

Women will be randomized and assigned to two groups: 1) "FODMAP diet" (FD) group; 2) "usual diet" (UD) group. All patients participating in the study will undergo clinical and ultrasonographic evaluation at the beginning of the study, after 3 months and after 6 months. On these occasions, women will be routinely asked to complete some questionnaires, one on pain (a numerical rating scale, NRS), to the evaluation of gastrointestinal symptoms (NRS related to intestinal symptoms, such as abdominal bloating, nausea, constipation, diarrhea and vomiting), one on quality of life (the Short Form-12 questionnaire, SF-12), one on psychological status (the Hospital Anxiety and Depression scale, HADS), one on sexual functioning (theFemale Sexual Function Index, FSFI) and one on the global impression of change (Patients' Global Impression of Change scale, PGIC). Women will also be asked to rate the degree of satisfaction with their treatment.

Patients randomized into the intervention group will participate in an initial meeting with the dietitian during which they will receive targeted nutritional counseling. They will be provided with the dietary pattern to follow. Follow-up of the diet will include telephone follow-up 6 to 8 weeks after the start of the study, at 3 months and at 6 months to assess dietary adherence.

Inclusion Criteria:

• Age between 18 and 45 years
• BMI between 18.5 and 24.9,
• Surgical, clinical or instrumental diagnosis of endometriosis
• Presence of bowel symptoms (i.e., bloating, nausea, constipation, diarrhea, and vomiting) referable to irritable bowel syndrome, on estro-progestin or progestin treatment or in the absence of hormonal treatment

Exclusion Criteria:

• Associated conditions that may cause pelvic pain independent of the presence of endometriosis (e.g., pelvic varices and salpingitis outcomes)
• chronic inflammatory bowel disease (Crohn's disease or ulcerative rectocolitis).
• patients with obstructive uropathy, subocclusive intestinal stenosis
• complex adnexal masses or typical endometriomas greater than 5 cm in diameter.
• women who are obese (BMI ≥ 30) or underweight (BMI < 18)
• women on vegetarian-vegan dietary regimens,
• women with metabolic diseases that require specific dietary indications such as in the case of diabetes and celiac disease.