The goal of this clinical trial is to evaluate whether different dietary models can improve clinical, metabolic, hormonal, anthropometric, and quality-of-life parameters in women with polycystic ovary syndrome (PCOS).

The main questions it aims to answer are:

• Do the Mediterranean Diet and the FertilOMed Diet (Fertility-Optimized Mediterranean Diet) lead to significant improvements in these parameters compared to the control group?
• Does the FertilOMed Diet lead to greater improvements compared to the standard Mediterranean Diet? Study Description: This randomized controlled intervention study will be conducted between November 2025 and March 2026 at the Samsun Training and Research Hospital, Department of Obstetrics and Gynecology, Women's Health Outpatient Clinics. Necessary institutional permissions have been obtained for conducting the study at these sites.

Participants: Women diagnosed with PCOS who meet the inclusion criteria and volunteer to participate will be included in the study.

Interventions:

Participants will be randomly assigned to one of the following groups:

• Mediterranean Diet group
• FertilOMed Diet group (Fertility-Optimized Mediterranean Diet)
• Control group (standard dietary recommendations) Researchers will compare these groups to determine whether the dietary interventions improve clinical, biochemical, and symptomatic outcomes in women with PCOS.

This study will include volunteer female individuals who have applied to the Gynecology and Obstetrics outpatient clinic of the Gynecology and Obstetrics Department of Samsun Training and Research Hospital, diagnosed with PCOS by a physician, and selected according to inclusion and exclusion criteria. Women who meet the criteria will be informed about the study's objectives and methodology, and those who agree to participate will be asked to sign a consent form. Individuals will be assigned to control and intervention groups, matched by age and BMI. Care will be taken to ensure that the groups are matched by age and body mass index (BMI). At the beginning of the study, a questionnaire containing sociodemographic information, general health information, dietary habits, physical activity status, sleep habits, morningness-eveningness scale, PCOS-50 Quality of Life scale, Beck depression scale, SF-36 scale, and food consumption record will be administered to the individuals via face-to-face interviews by the researcher. Initial anthropometric measurements of the female volunteers will be taken by the researcher using appropriate techniques. Additionally, biochemical findings will be obtained from hospital records at the beginning and end of the study. Volunteers, matched by age and BMI, were included in the control and intervention groups and will be followed for 12 weeks. Individuals in the control group will receive only medical treatment throughout the study period. They will be free to make food choices without energy restrictions (ad libitum). No dietary intervention will be implemented. Individuals in the intervention groups will receive ad libitum nutrition education and brochures about the diet's content, in addition to their medical treatment. Individuals in both intervention groups will not be restricted in their daily dietary energy intake.

During the 12-week follow-up period, individuals will be closely monitored through mobile applications and routine follow-up visits.

Inclusion Criteria:

• Being diagnosed with PCOS according to the Rotterdam Criteria, between the ages of 20 and 45,
• Having a Body Mass Index (BMI) of 18.50-35.00 kg/m2,
• Not having used antibiotics and/or probiotics in the last month,
• Signing a voluntary consent form.

Exclusion Criteria:

• Being younger than 20 years old or older than 45 years old with PCOS diagnosis,
• Having a BMI of ≤18.50 kg/m2 and ≥35.00 kg/m2,
• Being pregnant or breastfeeding,
• Using alcohol,
• Having used antibiotics and/or probiotics in the last month,
• Having had bariatric surgery,
• Having type 1 diabetes, type 2 diabetes, Cushing's syndrome, hypothyroidism, androgen tumors, active cancer, or a gastrointestinal system or malabsorption disease,
• Having used hormonal contraceptives or insulin sensitivity-enhancing medications within 3 months before the study start,
• Having used antioxidant supplements such as vitamin C within 1 month before the study start,
• Having a Mediterranean Diet Adherence Score (MEDAS) of ≥10,
• Those who did not give their consent after reading the informed consent form.