Achieving optimal glycemic control in type 1 diabetes requires a holistic approach that includes individualized medical nutrition therapy in addition to appropriate insulin therapy. When diabetes is poorly managed, metabolic control is impaired. Hyperglycemic events increase oxidative stress in the body and can lead to complications. The aim of this study is to examine the effect of a 12-week Mediterranean diet on oxidative stress markers in children with type 1 diabetes who do not meet the metabolic target (HbA1c > 7%) and whose adherence to the Mediterranean diet is "poor" and "needs improvement".

The study, planned between March 2026 and March 2027, will be conducted with girls aged 10-18 years with type 1 diabetes who are followed up at the Department of Pediatric Endocrinology, Istanbul Faculty of Medicine, Istanbul University. In the first phase, participants were divided into groups based on their HbA1c levels: those with HbA1c ≤ 7 met the metabolic target (Group A); Those with HbA1c > 7 will be divided into two groups: those not meeting the metabolic target (Group B). In the second stage, the intervention group will be determined according to the results of the KIDMED, the pediatric Mediterranean diet adherence scale. Those in Group B who did not meet the metabolic targets and those with "poor" and "need improvement" KIDMED results will form the intervention group (Group C). Adolescents in Group C will receive a 12-week Mediterranean diet intervention. Information will be collected from participants using questionnaires, scales, and experimental methods. This includes completing the 'Personal Information Form', 'Biochemical Parameters Form', '3-Day Nutrition Questionnaire', 'KIDMED scale', and 'Sensor Data Form'. The obtained data will be analyzed both individually and before-and-after using SPSS 26.

The findings are expected to show improvement in OS markers in the intervention group. Improvement in glycemic control markers is also predicted. A decrease in HbA1c levels, a reduction in blood sugar fluctuations, and an increase in the duration of staying within the target range are expected.

This study is expected to contribute to the literature by revealing the effects of the Mediterranean diet on oxidative stress and metabolic control parameters in type 1 diabetes. It is anticipated that the findings will support the potential role of dietary approaches with antioxidant properties not only in glycemic control but also in oxidative stress levels and long-term complication risks.

Type 1 diabetes is an autoimmune disease that primarily occurs in childhood and is characterized by insufficient insulin secretion due to damage to the beta cells of the pancreas. While the incidence of Type 1 diabetes is increasing, the age of onset is also decreasing.

Diabetes management is crucial for maintaining and protecting health. When glycemic control is not achieved, the number of hypoglycemic and hyperglycemic events increases. HbA1c levels rise. This situation results in poor metabolic control. Oxidative stress in the body increases. Oxidative stress can play a role in the pathogenesis of diabetes, and if the disease is not controlled, it leads to the development and rapid progression of complications (retinopathy, nephropathy, neuropathy, etc.).

Many studies conducted on diabetic children have shown that their oxidative stress levels are high and antioxidant levels are low compared to healthy controls.

Nutrition, the foods we consume, are modifiable determinants of oxidative stress. The antioxidant and polyphenol content of the diet is particularly important. The Mediterranean diet; Foods rich in antioxidants, such as vegetables, fruits, legumes, fish, olive oil, nuts, and fermented foods, have been shown in many studies to have a protective effect.

In the first phase of the study, participants will be divided into two groups based on their HbA1c levels: those with HbA1c ≤7 (meeting the metabolic target) (Group A); and those with HbA1c >7 (not meeting the metabolic target) (Group B). Information will be collected from participants using questionnaires, scales, and experimental methods. This includes completing a Personal Information Form, a Biochemical Parameters Form, a 3-Day Food Intake Record, the KIDMED scale, and a continuous glucose monitoring sensor data form. Disease-specific information will be obtained from patient files, while biochemical data will include routine follow-up measurements such as complete blood count, CRP, CK, HbA1c%, lipid profile (HDL, LDL, total cholesterol, triglycerides), liver function tests (AST, ALT), kidney function tests (BUN, urea, creatinine), TSH, ST4, and vitamin D. Oxidative stress markers FASN, G6PD, GST, GR, and 6-PGD will be measured in venous blood. Blood samples will be taken in the outpatient clinic by a diabetes nurse. Anthropometric measurements will be taken as part of the personal information form. Body weight and height measurements will be taken in the outpatient clinic by a nutritionist (the same person). Height measurements will be taken with a stadiometer with 0.1 cm accuracy, while the patient is in an upright position with the head in the Frankfort plane (the ear canal and the lower boundary of the orbit/eye socket are aligned, and the gaze is parallel to the ground). Body weight measurements will be taken with a scale with 0.1 gram accuracy. Anthropometric data (body mass index, weight, height, and standard deviation scores) will be evaluated according to the standards developed by Neyzi et al. for Turkish children. To ensure accurate food consumption records, the nutritionist will provide training on correctly expressing portion sizes using spoons, bowls, ladles, cups, etc., and the patients will be asked to keep a record using a form for 2 weekdays and 1 weekend. In the evaluation of three-day food consumption, the Nutrition Information System (BEBIS) software package containing food compositions specific to Turkey will be used, and the analysis results will be compared with the dietary reference intakes in the recommendations of the Turkish Nutrition Guide.

In the second stage, the intervention group will be determined according to the results of the KIDMED (Mediterranean Diet Quality) scale, which is a pediatric Mediterranean diet adherence scale. The KIDMED scale (Mediterranean Diet Quality) was developed by Serra Majem et al. in 2004. The Turkish validity and reliability study of the scale was conducted by Şahingöz et al. in 2019. The scale consists of 16 questions. The questions are answered with yes (1) and no (2). Items 6, 12, 14, and 16 are scored as -1, and the remaining 12 items are scored as +1. In the evaluation of the scale, ≤ 3 is considered low adherence, 4-7 is considered moderate adherence, and ≥ 8 is considered high adherence. In our study, those in Group B who did not meet metabolic targets, and those with KIDMED results deemed "poor" and "needing improvement," will form the intervention group (Group C).

Adolescents in Group C will be scheduled for a 12-week Mediterranean diet intervention. The Mediterranean Diet training is planned as a 30-45 minute face-to-face meeting, and the brochure to be used in the training is available in Appendix 1. Visits will be made by phone between weeks 2-3 and weeks 7-9, and diet compliance will be monitored with dietitian consultations, with additional motivational consultations provided if necessary. A face-to-face meeting will be held in week 12, and anthropometric measurements will be repeated. Three-day food consumption records will be taken. Biochemical data obtained during routine 3-month follow-up will be retrieved from file information. Oxidative stress markers will be repeated.

If there are cases in Group A that are poor or needing improvement, these individuals will also receive Mediterranean Diet training, and their follow-up will continue with the dietitian of the department they are being monitored by. Participants in group B who received a 'good' KIDMED score will continue with standard medical nutritional therapy under the guidance of a dietitian.

Inclusion Criteria:

• Ages 10-18 years
• BMI between the 5th and 95th percentile (normal to overweight)
• Diagnosis of Type 1 Diabetes for ≥1.5 years
• Users of a continuous glucose monitoring (CGM) system
• No other comorbidities and not taking medications
• Non-smokers and non-alcohol users (including e-cigarettes)
• Written informed consent provided by the participant and their parent/guardian

Exclusion Criteria:

• Presence of any acute or chronic disease other than Type 1 Diabetes
• Current use of any medications
• BMI ≥ 95th percentile (obese)
• Presence of an eating disorder
• Use of tobacco, e-cigarettes, or alcohol