This observational study was planned to determine the relationship between dietary antioxidant intake and thiol disulfide homeostasis of individuals with type 2 diabetes. One of the current approaches in medical nutrition therapy of diabetes is to increase the consumption of foods with high antioxidant content in order to strengthen antioxidant defense. Increased dietary antioxidant intake may have both protective and therapeutic effects by reducing the risk of diabetes and preventing complications that may occur. It is known that dynamic thiol disulfide balance can be a good indicator of antioxidant defense in individuals with diabetes, and there are limited studies on this subject.

Power analysis was performed to determine the study sample. In order to reveal a moderate to high level effect for each parameter with 80% power and 5% margin of error, it was found appropriate to work with a total of 68 people, 34 of whom were T2DM and 34 of whom were healthy. In order to keep the sample size higher, a total of 87 individuals, including 40 T2DM and 47 healthy individuals, were included in this study. Individuals who agreed to participate in the study gave their informed consent. Anthropometic measurements (body weight and height) were taken by the researcher. BMI values of individuals were calculated with the formula of body weight (kg)/height (m)2 Routine fasting plasma glucose (FPG), hemoglobin A1c (HbA1c), total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, very low-density lipoprotein (VLDL), non-HDL cholesterol, Total/HDL cholesterol ratio, triglyceride (TG), C-reactive protein (CRP) values were analyzed with blood samples taken by the nurse on an 8 hours of fasting in the morning. Dynamic thiol disulfide balance was determined by native thiol, total thiol and disulfide values and oxidized albumin was determined by IMA values. Food consumption records of individuals were taken to determine dietary antioxidant intake and dietary antioxidant capacity. Oxidative balance score was used to evaluate the exposure of individuals to antioxidants and prooxidants. Descriptive statistics for categorical variables are presented as frequency and percentage. The conformity of the numerical variables to the normal distribution was checked using the Shapiro-Wilk Test. The descriptive statistics of numerical variables were given as mean (±) standard deviation for those with normal distribution, and median interquartile range [IQR] values for those without normal distribution. In the comparison of two independent groups; Independent Sample T Test was used if the data provided the assumptions of the parametric tests, the Mann-Whitney U Test was used if the assumptions of the parametric tests were not met, and the Chi-square Test was used for the comparison of two qualitative groups. Examination of the relationships between quantitative variables was determined by the "Pearson Correlation Coefficient" for those with normal distribution and the Spearman Correlation Coefficient for those who did not. In the interpretation of the correlation coefficient, very weak correlation criteria were used if <0.2, weak correlation between 0.2-0.4, moderate correlation between 0.4-0.6, high correlation between 0.6-0.8, and very high correlation if 0.8>. Statistical significance level was considered as α<0.05, α<0.01, α<0.001 in all calculations and interpretations and hypotheses were established as bidirectional. Statistical analysis of the data was performed with SPSS v26 (IBM Inc., Chicago, IL, USA) statistical package program.

Inclusion Criteria (for case group):

• Diagnosis with type 2 diabetes mellitus
• Diabetes age for a maximum of 5 years
• Body mass index (BMI)<30 kg/m^2
• Received and applied medical nutrition therapy and metformin therapy

Inclusion Criteria (for control group):

• Body mass index (BMI) <30 kg/m^2

Exclusion Criteria (for case group):

• Receiving insulin therapy
• Developing diabetes-specific complications
• Smoking tobacco
• Consuming alcohol
• Having end-stage chronic renal failure
• Receiving chemotherapy and/or radiotherapy
• Being in menopause, pregnant and/or lactation period
• Using antioxidant vitamin and mineral supplements

Exclusion Criteria (for control group):

• Smoking tobacco
• Using alcohol
• Having any chronic disease
• Having end-stage chronic renal failure
• Receiving chemotherapy and/or radiotherapy
• Being in menopausal, pregnant and/or lactation period,
• Using antioxidant vitamin and mineral supplements
• Following any diet program

Participants who applied to Ankara City Hospital Endochronology Polyclinic between January and April 2021.