Diabetic macular edema can develop at all stages of diabetic retinopathy, causing visual impairment and blindness. Modern diets are high in advanced glycation end products (dAGEs), derived from processing methods, exerting a pivotal role in promoting diabetic retinopathy risk. In this cross-sectional study, we investigate the relationship between dietary and serum levels of AGEs and DME in type 2 diabetic subjects.

This was a cross-sectional study was carried out in the Hacettepe University Hospital, Department of Ophthalmology, between July 2018 and February 2019.

While benefiting from the results of the previous studies, the sample size of the research was type 1 error level α = 0.05 and type 2 level β = 0.20. The power analysis was statistically calculated using NCCS PAS 11 program. The present study was conducted with 90 patients: 50 case-patients (DM with DME) and 40 control patients (DM without DME). Excluded from the study were those under the age of 18 years, with no diagnosis of Type 2 DM, without any anti-diabetic agent, with any disease other than DME and DR that may affect the retina, with any disease that may affect the retina for the control group, with corneal, lens or vitreous opacification preventing Optical coherence tomography (OCT) withdrawal, with any systemic disease other than DM and hypertension, with a history of eye surgery, and with blindness or infection in the eye, along with those recently diagnosed with diabetes (<1 year) and those with special diets.

This the study was conducted in accordance with the Declaration of Helsinki Ethical Principles.

OCT withdrawals and CFT evaluations of those included in the study were made by the doctor and directed to the dietician (researcher). Demographic data and the dietary habits were collected through standardized face-to-face interviewer-assisted questionnaires. The bodyweight and height of patients were measured using a calibrated body composition analyser and weight scales by researcher. BMI was evaluated based on the WHO classification. Waist and hip circumference was also measured and evaluated in terms of high risk of developing chronic diseases. Hypothesis: If the waist/hip ratio is ≥0.85 for women and ≥0.90 for men, the risk of developing chronic diseases increases.

Diabetic macular edema (DME) Examination After a detailed systemic and ophthalmological history was taken from all subjects by the doctor, the best-corrected visual acuity level was measured using an ETDRS chart. A fundus examination was performed with a 90 D lens after anterior segment examination and pupil dilation with a biomicroscope. A spectral-domain OCT (Spectralis OCT, Heidelberg Engineering, Heidelberg, Germany) was applied for the evaluation of CFT. After a minimum of eight hours of fasting, approximately 5 ml of peripheral venous blood was collected from the antecubital region in the HÜTF Ophthalmology Clinic between 08:00 and 10:00.

Assessment of dietary intake and dietary AGEs The dietary intake of participants was assessed using a validated quantitative food frequency questionnaire (QFFQ) (including about 110 food items take 20-25 minutes to complete). Foods were classified into eight categories: dairy products, meat products, fruits, vegetables, bread and cereals, beverages, and desserts. Also, questions were asked to patients about traditional cooking methods to calculate dietary AGE intakes. Such as what cooking methods do they cook the foods? How long do they cook the food? Standardized food recipes for Turkey and the Nutrition Information System (BEBIS) program were used to calculate the average daily energy and nutrient intake for each participant. Meanwhile, to assess dietary AGEs from the QFFQ, each food's contribution to dAGEs intake was calculated based on the Advance Glycation End Products in Foods Table published by the Uribarri et al., which comprises data on 549 food items.

Sample Collection and Analysis The serum samples collected during the research were delivered to the laboratory while preserving the cold chain. The enzyme-labeled immune "Enzyme-Linked Immunosorbent Assay (ELISA)" test was performed with biologists of the company using a Biotek 800TS device. While analyzing the samples, Human CML Elisa Kit 96 tests for serum AGE and Human RAGE Elisa Kit 96 test kits for serum RAGE were used. Carboxymethyl lysine (CML) was considered as the AGE parameter, being the most easily detected and the most abundant type of AGE in humans. The minimum detectable dose of CML in humans is typically less than 15.6 pg/ml.

Inclusion Criteria:

• Included from the study were those over the age of 18 years, with diagnosis of Type 2 DM.

Exclusion Criteria:

• Excluded from the study were those under the age of 18 years, with no diagnosis of Type 2 DM, without any anti-diabetic agent, with any disease other than DME and DR that may affect the retina, with any disease that may affect the retina for the control group, with corneal, lens or vitreous opacification preventing Optical coherence tomography (OCT) withdrawal, with any systemic disease other than DM and hypertension, with a history of eye surgery, and with blindness or infection in the eye, along with those recently diagnosed with diabetes (<1 year) and those with special diets.