Dietary intake and diabetic retinopathy: A systematic review

Methodological quality of the review: Medium confidence

Author: Wong MYZ, Man REK, Fenwick EK, Gupta P, Li LJ, van Dam RM, Chong MF, Lamoureux EL

Region: None specified

Sector: Diabetic retinopathy

Sub-sector: Diet, risk

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Narrative synthesis

Qualitative synthesis method: Not applicable

Background:

There are a few comprehensive reviews on diet and DR, with existing reviews mostly either focused on a specific nutrient or food group (e.g. alcohol, micronutrients) or providing only a summary of the potential of the diet to influence DR pathogenic mechanisms. Authors note that at the time of writing, there were no comprehensive reviews of the entire spectrum of dietary components and their association or effects on DR as a clinical outcome. The evidence linking dietary intake with diabetic retinopathy (DR) is growing but unclear.

Objectives:

Determine the association between dietary intake and DR.

Main findings:

Authors included a total of 31 studies (three interventional, 28 Observational) in the review. The majority of the observational studies had high Newcastle Ottawa Scale scores, with 25 classified as high quality and three a moderate quality. Of the three interventional studies, two were attributed high risk and one medium risk of bias. Authors found that higher intakes of dietary fiber, oily fish, and greater adherence to a Mediterranean diet were protective of DR. Conversely, authors note that high total caloric intake was associated with higher risk of DR. No significant associations of carbohydrate, vitamin D, and sodium intake with DR were found. Associations of antioxidants, fatty acids, proteins and alcohol with DR remain equivocal.

Methodology: 

Authors’ inclusion criteria consisted of both interventional and observational studies. Studies had to include participant with Type 1 and Type 2 diabetes. Interventions included exposures had to measure a form of dietary intake, either through standard dietary methods, general interviewer-administered questionnaires or estimations from biomarker levels. Authors note that dietary intake included the consumption of specific foods and beverages, the intake of micro/macronutrients, and adherence to meal patterns. Outcome measures included prevalence, incidence or progression of DR or diabetic macula edema.

Authors conducted a search on PubMed, Embase, Medline and Cochrane Central Register of Controlled Trials, from 1967 to 2017 with no language restrictions. Authors searched the databases using a combination of the following keywords: Diet OR Dietary factors OR Dietary Intake OR intake OR Consumption OR food OR nutrition OR dietary protein OR antioxidant OR Nutrient OR Fibre OR carbohydrate OR fat OR fatty acid OR glycemic food OR vegetables OR Fruit OR vitamin OR caffeine OR fish OR alcohol OR calorie OR caloric OR Mediterranean AND Diabetic Retinopathy OR Diabetic Complications OR Microvascular Complications OR Diabetic Macular Edema.

Two authors independently screened studies for inclusion. To extract data of included studies, authors used ‘Strengthening the Reporting of Observational Studies in Epidemiology’ (STROBE) statement. One author extracted the data and a second one vetted the extraction. Quality assessment of observational studies were assessed using the Newcastle Ottawa Scale and interventional studies were assessed using the Cochrane Collaboration Risk of Bias tool.

Authors conducted a narrative synthesis of included studies in the review.

Applicability/external validity:

Authors note that findings from this study generally support existing American Diabetic Association (ADA) guidelines for overall diabetes management that acknowledge the beneficial effects of a Mediterranean diet, encourage people with diabetes to consume a diet rich in fruits and vegetables, and recommend lower caloric intakes.

Geographic focus:

Authors do not report the geographical location of included studies.

Summary of quality assessment:

Overall, there is medium confidence in study findings as some important limitations were identified. Authors did not conduct a thorough search to ensure that grey literature was included in the review. In addition, it is not clear if two authors extracted data of included studies independently avoiding biases. Authors appropriately conducted a narrative synthesis of included studies due to the heterogeneity nature of included studies.