Table 1.

Dietary and food patterns and DR.

References	Study design	Study period	Endpoint	Subjects (age, sex, number…)	Method	Results	Strength of evidence
Diaz-Lopez et al. (30)	Post-hoc analysis of a randomized trial	6 years (from 2003 to 2009)	To determine the effect of the three dietary interventions on the incidence of diabetes complications.	Type 2 diabetes participating in the “PREvencion con DIeta MEDiterranea (PREDIMED)” randomized clinical trial, who were free of microvascular complications at enrolment (n = 3,614, aged 55–80 years)	Patients were randomly assigned to one of three dietary interventions: MedDiet supplemented with extravirgin olive oil (MedDiet+EVOO), MedDiet supplemented with mixed nuts (MedDiet+Nuts), or a low-fat control diet. Two independent outcomes were considered: new onset of diabetic retinopathy and nephropathy. Hazard ratios (HRs) were calculated using multivariable-adjusted Cox regression.	Compared with the control diet, multivariable-adjusted HRs for diabetic retinopathy were 0.56 (95% CI 0.32–0.97) for the MedDiet+EVOO and 0.63 (0.35–1.11) for the MedDiet+Nuts. No between-group differences were found for nephropathy.	Moderate
Salas-Salvadó et al. (31)	Post-hoc analysis of a randomized trial	8 years (2003 to 2011)	To assess the efficacy of Mediterranean diets for the primary prevention of diabetes in the Prevención con Dieta Mediterránea trial.	7447 partecipants at high cardiovascular risk, aged between 55 and 80 years (57% were female)	Participants were randomly assigned and stratified by site, sex, and age but not diabetes status to receive 1 of 3 diets: Mediterranean diet supplemented with extra-virgin olive oil (EVOO), Mediterranean diet supplemented with nuts, or a control diet (advice on a low-fat diet). No intervention to increase physical activity or lose weight was included.	A Mediterranean diet enriched with EVOO but without energy restrictions reduced diabetes risk among persons with high cardiovascular risk.	Moderate
Sala-Vila et al. (32)	Prospective randomized trial	6 years (From 2003 to 2009)	To determine whether LCω3PUFA intake relates to a decreased incidence of sight-threatening DR in individuals with type 2 diabetes older than 55 years	3,614 individuals aged 55 to 80 years with a previous diagnosis of type 2 diabetes, participating in the “PREvencion con DIeta MEDiterranea (PREDIMED)” randomized clinical trial, considering only subjects with type 2 diabetes at baseline.	Dietary intake was assessed at baseline and yearly during follow-up up by using a 137-item semiquantitative food-frequency questionnaire validated for the PREDIMED study. Information on seafood products was collected in 8 items of the questionnaire (uncanned oily fish; lean fish; smoked/salted fish; mollusks; shrimp, prawn, and crayfish; octopus, baby squid and squid; oily fish canned in oil; and oily fish canned in salted water).	In middle-aged and older individuals with type 2 diabetes, intake of at least 500 mg/d of dietary LCω3PUFA, easily achievable with 2 weekly servings of oily fish (as recommended in the Mediterranean diet), is associated with a decreased risk of sight-threatening DR.	Moderate
El Bilbeisi et al. (33)	Cross sectional study	2 years (from 2015 to 2016)	To identify major dietary patterns among DM2 pt and its association with diabetes complications	1,200 T2DM patients, selected by a cluster random sampling method, aged 20–64 years receiving care in the primary healthcare centers (PHCs) in Gaza Strip, Palestine, (59.8% females, 40.2% males)	Data about dietary patterns were collected by an expert nutritionist, using a validated semi-quantitative food frequency questionnaire (FFQ). Dietary patterns were obtained using factor analysis after the classification of food items into 25 groups.	The Asian-like dietary pattern (high intake of whole grains, potatoes, beans, legumes, vegetables, tomatoes and fruit) is associated with a lower prevalence of diabetes complications among DM2 patients rather than sweet-soft drinks-snacks pattern	Low
Tanaka et al. (34)	Cohort	8 years (from 1995 to 2003)	To establish the effect of fruit & vegetables (Vitamin C, Vitamin E, Carotenoids, fiber) intake on DR incidence	This study is part of the Japan Diabetes Complications Study, an open-labeled randomized trial originally designed evaluate the efficacy of a long-term therapeutic intervention focused on lifestyle education. It included 978 patients aged 40–70 years.	Baseline dietary intake was assessed by a food frequency questionnaire based on food groups and 24-h dietary records. Primary outcome was incident diabetic retinopathy determined using international severity scales.	Adequate fruit consumption of 173.2 g per day was associated with a 50% reduced risk of DR incidence, compared with consumption of 53.2 g of fruit per day or less	Low
Bazzano et al. (35)	Retrospective	4 years (from 1971 to 1975)	To examine the association of fruit and vegetable intake with the risk of cardiovascular disease	9608 adults aged 25–74 years participating in the first National Health and Nutrition Examination Survey Epidemiologic Follow-up Study and free of cardiovascular disease at the time of their baseline examination.	Fruit and vegetable intake at baseline was measured with a food-frequency questionnaire.	The frequency of fruit and vegetable intake is inversely associated with stroke incidence and mortality, ischemic heart disease mortality, cardiovascular disease mortality, and all-cause mortality in the general US population. fruit and vegetables should be consumed in each meal in adequate quantities equal to at least 400 g per day. Each additional serving of fruit and vegetables reduces the risk of cardiovascular events by 4% and stroke by 5%	Low
Sala-Vila et al. (36)	Randomized controlled trial	2 years	To examinate the cognitive effects of a 2-years walnut intervention in cognitively healthy elders	636 participants (63–79 yeras old, 68% women) of the Walnuts And Healthy Aging (WAHA) study (Barcelona, Spain; Loma Linda, CA)	The participants were randomly allocated to a diet enriched with walnuts at ~15% energy (30–60 g/d) or a control diet (abstention from walnuts). a comprehensive neurocognitive test battery was administered at baseline and 2 years.	Walnut supplementation for 2 y had no effect on cognition in healthy elders. However, brain fMRI and post-hoc analyses by site suggest that walnuts might delay cognitive decline in subgroups at higher risk.	Moderate
Nunes et al. (37)	Case-control study	/	To characterize the association of lifestyle and nutritional risk profiles with age-related macular degeneration (AMD) in two subpopulations with differing AMD prevalence.	1,992 participants included 768 patients with AMD and 1,224 age- and sex-matched participants without AMD	Enrolled participants completed a validated lifestyle and food frequency questionnaire. A score to measure adherence to the Mediterranean diet (mediSCORE; Range, 0–9) was constructed from individual food intakes, which were further analyzed by conversion to nutrient consumption	High adherence to a Mediterranean diet and regular physical activity seem to be protective factors for AMD in a Portuguese population. The effect of the diet is likely driven by the increased consumption of vegetables, fruits, and nut.	Low
Ma et al. (38)	Case-control study	1 year (2013)	To determine the association between regular Chinese green tea consumption and the risk of DR in diabetic patients in China.	200 patients: 100 DR patients and 100 age-sex-matched diabetic controls without retinopathy, including 68 men and 132 women aged 35–85 years	DR was defined from retinal photographs and detailed information on Chinese green tea consumption of the participants was collected through a face-to-face interview.	Diabetic patients who had regularly drunk Chinese green tea every week for at least 1 year in their lives had a DR risk reduction of about 50% compared with those who had not.	Low
Hjellvik et al. (39)	Cohort	4 years (from 2004 to 2008)	To study the association between consumption of filtered boiled coffee consumption and incident of type 2 diabetes.	3,62,045 Norwegians (1,71,414 Men and 1,90,631 Women) aged 40–45 years old at the time of health survey administration.	Information on self-reported coffee consumption was available from health surveys conducted from 1985 to 1999 in Norway. Type 2 diabetes incidences were extimated from redeemed prescriptions of oral antidiabetic drugs in the period 1 January 2004 to 1 January 2008 from the Norwegian Prescription Database.	A moderate inverse association was found between consumption of both boiled and other types of coffee at the age of 40–45 years and the risk of being prescribed oral antidiabetic drugs 5–20 years later.	Low
Tuomilehto et al. (40)	Prospective study	mean follow-up of 12 years	To determine the relationship between coffee consumption and the incidence of type 2 DM among Finnish individuals, who have the highest coffee consumption in the world.	6,974 Finnish men and 7,655 women aged 35 m to 64 years without history of stroke, coronary heart disease, or DM at baseline	Information on self-reported coffee consumption was obtained from combined surveys conducted in 1982, 1987, and 1992. Mean follow-up of 12 years. Main Outcome Measures Hazard ratios for the incidence of type 2DM were estimated for different levels of daily coffee consumption	Coffee drinking has a graded inverse association with the risk of type 2 DM. In both sexes combined, the multivariate-adjusted inverse association was significant (P for trend 0.001) and persisted when stratified by younger and older than 50 years; smokers and never smokers; healthy weight, overweight, and obese participants; alcohol drinker and non-drinker; and participants drinking filtered and non-filtered coffee.	Low