Table 3.

Fiber, hydratation, 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)	Randomized controlled trial	4 years	To test the effects of two Mediterranean diet (MedDiet) interventions vs. a low-fat diet on incidence of diabetes.	418 non-diabetic subjects aged 55–80 years recruited in one center of the Prevención con Dieta Mediterránea [PREDIMED] study, a large nutrition intervention trial for primary cardiovascular prevention in individuals at high cardiovascular risk.	Participants were randomly assigned to education on a low-fat diet (control group) or to one of two MedDiets, supplemented with either free virgin olive oil (1 liter/week) or nuts (30 g/day). Diets were ad libitum, and no advice on physical activity was given. The main outcome was diabetes incidence diagnosed by the 2009 American Diabetes Association criteria.	The Mediterranean diet, in fact, rich in food sources of fiber, such as fruit, vegetables and unrefined carbohydrates, has been associated with a reduced incidence of DR.	High
Zhang et al. (60)	Cross-sectional study	3 years	To explore the association between hydration status and DR.	5,220 US adults 40 years of age and older (2005–2008 NHANES study)	Serum osmolality was used to assess hydration status for all participants and calculated osmolality was evaluated for only older people.	Adults with lower hydration status had higher risk of DR, moderate/severe non-proliferative retinopathy, and proliferative diabetic retinopathy. Dehydration in older adults, classified by calculated osmolality, is associated with a higher rate of DR.	Low