In this prospective cohort study, higher DDRRS was inversely associated with CKD, independent of age, sex, smoking, total energy intake, BMI, hypertension, diabetes, eGFR, and physical activity, after 5.98 years of follow-up.
Although no study has yet investigated the association between DDRRS and CKD, dietary patterns withsimilar beneficial components as DDRRS have shown an inverse relation with CKD[23, 24]. One of such patterns is Dietary Approaches to Stop Hypertension (DASH) style diet, includinghigh intake of whole grains, nuts and legumes and low intake of red and processed meat and sweetened beverages, similar to DDRRS. Previously, it has been reportedthat DASH dietcanreduce CKD risk by 59%. Mediterranean dietary pattern is another example,including high intake of fruits and nuts, vegetables, cereals, legumes, fish, monounsaturated to saturated fatty acid ratio, and low intake of meat and dairy products;this dietary pattern was associated with 47% decrease in CKD incidence . Furthermore, subjects in the lower quartile of DDRRS in our study presented a more western like dietary pattern, which adversely affected the risk of CKD by being abundant in refined grains, sugary drinks, saturated and trans fat, but poor in whole grains and PUFA, according to previous studies .
Several components of DDRRS have been individually associatedwith kidney function [9–12, 14, 26, 27]. Gopinath et al. reported that a high GI intake increased the likelihood of having eGFR < 60 mL/min/1.73 m2 by 55%, while the highest dietary cereal fiber intake was associated with a 50% lower CKD risk . Consumption of sugar sweetened beverages was another component of DDRRS, which has been proved to increase risk of CKD [14, 26]. Findings of the current study demonstrated that higher adherence to DDRRS was accompanied by higher total carbohydrate and fiber but lower sugar consumption. According to a recent study, low-carbohydrate, high-protein diet can lead to higher CKD risk . The detrimental effect of such a diet on kidney has been partly explained by the lower intake of dietary fiber. Studies have shown that dietary fiber intake can reduce the risk of CKD and enhance kidney function [13, 29–31].
The beneficial effect of DDRRS could be partly attributed to the inclusion of nuts as positive, and red and processed meat as negative components. Our findings also indicate that animal protein consumption declined and plant protein consumption increased along with higher adherence to DDRRS. Red and processed meat intake has been directly associated with risk of hypertension  and CKD . However, intake of nuts had a protective impact on CKD risk . These associations could be explained through various mechanisms, one of which is the difference in metabolism of protein sources. Cooked meat contains a high amount of Maillard Reaction Products (MRPs). MRPs increase oxidative stress and inflammation through various chemical reactions, which in turn can lead to the development of hypertension and kidney dysfunction. Plant sources of protein such as nuts, legumes and whole grain result in to less dietary acid load compared with animal proteins like red and processed meat .
The protective role of PUFA to SFA ratio in DDRRS has been backed up by our previous study, showing a 27% increase in CKD risk for participants in the highest versus lowest quartile of PUFA . Furthermore, another study on the role of fatty acids on kidney dysfunction reported a direct association between saturated fatty acids and albuminuria and CKD . However, they found no significant association with TFA .
Coffee consumption is another component of DDRRS, considered to be beneficial. A recent study on coffee consumption and incident kidney disease demonstrated that each additional cup of coffee per day is associated with 3% decrease in CKD risk . This may be due to antioxidants which protect the glomerular endothelium from oxidative stress and systemic inflammation, or caffeine itself, by increasing eGFR and renal blood flow.
Diet of participants in higher quartiles of DDRRS was richer in potassium, magnesium, and vitamin C, micronutrients previously shown to prevent CKD incident . These protective effects may be due to vitamin C acting as an antioxidant , and magnesium and potassium lower the renal acid load . High magnesium intake may reflect high plant protein consumption, which in turn lowers the amount of fibroblast growth factor 23 and increases bicarbonate levels; thus, protecting against CKD . Furthermore, low serum magnesium concentrations have been suggested to promote endothelial dysfunction by stimulating inflammatory and pro-atherogenic cytokines which can lead to kidney dysfunction . So, these might also explain why higher adherence to DDRRS was associated with a lower risk of CKD in our study.
To the best of our knowledge, this study was the first to investigate the relation between dietary diabetes risk reduction score and incident CKD. A noteworthy strength of our study was its prospective design in a large sized, population based cohort. Additionally, using a valid and reliable FFQ and physical activity questionnaire, we were able to capture habitual dietary intake. We recognize the inherent limitations of our research too, first of which was creatinine measurements which were not repeated within three months to confirm a chronic reduction in eGFR. Secondly, there were missing data on the proteinuria of participants, so we could not consider it in the CKD definition. There was also the risk of some unknown or unmeasured confounders which we might have failed to take into account.