Effects of dietary polyphenols in the glycemic, renal, inflammatory, and oxidative stress biomarkers in diabetic nephropathy: a systematic review with meta-analysis of randomized controlled trials

Abstract

Abstract Context Polyphenols have antioxidant, anti-inflammatory, and anti-glycation properties. Objective To assess the effects of dietary polyphenols, from food sources or supplements, on the anthropometric, glycemic, renal, inflammatory, and oxidative stress markers in adults with diabetic nephropathy (DN). Data sources Systematic searches for randomized clinical trials were performed in MEDLINE, Embase, CENTRAL, Web of Science, LILACS, SciELO, opengrey.eu, and ClinicalTrials.gov databases until December 2021. Data extraction Studies with adults with DN were included. Random-effects meta-analyses were conducted. Risk of bias of the studies and Grading of Recommendations, Assessment, Development, and Evaluation assessment were carried out. Data analysis The searches resulted in 5614 unique occurrences, and 34 full-text articles were retrieved. Of these, 17 studies were included in the qualitative synthesis. Most of the studies used soy protein or milk (n = 5; 0.5–1 g/kg of body weight/d of soy protein, or introduction of 240 mL/d of soy milk) or turmeric/curcumin (n = 5; dose range, 80 to 1500 mg/d) as the intervention. The following outcomes were analyzed: body mass index, glycated hemoglobin (HbA1c), proteinuria, creatinine clearance, glomerular filtration rate (GFR), urinary albumin to creatinine ratio, and levels of fasting blood glucose, insulin, serum urea and creatinine, C-reactive protein, serum tumor necrosis factor-α, and serum malondialdehyde (MDA). The polyphenol intervention significantly decreased HbA1c (n = 7 studies; –0.27% [95%CI, –0.51%, –0.04%]), proteinuria (n = 5 studies; –109.10 [95%CI, –216.57, –1.63] mg/24 h), and MDA (n = 5 studies; z-score: –0.41; 95%CI, –0.71, –0.10), and significantly increased GFR (n = 7 studies; 3.65 [95%CI, 0.15–7.15] mL/min/1.73 m2). Overall, studies showed a high risk of bias, and outcomes showed a low or very-low quality in the Grading of Recommendations, Assessment, Development, and Evaluation assessment. Conclusions There is a clinically modest effect of dietary polyphenols intervention in HbA1c, proteinuria, GFR, MDA, and C-reactive protein levels in patients with DN. It is impossible to establish clinical recommendations, because the evidence was of’ low or very-low quality and because of the heterogeneity of types and dose regimens used in the studies. Systematic Review Registration PROSPERO registration no. ID245406.