Background: Metabolic syndrome (MetS) and chronic kidney disease (CKD) share features such as inflammation and oxidative stress. Fruit- and vegetable-derived polyphenols may modulate these mechanisms. 

Background: To evaluate effects of fruit- and vegetable-based polyphenol interventions on metabolic and renal outcomes in adults with MetS or CKD/ESRD. 

Methods: We systematically reviewed randomized controlled trials comparing polyphenol-rich whole foods or supplements versus control. Data on lipids, blood pressure, glucose, endothelial function, estimated glomerular filtration rate (eGFR), albuminuria, and cardiovascular events were extracted and narratively synthesized. 

Results: Twenty-eight RCTs (n = 20-108) were included. In MetS, bergamot extract (six months) reduced LDL by 22% and triglycerides by 23% (p < 0.01). Grape powder (60 g/day for four weeks) lowered triglycerides and improved HDL function. Freeze-dried blueberry (45 g/day for six weeks) enhanced endothelial function (p < 0.05). Blood pressure reductions occurred with grape polyphenols; glycemic improvements were limited to polyphenol-rich diets and high-dose resveratrol. In CKD, fruit and vegetable diets (up to five years) slowed eGFR decline and increased plasma bicarbonate to levels comparable to sodium bicarbonate. Long-term interventions (five years) reported zero cardiovascular events versus six in controls (p < 0.01). Isolated supplements (e.g., cranberry, resveratrol) showed minimal effects on renal function. No serious adverse events were reported. 

Conclusion: Whole-food polyphenol interventions improve lipid profiles, endothelial function, and slow renal decline in MetS and CKD populations. Glycemic benefits are modest. Standardized, long-term RCTs are needed to refine dietary guidelines.