Background: Diet can affect kidney health through its effects on inflammation. Objective: We tested whether the Adapted Dietary Inflammatory Index (ADII) is associated with kidney function and whether effects of diet on chronic low-grade inflammation explain this association. Methods: This was an observational analysis in 1942 elderly community-dwelling participants aged 70-71 y from 2 independent cohorts: the Uppsala Longitudinal Study of Adult Men (n = 1097 men) and the Prospective Investigation of Vasculature in Uppsala Seniors (n = 845 men and women). The ADII was calculated from 7-d food records, combining putatively proinflammatory and anti-inflammatory effects of nutrients, vitamins, and trace elements. The ADII was validated against serum C-reactive protein (CRP) concentrations. The estimated glomerular filtration rate (eGFR) was assessed from serum cystatin C (cys) and creatinine (crea). Associations between the ADII and eGFR were investigated, and CRP was considered to be a mediator. Results: In adjusted analysis, a 1-SD higher ADII was associated with higher CRP (beta: 6%, 95% Cl: 1%, 10%; P= 0.01) and lower eGFR [Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)(cys): -2.1%, 95% Cl: -3.2%, -1.1%; CKD-EPi(cys+crea): -1.8%; 95% Cl: -2.7%, -0.9%; both P < 0.001]. CRP was also inversely associated with eGFR. Mediation analyses showed that of the total effect of the ADII on kidney function, 15% and 17% (for CKD-EPIcys+crea and CKD-EPIcys equations, respectively) were explained/mediated by serum CRP. Findings were similar when each cohort was analyzed separately. Conclusions: A proinflammatory diet was associated with systemic inflammation as well as with reduced kidney function in a combined analysis of 2 community-based cohorts of elderly individuals. Our results also suggest systemic inflammation to be one potential pathway through which this dietary pattern is linked to kidney function.