Background: We quantified the impact of lifestyle and dietary modifications on chronic kidney disease (CKD) by estimating population-attributable fractions (PAFs). Study Design: Observational cohort study. Setting & Participants: Middle-aged adults with type 2 diabetes but without severe albuminuria from the Ongoing Telmisartan Alone and in Combination With Ramipril Global Endpoint Trial (ONTARGET; n = 6,916). Factors: Modifiable lifestyle/dietary risk factors, such as physical activity, size of social network, alcohol intake, tobacco use, diet, and intake of various food items. Outcomes: The primary outcome was CKD, ascertained as moderate to severe albuminuria or >= 5% annual decline in estimated glomerular filtration rate (eGFR) after 5.5 years. The competing risk for death was considered. PAF was defined as the proportional reduction in CKD or mortality (within 5.5 years) that would occur if exposure to a risk factor was changed to an optimal level. Results: At baseline, median urinary albumin-creatinine ratio and eGFR were 6.6 (IQR, 2.9-25.0) mg/mmol and 71.5 (IQR, 58.1-85.9) mL/min/1.73 m(2), respectively. After 5.5 years, 704 (32.5%) participants developed albuminuria, 1,194 (55.2%) had a >= 5% annualeGFRdecline, 267 (12.3%) had both, and 1,022 (14.8%) had died. Being physically active every day has PAFs of 5.1%(95% CI, 0.5%-9.6%) for CKD and 12.3%(95% CI, 4.9%-19.1%) for death. Among food items, increasing vegetable intake would have the largest impact on population health. Considering diet, weight, physical activity, tobacco use, and size of social network, exposure to less than optimum levels gives PAFs of 13.3% (95% CI, 5.5%-20.9%) for CKD and 37.5% (95% CI, 27.8%-46.7%) for death. For the 17.8 million middle-aged Americans with diabetes, improving 1 of these lifestyle behaviors to the optimal range could reduce the incidence or progression of CKD after 5.5 years by 274,000 and the number of deaths within 5.5 years by 405,000. Limitations: Ascertainment of changes in kidney measures does not precisely match the definitions for incidence or progression of CKD. Conclusions: Healthy lifestyle and diet are associated with less CKD and mortality and may have a substantial impact on population kidney health. Am J Kidney Dis. 68(1): 29-40. (C) 2016 The Authors. Published by Elsevier Inc.on behalf of the National Kidney Foundation, Inc. This is an open access article under the CC BY-NC-ND license.