The authors conducted a meta-analysis of randomized controlled trials to evaluate the association of dietary protein intake with blood pressure. To identify articles published before April 2011, the authors searched electronic databases, conducted a manual bibliography review, and consulted experts in the field. Forty trials (including 3,277 participants in total) met the eligibility criteria and were included. Using a standardized form, 2 investigators independently abstracted data on study design, participant characteristics, and treatment outcomes. Net change estimates were pooled across trials using random-effects models. Compared with carbohydrate, dietary protein intake was associated with significant changes in mean systolic and diastolic blood pressure of -1.76 mm Hg (95% confidence interval (CI): -2.33, -1.20) and -1.15 mm Hg (95% CI: -1.59, -0.71), respectively (both P 's < 0.001). Both vegetable protein and animal protein were associated with significant blood pressure changes of -2.27 mm Hg (95% CI: -3.36, -1.18) and -2.54 mm Hg (95% CI: -3.55, -1.53), respectively, for systolic blood pressure (both P 's < 0.001) and -1.26 mm Hg (95% CI: -2.26, -0.26) and -0.95 mm Hg (95% CI: -1.72, -0.19), respectively, for diastolic blood pressure (both P 's = 0.014). Blood pressure reduction was not significantly different when vegetable protein was compared directly with animal protein. These findings indicate that partially replacing dietary carbohydrate with protein may be important for the prevention and treatment of hypertension.