Lifestyle modifications such as weight loss, increasing physical activity, and reducing alcohol consumption and salt intake have been consistently shown to decrease blood pressure. Less well understood is whether increased dietary protein intake may also reduce blood pressure and the risk of hypertension. We conducted a meta-analysis of randomized controlled trials to assess the hypothesis that increased dietary protein intake decreases systolic and diastolic blood pressure in adults. MEDLINE, EMBASE, Cochrane Library, Web of Science, a registry of soy research trials, bibliography review, and expert consultation were the sources of English and non-English articles published before April 2011. Search terms included randomized controlled trial, blood pressure, dietary proteins, dietary supplements, casein, soy, and meat. Forty randomized controlled trials including 3,277 participants in which amount or source of protein was the only difference between the intervention and comparison groups and that examined blood pressure were included. Using a standardized protocol and data extraction form, two investigators independently abstracted data on study design, participant characteristics, intervention, and treatment outcomes. Net effects of protein on blood pressure were pooled across trials and weighted by the inverse of the variance using random-effects models. Compared to carbohydrate, dietary protein was associated with significant decreases in mean systolic and diastolic blood pressure (95% confidence intervals) of -1.75 (-2.31, -1.19) and -1.16 (-1.60, -0.72) mmHg, respectively (all P<0.001). Blood pressure lowering effects of both vegetable and animal sources of protein were observed with significant decreases of -2.22 (-3.18, -1.26) and -2.54 (-3.55, -1.53) mmHg for systolic blood pressure, respectively (all P<0.001), and -1.25 (-2.12, -0.39) and -0.95 (-1.72, -0.19) mmHg for diastolic blood pressure, respectively (P=0.005 and 0.01, respectively). Blood pressure reduction was not significantly different when vegetable protein was compared directly to animal protein. In conclusion, dietary protein intake reduces systolic and diastolic blood pressure in adults. Replacement of carbohydrate intake with protein intake, from either vegetable or animal sources, could be an important strategy for helping to curb the growing pandemic of hypertension and related cardiovascular disease morbidity and mortality. Future research is indicated to assess potential differential effects of protein on blood pressure according to hypertension status.
Epidemiological Evidence of the Association between Dietary Protein Intake and Blood Pressure: A Meta-Analysis of Published Data.