Background: Observational studies have reported an inverse association between dietary protein intake and blood pressure (BP). We compared the effect of soy protein, milk protein, and carbohydrate supplementation on BP among healthy adults.
Methods and results: We conducted a randomized, double-blind crossover trial with 3 intervention phases among 352 adults with prehypertension or stage 1 hypertension in New Orleans, LA, and Jackson, MS, from September 2003 to April 2008. The trial participants were assigned to take 40 g/d soy protein, milk protein, or carbohydrate supplementation each for 8 weeks in a random order. A 3-week washout period was implemented between the interventions. Three BPs were measured at 2 baseline and 2 termination visits during each of 3 intervention phases with a random-zero sphygmomanometer. Compared with carbohydrate controls, soy protein and milk protein supplementations were significantly associated with -2.0 mm Hg (95% confidence interval -3.2 to -0.7 mm Hg, P=0.002) and -2.3 mm Hg (-3.7 to -1.0 mm Hg, P=0.0007) net changes in systolic BP, respectively. Diastolic BP was also reduced, but this change did not reach statistical significance. There was no significant difference in the BP reductions achieved between soy or milk protein supplementation.
Conclusions: The results from this randomized, controlled trial indicate that both soy and milk protein intake reduce systolic BP compared with a high-glycemic-index refined carbohydrate among patients with prehypertension and stage 1 hypertension. Furthermore, these findings suggest that partially replacing carbohydrate with soy or milk protein might be an important component of nutrition intervention strategies for the prevention and treatment of hypertension.
Clinical trial registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00107744.