Milk and soy protein supplements were associated with a 2.3 and 2.0 mmHg reduction in systolic blood pressure, compared with a refined carbohydrate supplement, according to findings of a randomized clinical trial published in Circulation.
"The systolic blood pressure differences we found are small for the individual, but they are important at the population level," said study leader Jiang He, MD, PhD, from Tulane University.
According to previous research, the New Orleans-based scientists note that a 2 mmHg decrease in systolic blood pressure could lead to 6 percent fewer stroke-related deaths, a 4 percent lower rate of heart disease deaths and a 3 percent reduction in overall deaths among Americans.
According to Dr He, the study's findings suggest that partly replacing refined carbohydrates with foods or drinks high in soy or milk protein may help prevent and treat high blood pressure.
High blood pressure (hypertension), defined as having a systolic and diastolic blood pressure (BP) greater than 140 and 90 mmHg, is a major risk factor for cardiovascular disease (CVD) - a disease that causes almost 50 per cent of deaths in Europe, and reported to cost the EU economy an estimated $200 bn per year.
The researchers recruited 352 people aged 22 or over with pre-hypertension and stage-1 high blood pressure and randomly assigned them to receive either 40 grams per day of protein from soy or milk, or carbohydrate supplementation each for eight weeks. After each intervention, the participants went through a three-week wash out period before crossing over to a different group.
Results showed that soy and milk protein supplementations were associated with reductions in systolic blood pressure of 2.0 and 2.3 mmHg, respectively, but no changes in diastolic blood pressure, compared with the carbohydrate group. Systolic function related to the contraction of the heart, whereas diastolic relates to the filling of the heart with blood.
"Some previous observational research on eating carbohydrates inconsistently suggested that a high carbohydrate diet might help reduce blood pressure," said He.
"In contrast, our clinical trial directly compares soy protein with milk protein on blood pressure, and shows they both lower blood pressure better than carbohydrates."
The researchers concluded: “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.”
Published online ahead of print, doi: 10.1161/CIRCULATIONAHA.110.009159
“Effect of Dietary Protein Supplementation on Blood Pressure: A Randomized, Controlled Trial”
Authors: J. He, M.R. Wofford, K. Reynolds, J. Chen, C-S. Chen, L. Myers, D.L. Minor, P.J. Elmer, D.W. Jones, P.K. Whelton