Dutch researchers found that when they gave participants either a protein supplement or a supplement with the sweet carbohydrate maltodextrin, people on the protein drink lost an average of 5 points from their systolic blood pressure (the top number in a blood pressure reading), compared with people on the carb-heavy supplement.

It's too soon to make any diet recommendations based on the results, said lead researcher Karianna Teunissen-Beekman, of Maastricht University in the Netherlands.

For one, she noted in an email, it's not clear whether protein, itself, lowers blood pressure. The benefit in this study could have been due to protein users' lower carb intake.

"We first want to get more insight into the biological mechanisms by which proteins lower blood pressure, or carbohydrates increase blood pressure, and the role of different protein and carbohydrate sources," Teunissen-Beekman said.

The study, which appears in the American Journal of Clinical Nutrition, included 99 overweight adults with moderately elevated blood pressure. No one had more than "grade 1" high blood pressure (a systolic pressure of 130 to 159 mm Hg, or a diastolic pressure of 85 to 99 mm Hg).

For the first two weeks of the study, all participants had a sugary drink with each meal every day.

Then for the next four weeks, the men and women replaced their sugary drinks with a supplement they added to water. Individuals were randomly assigned to use either the protein supplement -- a mix of vegetable and dairy proteins -- or the carb-rich one.

After four weeks, the protein group had shaved about 6 points from their systolic blood pressure, versus their own first two weeks on the sugary drink. In contrast, systolic pressure stayed almost unchanged in the carb-supplement group.

That was based on readings taken in the clinic. The researchers also used portable monitors to track people's blood pressure throughout the day.

Those results offered a somewhat different picture. People who used the protein supplement tended to have lower systolic pressure at certain points of the day compared to their initial two weeks on the sweetened drink.

But in the carb-supplement group, systolic pressure tended to be higher at various points throughout the day than it had been during the study's first two weeks.

"From these findings it is not clear whether it is the increased protein or the reduced carbohydrate intake that is responsible for the difference between the two groups," Teunissen-Beekman said.

She said that research into exactly how protein and carbs affect blood pressure regulation should help clear up that question.

Regardless, she noted, managing high blood pressure will never be a matter of changing one item in a person's diet. Overall lifestyle -- including shedding pounds if they are overweight -- is key, and many people need to take medication.

"Managing blood pressure in overweight individuals in real life has more angles than just prescribing supplements," Teunissen-Beekman said.

But, she added, studies have already shown that replacing some carbs with protein can help people with weight control. If future studies show there are blood pressure benefits too, she said, that would give extra support to the diet tactic.

The study was funded by TI Food and Nutrition, which is described as a "public private partnership of science, industry and government" that conducts nutrition research. Its partners included food and supplement manufacturers. SOURCE: American Journal of Clinical Nutrition, online February 22, 2012.

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