NEW YORK (Reuters) -- Most people know that it's best to avoid a high-fat diet and it's good to aim for one rich in fruits, vegetables, and grains. But, what about protein?
According to an international study of more than 10,000 men and women, a protein-rich diet may lead to lower blood pressure. More study is needed to determine whether the blood pressure drop is due to a diet rich in animal or vegetable protein, or if it's due to some other factor associated with such intake, according to the report in the October 1 issue of the American Heart Association's journal, Circulation.
"Further work is needed to clarify and verify the independence and reproducibility of the relation," wrote lead study author, Dr. Jeremiah Stamler, of the Department of Preventive Medicine at the Northwestern University Medical School in Chicago.
"Also, research is needed on the association of individual dietary amino acids -- singly and in combination -- with blood pressure," wrote the study authors. Amino acids are the building blocks for proteins.
In the International Study of Salt and Blood Pressure, or INTERSALT, Stamler and colleagues looked at 10,020 men and women, aged 20 to 59, from 32 different countries. They measured the study participants' blood pressure, and tested their urine for three substances associated with protein intake -- total nitrogen, urea, and sulfate, which is an indicator of sulfur-containing amino acids.
After taking into consideration age, sex, alcohol intake, body mass, and other variables, they found that those with 30% higher than average protein intake had blood pressure 2 to 3 points lower in both systolic and diastolic figures (upper and lower numbers in a blood pressure reading), than those who ate 30% less protein on average.
"This report deals with data on a long-standing unsolved problem: the relationship of dietary protein to blood pressure," said Stamler.
However, because no dietary data was collected, it is unclear what the source of protein was -- whether animal or vegetable. And the results may be complicated by an increased calorie or fat intake along with the protein, or there may be a specific factor in the protein associated with blood pressure change.
Protein can be found in foods such as meat, fish, dried beans, and dairy products. The current dietary guidelines recommend that 10% to 15% of calories be obtained from protein.
In the study, those in the low-protein group consumed 44 grams per day, and those in the high protein group ate 81 grams of protein per day. A small chicken breast, glass of skim milk, and a cup of low-fat yogurt is the equivalent of 50 grams of protein.
SOURCE: Circulation (1996;94:1629-1634)
