By Amanda MacMillan
Eating more whole grains—and fewer white, refined ones—can lower diastolic blood pressure and reduce the risk of death from heart disease by almost one-third, says a study published today in the Journal of Nutrition.
Unlike observational trials that have examined the association between whole grains and heart health—but could not prove a cause-and-effect relationship—this study’s controlled, crossover design leaves little room for doubt.
“We went to a fair amount of length and detail to try to eliminate as many things as we could that have, in the past, interfered with our ability to draw conclusions,” says lead author John Kirwan, Ph.D., director of the Metabolic Translational Research Center at the Cleveland Clinic’s Endocrinology & Metabolism Institute. “In the end, it’s as close as you can get to a definitive answer to the question of what whole grains can do for your heart.”
Each of the study’s 33 participants followed two different diets: During one eight-week period, they were given foods with high whole-grain content, and during another eight-week period they got foods made with primarily white flour and refined grains.
Besides the difference in grains, both meal plans were exactly the same—so much so that most of the volunteers didn’t know when they were on which diet. The entrees were prepared by the researchers and provided in plain packages that didn’t reveal whole-grain content.
All of the participants were under age 50 and overweight. At the beginning and end of each eight-week period, researchers recorded their weight, body fat percentage, blood pressure, cholesterol, and other measures of metabolic and cardiovascular health.
Both diets, it turned out, helped the volunteers lose weight and see improvement in several of these areas. They were, after all, eating only the foods and beverages given to them, rather than being allowed to consume freely and normally.
But the researchers suspected that the whole-grain diet would provide additional heart-healthy benefits—and they were right. After the whole-grain diet, participants’ diastolic blood pressure was three times lower than it was following the refined-grain one. Diastolic blood pressure, or the bottom number in a reading, indicates the pressure in the arteries when the heart rests between beats.
Referring to previous research on diastolic blood pressure, the authors concluded that such a drop can reduce the risk of death from heart disease by almost one-third, and the risk of death from stroke by two-fifths.
This impact was even larger than Kirwan had expected. “It was quite remarkable, and a very important message—especially for this age group,” he says. (For adults under 50, the most significant predictor for cardiovascular disease is elevated diastolic blood pressure. For those over 50, systolic pressure becomes more important.)