The findings, published today in the Journal of Nutrition, suggest that whole grains can be a key regulator of blood pressure, and could provide an effective nutritional strategy to reduce cardiovascular-related deaths and disorders.
“Heart disease and strokes are a leading cause of death in the United States,” Dr. Kirwan says. “This research shows that eating whole grains reduces the risk factors for heart disease.”
Dr. Kirwan is director of the Metabolic Translational Research Center, which is part of Cleveland Clinic’s Endocrinology & Metabolism Institute.
In the study, a group of 33 overweight and obese adults followed either a whole-grain diet or a refined grain diet for two eight-week periods.
The diets were exactly the same, except for whether they consisted of whole grains or refined grains.
At the beginning and end of each diet period, the participants underwent three days of metabolic testing in a clinical research setting.
Those on the whole-grain diet saw a three-fold greater improvement in their diastolic blood pressure compared to when they ate the refined-grain diet.
Blood pressure typically is recorded as two numbers. The systolic is the top number, which measures the pressure in the arteries when the heart beats. Diastolic is the bottom number, which measures the pressure in the arteries when the heart muscle is resting between heartbeats.
Before age 50, an elevated diastolic blood pressure is associated with increased cardiovascular disease risk.
Based on large populations studies, the improvement seen after the whole grain diet equates to reducing the risk of death from heart disease by almost a third, and the risk of death from a stroke by two-fifths, Dr. Kirwan says.
“The result that was most intriguing was the greater improvement in diastolic blood pressure after the whole-grain diet; diastolic blood pressure is the pressure associated with the relaxation of the heart and blood vessels,” Dr. Kirwan says. The number was reduced by a substantial amount.”
Hypertension – or high blood pressure – is a common obesity-related condition that affects about 30 percent of U.S. adults and is a major risk factor for cardiovascular disease.
As people with elevated diastolic blood pressure get older, they are at a higher-than-average risk of developing elevated systolic blood pressure.
All participants saw substantial reductions in body weight, fat loss, systolic blood pressure, total cholesterol, and LDL cholesterol during both diet periods. However, the researchers say, these differences were due to the participants changing their usual eating habits to the carefully controlled diets.
“Both were healthy diets, and both diets had similar amount of calories and were from healthy foods. The only difference was the whole grain,” Dr. Kirwan says.
More research is needed to figure out what it is about whole grains that caused the drop in diastolic blood pressure, Dr. Kirwan says.
In the meantime, the study shows that it’s a smart move to add whole grains to your diet and drop the refined grains, he says.
The recommendations from the United States Department of Agriculture is for Americans to eat 50 grams of whole grain a day, he says. Currently, U.S. adults are eating about 16 grams a day on average.
“So we have a lot of room for improvement — and that improvement could improve your cardiovascular profile, and reduce your risk for disease,” Dr. Kirwan says.