July 16, 2010 -- A Mediterranean-style diet -- one that is rich in fresh fruits, vegetables, and whole grains and low in saturated fats -- promotes heart function even in men who are genetically predisposed to poor heart health.
That is the finding of a new study of twins published in the July issue of Circulation: Cardiovascular Quality and Outcomes, a journal of the American Heart Association.
“This means that the autonomic system controlling someone’s heart rate works better in people who eat a diet similar to a Mediterranean diet,” study leader Jun Dai, MD, PhD, said in a written statement. Dai is an assistant professor of nutrition and epidemiology in the Applied Health Science Department at Indiana University in Bloomington.
A Mediterranean-style diet refers to the traditional cooking style of countries bordering the Mediterranean Sea. The diet includes: fish, legumes, fruits, vegetables, whole grains, and nuts; spices and herbs to flavor foods rather than salt; and wine in moderation. The diet is known to reduce the risk of coronary disease, but until now the mechanism had been poorly understood, Dai and colleagues say.
In this study, however, researchers showed that a Mediterranean-style diet is related to higher heart rate variability (HRV), a measure of the time interval between a person’s heart beats during everyday life.
Lower heart rate variability is a risk factor for coronary artery disease. Higher heart rate variability reflects good autonomic function of the heart and shows that the organ has a higher capacity to adjust to the challenges and variations that come its way, Dai tells WebMD. Such challenges include responding to temperature changes and breaking down nutrients after eating, she says.
In order to conduct their analysis, the researchers administered food frequency questionnaires to 276 middle-aged male twins. Diet can influence heart rate variability, but this association can be confounded by environmental and genetic factors. Using twins enabled researchers to examine the influence of diet on heart rate variability while controlling for genetic and other familial influences.
Using a published algorithm, researchers approximated how closely the men’s diets conformed to a Mediterranean-style diet and then scored each participant; the higher the score, the greater the similarity to the Mediterranean-style diet.
To measure heart rate variation, all twins had their heart’s electrical activity continuously measured and recorded with a Holter monitor, a portable, battery-operated electrocardiogram device.
Findings showed that the more a person’s diet resembled a Mediterranean-style diet, the more variable the heart beat-to-beat time interval -- 10% to 58% (depending on the HRV measure considered) for men in the top Mediterranean diet score quarter compared to those in the lowest quarter; this equates to a 9% to 14 % reduction in heart-related death.
Genetic influence on heart rate variability frequency ranged from 20% to 95%, depending on the heart rate variability measure considered.