The types of food eaten in an effort to cut down on saturated fat may make a difference in reducing heart disease risk, according to a study of people with either high blood pressure or prehypertension. The study was supported by the National Heart, Lung, and Blood Institute (NHLBI), a part of the National Institutes of Health.
Investigators evaluated three diets that follow the principles of NHLBI’s DASH (Dietary Approaches to Stop Hypertension) eating plan with some modifications. One diet emphasized carbohydrates, another diet emphasized protein, and the third emphasized monounsaturated fat. They reported that while all three diets lowered blood pressure, improved cholesterol levels, and reduced ten-year risk of heart disease by as much as 16 to 21 percent, two of these modified diets were even more effective in reducing some risk factors and estimated risk for heart disease than the diet richer in carbohydrates.
The Optimal Macronutrient Intake Trial to Prevent Heart Disease (OmniHeart) study will be presented today in Dallas at the American Heart Association annual conference, and also published in the November 15 issue of the Journal of the American Medical Association.
These new OmniHeart study results do not represent new guidelines for healthy eating and the proportions of carbohydrate, protein, and fat for all three diets are all within the ranges recommended by the U.S. Dietary Guidelines for Americans and other national public health organizations. Earlier in 2005, the U.S. Department of Health and Human Services incorporated NHLBI’s DASH eating plan as one option within the U.S. Dietary Guidelines.
All of the studied diets are a vast improvement over the typical American diet which can be high in saturated fat and low in essential nutrients, according to NHLBI Director Elizabeth G. Nabel, M.D.
“This study builds on an established body of evidence that shows following a dietary pattern lower in saturated fat, such as the DASH eating plan, can go a long way toward improving overall heart health. With these new data, we have been able to incorporate even more flexibility into the DASH eating plan by providing additional options for people seeking to improve their heart health through healthier eating,” said Nabel.
The study results reinforce the health benefits of following a DASH-type eating plan and suggests that tweaking certain components within that plan—protein and unsaturated fat—may yield benefits for specific risk factors. Compared with the study diet containing more carbohydrates, the diet with greater protein:
* lowered blood pressure, LDL “bad” cholesterol, and triglycerides, and
* lowered HDL “good” cholesterol.
The diet with more unsaturated fat, primarily monounsaturated fat:
* lowered blood pressure and triglycerides,
* raised HDL, and
* did not lower LDL.
By providing all daily meals to 164 men and women for 41 days for each diet, researchers evaluated the three diets to determine whether replacing calories from saturated fat with calories from protein or unsaturated fat was better than replacing those calories with carbohydrate. Saturated fat is known to raise blood cholesterol, and public health officials recommend that it make up less than 10 percent of daily calories for healthy individuals and less than 7 percent of daily calories for individuals with heart disease risk factors.
Participants were age 30 or older and had either high blood pressure or prehypertension at the time of enrollment.
“These new findings open the door to further research on the diets’ long-term effects and the ability of people to follow these diets,” said Eva Obarzanek, Ph.D., NHLBI research nutritionist and study co-author.
The OmniHeart study diets differed from each other in several ways:
* The diet emphasizing carbohydrates contained 58 percent of calories from carbohydrates and 15 percent of calories from protein. In addition, it contained 21 percent of calories from unsaturated fat. The other two diets reduced carbohydrate to 48 percent of calories.
* The diet emphasizing protein increased the protein to 25 percent of calories. To increase protein, mostly plant sources, such as beans and nuts, were used, although poultry, egg substitutes, and fat-free or low-fat milk products were also used. Like the carbohydrate diet, it contained 21 percent of calories from unsaturated fat.
* The diet emphasizing unsaturated fat used primarily fats and oils rich in monounsaturated fat, like olive oil, to increase unsaturated fat to 31 percent of calories. Like the carbohydrate diet, it contained 15 percent of calories from protein.
“Our results emphasize the impact that diet can have on blood pressure and cholesterol levels, two of the major heart disease risk factors,” said Lawrence Appel, M.D., M.P.H., of Johns Hopkins Medical Institutions and lead investigator of the OmniHeart study.
The OmniHeart study did not address other types of diets such as the Atkins or Mediterranean diet.
The OmniHeart study was conducted at Johns Hopkins Medical Institutions and Brigham and Women’s Hospital. The first participants started the protocol in 2003, and the last participants ended the study in June 2005.
NHLBI has long recommended changes in lifestyle, including following a heart healthy eating plan to reduce risk factors for heart disease. The DASH eating plan was developed through a series of clinical studies that showed that a dietary pattern rich in fruits, vegetables, fat-free or low-fat milk and milk products, and whole grains substantially reduced blood pressure and had other beneficial effects. The eating plan also includes lean meats, poultry, fish, legumes, and nuts and is low in saturated fats, cholesterol, sodium, and sweets and added sugars.
The new DASH Eating Plan menus are included in the book A Healthier You published by the U.S. Department of Health and Human Services. This newly released book is based on the 2005 Dietary Guidelines for Americans.