If you want to live longer, cut back on the white bread, eat more beans and use olive or canola oil. But not too much.
That's what scientists concluded in one of the most comprehensive studies of the effect of diet on heart health. The findings, announced yesterday, will help fine-tune the advice that doctors give patients interested in healthy eating.
Over the course of the three-year, $6 million study, researchers at Johns Hopkins and another institution fed 164 people three healthy diets that included plenty of fruits and vegetables and were low in saturated fats.
One diet included a "normal" proportion of calories from carbohydrates - about 60 percent. In the second, scientists replaced about 10 percent of the carbohydrate calories with protein from plants such as beans. In the third, they replaced the same proportion of carbs with healthy fats, such as those found in olive oil.
After participants spent six weeks on each diet, researchers found that their risk factors for stroke and heart disease - blood pressure, cholesterol and triglyceride levels - dropped significantly, but more so on the protein-rich and healthy fat diets.
The protein diet cut the risk of cardiovascular disease by 21 percent, and the healthy fat diet cut it by 20 percent. But even the original carbohydrate diet cut the risk factors by 16 percent.
"Our bottom line was that all three diets were healthy and all three had beneficial effects, but there was a slight edge to the higher protein and to the unsaturated fat diets," said Dr. Lawrence Appel, an internist and professor at the Hopkins school of medicine who led the study.
The research is part of a continuing effort to refine the dietary advice doctors give patients trying to minimize the risk of heart disease.
Unhealthy levels of saturated fats, trans fats, salts and high cholesterol have long been linked to high blood pressure and heart disease.
A federally funded study in 2001 found that diet could be as effective as some medications at controlling hypertension. In 1997, Hopkins physicians developed a diet designed to curb high blood pressure, known as Dietary Approaches to Stop Hypertension (DASH).
Although DASH lowers the damaging type of cholesterol, known as low-density lipoprotein (LDL), it also reduces levels of the protective high-density lipoprotein (HDL), the so-called "good cholesterol." And, it has little impact on triglycerides - another unhealthy type of blood fat.
Experts also have been divided on the roles of other nutrients in heart health, such as protein, whole grain carbohydrates and healthy fat. That prompted the study, known as the Optimal Macronutrient Intake Trial to Prevent Heart Disease (OmniHeart).
The report, co-written by Dr. Frank M. Sacks of the Brigham & Women's Hospital at Harvard Medical School in Boston, appears today in the Journal of the American Medical Association. Appel presented the findings yesterday at an American Heart Association conference in Dallas.
The authors say that if the protein or healthy-fat diets were widely adopted, for every 100 people with mildly high blood pressure, there would be one less heart attack over 10 years, compared to the more carb-friendly diet.
Experts say the study also confirms what nutritionists have been saying for years: You can reduce your risk of heart disease by cutting back on the saturated fats found in meats and dairy products, as well as the trans fats in many cookies and candies.
The results also show that the unsaturated fats found in olive and fish oils are beneficial, they say.
"There was always this insistence on saying low fat, low fat, low fat. But, we now know that it's certain types of fat that we need to pay attention to. This study confirms that," said Alice Lichtenstein, a nutrition expert at Tufts University School of Medicine.
Other experts said that while people are interested in heart health, they have a difficult time changing behaviors, particularly when it comes to diet and exercise.
"The main thing is, choosing a diet you can live with and incorporating some type of physical activity into your daily routine," said Meir Stamper, a Harvard epidemiologist who studies obesity.
The study was funded by the National Heart, Lung and Blood Institute, a division of the National Institutes of Health.
All three diets used in the study required participants to eat 2,100 calories a day. The original carbohydrate diet included foods like pasta and breads and was modeled after the 1997 DASH diet.
The other two diets replaced 10 percent of the carbohydrates in that diet with either protein or unsaturated fat.
The unsaturated fat diet used more peanuts, olives and canola oils in cooking and seasoning. Instead of regular margarine, for example, participants ate toast with an olive oil-based margarine.