In the first controlled diet study in families to evaluate why some people respond more favorably to diet modifications than others, researchers in the Center for Human Nutrition discovered that individual variation in response to a cholesterol-lowering diet is a familial trait.

"By studying response in families, we are able to show that 40% of variation in response to diet is due to shared genes and environment," said Dr. Margo Denke, an investigator in the Center for Human Nutrition and lead author of the study.

To evaluate familial response to diet, Dr. Denke, associate professor of internal medicine, along with research associate Ahn Nguyen and faculty associate in internal medicine Beverley Adams-Huet, studied 46 families over a two-year period. The study was published in The Journal of the
American Medical Association in December.

The families followed a margarine-based diet for five weeks. Then they switched to a butter-based diet for five weeks. The participants consumed specially formulated breads, cookies and other products made with either regular tub margarine or butter. While evaluating familial response to diet, the researchers discovered that the total body mass index also plays a major role in individual response to a cholesterol-lowering diet.

Heavier individuals who participated in the study had higher low-density lipoprotein levels and were less responsive to dietary change. The LDL cholesterol, or "bad" cholesterol, contributes to blockage in the blood vessels, which eventually may lead to the onset of a heart attack or stroke.

"You can't modify your genes, but your weight is an important modifiable factor that influences response to a cholesterol-lowering diet," she said.

Another finding suggested that substituting margarine for butter reduces the "bad" cholesterol levels in adults and children."Although differences in response to diet were observed, 80 percent of participants lowered their LDL cholesterol level on the margarine-based diet compared to the butter diet," Dr. Denke said. The study confirmed that a margarine-based diet is healthier and may reduce heart-disease risk compared to a butter-based diet. The adult study participants' LDL cholesterol levels were reduced by 11 percent (9 percent in children) when a margarine-based, cholesterol-lowering diet was followed. The "good" cholesterol, called high-density lipoproteins, remained constant.

"Consumers should take this study as another confirmation that regular tub margarine is better for you than butter," Dr. Denke said. For some time, she said, consumers have not known which to choose--margarine or butter-- because of concerns over trans-fatty acids found in some types of margarine. Trans-fatty acids are formed when liquid oils are converted into a semi-solid fat, which is more convenient to spread. Ten years of research has proven that trans-fatty acids raise LDL-cholesterol levels.

This research, she said, has pushed some consumers to choose butter over margarine. "But choosing butter instead of margarine is not a healthy choice. Butter contains far more saturated fatty acids than margarine, and butter, is, therefore, a potent cholesterol-raising fat," Dr. Denke said. The tub margarine used in the study contained only 7 percent trans-fatty acids, which is typical of most tub margarines.

Choosing a cholesterol-lowering diet has been a longtime recommendation of health-care professionals in an effort to curb the incidence of coronary heart disease--the leading cause of death in America. "High cholesterol levels work over decades to cause heart disease," she said. "Children consuming diets high in saturated fat have higher cholesterol levels and more coronary artery plaque buildup than children on low saturated-fat diets. A healthy diet has important long-term benefits.