Exercise, Dieting Equally Effective in Reducing Risk of Heart Disease

Moderate exercise and curbing one’s eating habits are equally effective in reducing body fat and in modifying levels of cholesterol believed to play a pivotal role in coronary heart disease, a new study by Stanford University researchers indicates.

The study found that overweight men who ran 11.4 miles a week and others who cut their food intake by 20% experienced comparable reductions in body fat and improvements in cholesterol levels.

But only the exercisers had no loss of lean body mass, or muscle, leaving them stronger than the dieters. For that reason, experts say the study, published today in The New England Journal of Medicine, underlines the value of exercise in preventing heart disease.

The new study expands upon earlier findings that exercise can improve cholesterol levels. The researchers had wondered whether exercise itself, or simply the weight loss that resulted from it, was responsible for the improvements. They found that weight loss alone would accomplish the same end.

However, in an editorial accompanying the study, two epidemiologists report that there is growing evidence that physical activity protects against coronary death--although the role of one’s constitutional, or genetic, predisposition to fitness remains unclear.

Also unclear is the optimal quantity and intensity of exercise, the epidemiologists say. Because of the proven risk of cardiac arrest during and immediately after exercise, they endorse brisk walking for sedentary, middle-aged people.

“The Stanford trial is an important step toward understanding the role of physical activity and diet in weight loss,” the editorial states. “The correction of obesity in an affluent, sedentary society, however, should not focus on decreased (food) intake.”

Coronary heart disease, in which heart tissue is damaged by insufficient blood supply, is believed to affect about 5 million Americans. Atherosclerosis, a form of hardening of the arteries, is a leading contributor to about 700,000 heart attack and stroke deaths annually.

The Stanford study of 131 middle-aged men was intended to expand upon an earlier finding that exercise can improve cholesterol levels. Does weight loss account for the improvement, the researchers wondered, or is there something special about exercise?

To answer that question, participants were randomly assigned to three groups--exercisers, dieters and a control group. For a year, the exercisers ran regularly but did not change their eating habits, the dieters cut their food intake and the control group made no changes.

The dieters were told not to change the balance of carbohydrates, fats and protein in their diet, so it would be clear that any physiological changes came from reduced overall intake--not, for example, from cutting back on fats.

At year’s end, the dieters had lost an average of 15 pounds--significantly more than the exercisers’ 9-pound average loss. Both groups had lost similar amounts of body fat; the dieters had also lost some lean body mass, presumably muscle, researchers said.

Both groups also experienced similar changes in blood levels of cholesterol and triglycerides--two measures of heart-disease risk. Both substances have been linked to atherosclerosis, a type of hardening of the arteries implicated in heart attack and stroke.

Specifically, each group showed increased levels of high-density lipoprotein (HDL) cholesterol, the so-called “good cholesterol” associated with lowered risk of heart disease. Cholesterol attaches itself to lipoproteins, which carry it in the blood.

Each group also showed similar drops in triglycerides, fatty substances that can indicate heart disease risk. People with high triglyceride levels often have low levels of HDL cholesterol and high levels of undesirable low-density lipoprotein (LDL) cholesterol.

The researchers found no drop in LDL cholesterol levels in either group, possibly because the diet and exercise regimens were insufficient to trigger a change. However, elevated HDL levels may be as important as lowered LDL levels in preventing heart disease.

“Weight loss is certainly an important component of lipoprotein changes,” Richard B. Terry, a co-author of the study, said in a telephone interview. “And such weight loss will bring about these lipoprotein changes, whether by diet or exercise.”

However, Terry said that other findings not in the study show that the exercisers were more successful than the dieters in keeping off their weight. For that reason and others, the importance of exercise in weight loss and heart disease prevention was stressed.