Exercise, not diet, may be best defence against heart disease

Despite widespread attention to diet, calorie intake may not be a major factor in causing death by heart disease, according to a 17-year study of almost 9,800 Americans.

Instead, losing excess weight — or not becoming overweight to begin with — and exercising may do more to ward off death from heart disease, say Jing Fang, M.D., and colleagues from the Albert Einstein College of Medicine in the Bronx, New York.

“The fact is that those who both exercised more and ate more nevertheless had low cardiovascular mortality,” says Fang. Expending energy through physical activity may be the key to cutting the risks of heart disease and living a longer, more healthful life, she says.

The study appears in the American Journal of Preventive Medicine.

The researchers studied data from 9,790 participants in the First National Health and Nutrition Examination Survey, a national study from 1971 to 1975 that was funded by the U.S. government. Fang’s group compared reports of physical activity, body mass index and dietary caloric intake to deaths from heart disease through 1992.

They grouped participants by their initial reports of caloric intake (low, middle, high), recreation exercise (least, moderate, most) and body mass index (normal, overweight, obese). Body mass index is a measure of weight in relation to height.

Overweight and obese participants, those who consumed fewer calories, and those who exercised less were also likely to be older, black, have a lower family income, less likely to have graduated high school, and more likely to have higher blood pressure and cholesterol levels than those who ate and exercised more.

During 17 years of follow-up, 1,531 participants died of heart disease. After adjusting for BMI and physical activity, caloric intake was unrelated to heart disease. Those who exercised more and ate more were both leaner and had less than half the cardiovascular disease mortality than did those who exercised less, ate less and were overweight.

“Subjects with the lowest caloric intake, least physical activity, and who were overweight or obese had significantly higher cardiovascular mortality rates than those with high caloric intake, most physical activity, and normal weight,” Fang says. The difference in mortality rates was 55 percent.

Those who eat less won’t necessarily be thinner, she says, and eating more does not have to translate into obesity. People who were overweight and exercised less at the start faced increased cardiovascular mortality, even if they ate less.

“This suggests that heart disease outcome was not determined by a single factor, but rather by a compound of behavioral, socioeconomic, genetic and clinical characteristics,” she says.

A focus on increased energy expenditure rather than reduced caloric intake may be the most practical outcome of this study, she says, and may offer the most productive behavioral strategy by which to extend healthy life.