Calorie intake may not be a major factor in causing death by heart disease, according to a study, which questions the efficacy of low-calorie foods marketed for weight loss.
Instead, losing excess weight and exercising may do more to ward off death from heart disease, say Dr Jing Fang and colleagues from the Albert Einstein College of Medicine in New York.
After a 17-year study on almost 9,800 Americans, the researchers concluded that expending energy through physical activity may be the key to cutting the risks of heart disease, rather than modifying the diet.
"The fact is that those who both exercised more and ate more nevertheless had low cardiovascular mortality," said Fang.
The research, published in this month's American Journal of Preventive Medicine, involved 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 US government.
Fang's group compared reports of physical activity, body mass index and dietary caloric intake to deaths from heart disease through 1992. Participants were grouped by their initial reports of caloric intake (low, middle, high), recreation exercise (least, moderate, most) and body mass index (normal, overweight, obese) - a measure of weight in relation to height.
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," said Fang. The difference in mortality rates was 55 per cent.
Eating less does not necessarily mean that people are thinner, while eating more does not have to translate into obesity, she added. 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 behavioural, socioeconomic, genetic and clinical characteristics," she said.
A focus on increased energy expenditure rather than reduced caloric intake may be the most practical outcome of this study, and may offer the most productive behavioural strategy by which to extend healthy life.