There are plenty of good health reasons for sedentary people to be more active, but new research suggests weight loss isn't one of them.

Investigators from Loyola University in Chicago compared 149 women from rural Nigeria with 172 African American women from two Chicago-area neighborhoods and found no difference in activity-related energy expenditure between the two groups. This was surprising, given that the urban subjects were significantly heavier (184 lbs vs. 127 lbs) than their Nigerian counterparts and were much more likely to be obese (50% vs. 7%).

'We would love to say that physical activity has a positive effect on weight control, but that does not appear to be the case...'

"We would love to say that physical activity has a positive effect on weight control, but that does not appear to be the case," said Richard S. Cooper, PhD, chairman of preventive medicine and epidemiology at Loyola and a co-author of the study.

The findings, published in the September issue of Obesity, add fuel to an ongoing debate among nutrition researchers as to the relative contributions of energy expenditure (physical activity) versus energy intake (food consumption) to weight gain and obesity. Although the Loyola research team and their fellow investigators in Ibadan, Nigeria, have not yet done a detailed comparison of the Nigerian and American diets, the former is typically high in fiber and carbohydrates but low in fat and animal protein, while the latter is typically high in fat and processed foods.

A second Loyola study, published in the January issue of the American Journal of Clinical Nutrition, further analyzed the same populations and found that activity-related energy expenditure did not influence the amount of weight gained or lost during a three-year period. Although previous studies have suggested that higher levels of physical activity help prevent weight gain, those studies utilized questionnaires to estimate physical activity levels. The Loyola researchers measured energy expenditure using the more accurate, doubly-labeled water method, in which water molecules are labeled with an isotope that can be tracked throughout the metabolic process after study subjects drink the water.

"Evidence is beginning to accumulate that dietary intake may be more important than energy expenditure level," said Amy Luke, PhD, an associate professor of preventive medicine and epidemiology at Loyola and co-author of the study. "Weight loss is not likely to happen without dietary restraint."

But don't expect the U.S. government to decrease its recommendation of at least 2.5 hours of moderate activity or 75 minutes of vigorous activity per week. Regardless of its effect on weight loss, regular physical activity has been shown to protect against a number of health risks, including diabetes, cardiovascular disease, osteoporosis and certain cancers.