MAYWOOD, IL -- Reduced physical activity may not be the main culprit in the obesity epidemic, a study by Loyola University in Chicago finds. Instead, attention to dietary intake plus exercise may be the best formula to combat obesity.

Scientists compared the amount of calories burned during physical activity by 172 African-American women in Chicago to 149 rural Nigerian women. The Chicago women weighed an average of 184 pounds, while the Nigerian women weighed 127 pounds.

The researchers failed to find a significant difference between the two groups regarding the amount of calories burned during physical activity, though they originally expected the Nigerian women to be more active. Once the numbers were adjusted for body size, the Chicago women burned an average of 760 calories a day during physical activity, while the Nigerian women burned 800 calories.

"Decreased physical activity may not be the primary driver of the obesity epidemic," says Loyola nutritionist Amy Luke, a corresponding author of the study and associate professor in the department of preventive medicine and epidemiology at Loyola University's Stritch School of Medicine.

Instead, diet is the more likely reason the Chicago women weighed more than the Nigerian women, Luke says. She noted that the women in Nigeria have a diet higher in fiber and carbohydrates and lower in fat and animal protein. The women in Chicago typically eat a diet that is 40-45 percent fat, and high in processed foods.

"Evidence is beginning to accumulate that dietary intake may be more important than energy expenditure level," Luke says. "Weight loss is not likely to happen without dietary restraint."

Other research facilities involved in the study include the University of Ibadan in Nigeria, Howard University, Johns Hopkins Bloomberg School of Public Health and the University of Wisconsin.