A new study has said that the key to weight loss may be from changes to diet rather than exercise.
For the study, researchers from Loyola University Health System and other centers compared African American women in metropolitan Chicago with women in rural Nigeria.
On average, the Chicago women weighed 184 pounds and the Nigerian women weighed 127 pounds.
Researchers had expected to find that the slimmer Nigerian women would be more physically active.
However, they found no significant difference between the two groups in the amount of calories burned during physical activity.
"Decreased physical activity may not be the primary driver of the obesity epidemic," said Loyola nutritionist Amy Luke, Ph.D., co-author of the study.
Physical activity has many proven benefits. It strengthens bones and muscles, improves mental health and mood, lowers blood pressure, improves cholesterol levels and reduces the risk of cardiovascular disease, diabetes, breast cancer and colon cancer.
However, the new study suggests that weight control might not be among the main benefits.
Richard Cooper, Ph.D., co-author of the study and chairman of the Department of Preventive Medicine and Epidemiology, said that people burn more calories when they exercise but that gets compensates by eating more.
"We would love to say that physical activity has a positive effect on weight control, but that does not appear to be the case," Cooper said.
The study included 149 women from two rural Nigerian villages and 172 African American women from the west side of Chicago and suburban Maywood.
Adjusted for body size, the Chicago women burned an average of 760 calories per day in physical activity, while the Nigerian women burned 800 calories. This difference was not statistically significant.
Diet is a more likely explanation than physical activity expenditure for why Chicago women weigh more than Nigerian women, Luke said.
She noted the Nigerian diet is high in fiber and carbohydrates and low in fat and animal protein. On contrary, the Chicago diet is 40 percent to 45 percent fat and high in processed foods.
The study is published in the September 2008 issue of the journal Obesity.