Physical Activity Is Not The
Only Culprit Among Obese
A recent international study fails to support the common belief
that the number of calories burned in physical activity is a key
factor in rising rates of obesity.
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. To their surprise, 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., corresponding author of the study in the September 2008
issue of the journal Obesity. Luke is an associate professor in
the Department of Preventive Medicine and Epidemiology at Loyola
University Chicago Stritch School of Medicine.
Physical activity is defined as anything that gets your body
moving. U.S. government guidelines say that each week, adults
need at least 2 ½ hours of moderate aerobic activity (such
as brisk walking) or 75 minutes of vigorous activity (such as
jogging). Adults also should do muscle-strengthening activities,
such as weight-lifting or sit-ups, at least twice a week.
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.
But Loyola research suggests that weight control might not be
among the main benefits. People burn more calories when they exercise.
But they compensate by eating more, said Richard Cooper, Ph.D.,
co-author of the study and chairman of the Department of Preventive
Medicine and Epidemiology.
"We would love to say that physical activity has a positive
effect on weight control, but that does not appear to be the case,"
The recent study included 149 women from two rural Nigerian villages
and 172 African American women from the west side of Chicago and
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
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. By contrast, the Chicago diet
is 40 percent to 45 percent fat and high in processed foods.
Results of the new study are similar to those of a 2007 study
of men and women in Jamaica. Researchers from Loyola and other
centers found there was no association between weight gain and
calories burned during physical activity.
"Evidence is beginning to accumulate that dietary intake
may be more important than energy expenditure level," Luke
said. "Weight loss is not likely to happen without dietary