Study: Exercise Won’t Cure 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, a member of the study team.

While it may be true that diet, not exercise, causes the obesity, it’s fallacious to conclude that exercise won’t make any difference. It just isn’t a factor in this example. You have two variables that affect weight (Calories in and Calories burned), and only see that one is different here. At the very basic level, it’s conservation of energy.

People burn more calories when they exercise. Thing is, they compensate by eating more, said Richard Cooper, 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,” Cooper said.

It’s not clear if this was tested in the study — there’s no mention in the story — so one doesn’t know if it was a crappy experiment or it’s crappy reporting.

The science du jour is physics of weight loss, which is useful for this time of year when some of us tend to act as sanctuary for some extra mass (those poor, persecuted cookies and brethren, seeking asylum)

Here’s my own The Physics of Weight Loss

Matt has just posted on the topic over at Built on Facts:

The Christmas Calorie

Calories and Climbing

54! Surely something that difficult would burn a lot more calories, you’d think. And it does. The immense effort you expend in climbing is mostly budgeted to different bodily processes. You have to move extra air in and out of your lungs. You have to circulate blood at a much higher rate. You have to process the complicated chemistry required to keep your muscles moving. All of these things take energy, and by the time the shoe meets the stair most of the energy has already been lost, eventually ending up mostly in the form of heat. Your body can’t afford to overheat and so you begin sweating to carry the excess heat energy away. All that energy had to come from somewhere, and it came from the food you ate. By the time you’re on the observation deck looking over Manhattan you’ll have used up a lot more than 54 calories.

As Matt notes in his posts, this is all about thermodynamics. Your body is basically a heat engine operating somewhere around 25% efficiency, so that 54-Calorie change in potential energy is going to require that you burn about 200 Calories of food.

(related: No Sweat)