Study Analyzes Calorie Management vs. Exercise For Weight Loss

I was quite pleased to see this in the NYTimes (and shoutout to Somerset for sending it in!), what with all the talk about food and calories I do all day:

And in a just world, frequent physical activity should make us slim. But repeated studies have shown that many people who begin an exercise program lose little or no weight. Some gain.

To better understand why, anthropologists leading one of the new studies began with a research trip to Tanzania. There, they recruited volunteers from the Hadza tribe, whose members still live by hunting and gathering.

Providing these tribespeople with a crash course in modern field-study technology, the researchers fitted them with GPS units, to scrupulously measure how many miles each walked daily while searching for food. They also asked them to swallow so-called doubly labeled water, a liquid in which the normal hydrogen and oxygen molecules have been replaced with versions containing tracers. By studying these elements later in a person’s urine, researchers can precisely determine someone’s energy expenditure and metabolic rate.

The researchers gathered data for 11 days, then calculated the participants’ typical daily physical activity, energy expenditure and resting metabolic rates. They then compared those numbers with the same measures for an average male and female Westerner.

It’s long been believed that a hunter-gatherer lifestyle involves considerable physical activity and therefore burns many calories, far more than are incinerated by your average American office worker each day. And it was true, the scientists determined, that the Hadza people in general moved more than many Americans do, with the men walking about seven miles a day and the women about three.

But it was not true that they were burning far more calories. In fact, the scientists calculated, the Hadza’s average metabolic rate, or the number of calories that they were burning over the course of a day, was about the same as the average metabolic rate for Westerners.

The implication, the scientists concluded, is that “active, ‘traditional’ lifestyles may not protect against obesity if diets change to promote increased caloric consumption.” That is, even active people will pack on pounds if they eat like most of us in the West.

The underlying and rather disheartening message of that finding, of course, is that physical activity by itself is not going to make and keep you thin.

I’m curious about this part, here:

In fact, the scientists calculated, the Hadza’s average metabolic rate, or the number of calories that they were burning over the course of a day, was about the same as the average metabolic rate for Westerners.

…but… people with different body sizes burn different amounts of calories, so are we comparing the “slight” Hadza tribemembers (someoneplease tell me if that’s politically correct) with the “slight” Americans? If I were 5’9″ and 200lbs, and I run six miles in an hour, I’m going to burn way more calories than someone who is 5’9″ and 130lbs. The 130lb body doesn’t require as much energy to move the weight, because there’s not as much weight to move as there is in the 200lb body.

Dare I ask it, but are averages appropriate here?

And what about the body fat percentages of the Hadza tribemembers in comparison to the Americans?

And, what about the nutritional intake?

Do these variables still not matter in the minds of epidemiologists?

There is, however, one other part of the article that Ithought was very interesting:

“There’s this expectation that if you exercise, your metabolism won’t drop as you lose weight or will even speed up,” says Diana Thomas, a professor of mathematics at Montclair State University in New Jersey, who led the study.

But she says close mathematical scrutiny of past studies of exercise and weight loss shows that that happy prospect is, sad to say, unfounded. One of the few studies ever to have scrupulously monitored exercise, food intake and metabolic rates found that volunteers’ basal metabolic rates dropped as they lost weight, even though they exercised every day. As a result, although they were burning up to 500 calories during an exercise session, their total daily caloric burn was lower than it would have been had their metabolism remained unchanged, and they lost less weight than had been expected.

Now… I’ve said this twice – here, and here – but it bears repeating: your metabolism changes as you lose weight. Your ability to burn changes, as you lose. That’s why it’s so difficult to lose as you shrink in size.

What else did you spot in the coverage on this study? I know a few other places covered it and maybe they have different points they’ve highlighted… so let’s talk it out!