does exercise really make us thinner?

I just got around to reading this New York magazine article questioning whether you can really lose weight through exercise. The author posits that you can’t, because exercise just makes you hungry and so you eat more. Personally I have found that I lose about two to five pounds while training for a marathon — not a lot considering how much I end up running.

On the other hand, I feel like I am still pretty fit and trim at 35, unlike many of my male peers who have developed a beer gut. Losing five pounds/marathon isn’t much, but I’ve run a dozen marathons, who knows what kind of belly I’d have if I didn’t run. (I remember when I had knee surgery in 2003, didn’t get any exercise for a month, and quickly gained 10 pounds).

And I remember the first few times I went to the NYC Marathon expo, it was a little surprising to see all these fit, trim people people walking about. You can def. tell who the runners are.

Residents of New York City, where you have to walk more than in most places, are also definitely thinner than residents of the Midwest …and studies have shown that residents of “high-walkability” neighborhoods are thinner than people in sprawling places:

The magnitude of the effect wasn’t trivial: A typical white male living in a compact, mixed-use community weighs about 4.5 kilograms (10 pounds) less than a similar man in a diffuse subdivision containing nothing but homes, Frank and his colleagues reported.

(Although a critic quoted in that story says this may be because of self-sorting, and in a study tracking 5,000 volunteers over six years, he found “zero or very close to zero” affect on weight over those who moved during the course of the study. However I would argue that a weight loss of “very close to zero” could still be significant over the course of a decade or two.)

That’s probably my feeling — that yes, exercise does make you lose weight, but in a subtle way. It has to be a lifelong habit; you’re not going to see much affect on weight loss in a couple months through exercise alone.

What the NY magazine author says about exercise making you hungry is definitely true, but I also find that hard running suppresses my taste for sweets.

One of the key paragraphs of the New York magazine article is this:

Ultimately, the relationship between physical activity and fatness comes down to the question of cause and effect. Is Lance Armstrong excessively lean because he burns off a few thousand calories a day cycling, or is he driven to expend that energy because his body is constitutionally set against storing calories as fat? If his fat tissue is resistant to accumulating calories, his body has little choice but to burn them as quickly as possible: what Rony and his contemporaries called the “activity impulse”—a physiological drive, not a conscious one. His body is telling him to get on his bike and ride, not his mind. Those of us who run to fat would have the opposite problem. Our fat tissue wants to store calories, leaving our muscles with a relative dearth of energy to burn. It’s not willpower we lack, but fuel.

Well, I, for one, am dubious. There’s been whole years in my life where I didn’t exercise regularly, in my teens and early 20s. Starting an exercise regimen was _hard_ and I think it went against my body’s impulse to stay on the couch. A body at rest tends to stay at rest. Once you get some momentum going it gets much easier.

UPDATE: Okay, I remember enough Psychology 101 and B.F. Skinner to know that howevermuch it seems true, the statement “I’m a runner because I chose to be a runner” is ultimately unsatisfying. Maybe half the population who exercises has some genetic predisposition to do so; there’s some genetic basis for most character traits. But the distinction the article tries to draw between Lance Armstrong’s “body” telling him to get on his bike and ride and his “mind” telling him the same thing is cockamamie as well. That distinction can’t be drawn.