Ezra Klein, WaPo blogger and now food columnist, has, of late, been particularly dour regarding attempts to address obesity. His “Gut Check” piece today on the limited policy tools available to fight the obesity epidemic confirms it:

Over the past 50 years, however, some privileged humans have been faced with a largely novel problem: the consequences of too much food and drink. For a while, the primary impact seemed to be extra lumps of flesh, which had their downsides so far as mating went but, overall, weren’t too bad. But in recent years, the problem has become much worse. In particular, the modern, privileged human has developed such chronic ailments as diabetes and heart disease. Unlike acute starvation, these diseases kill slowly, painfully and, above all, expensively.

The consequences are not confined to the individual. As I write, Congress is considering an overhaul of the health-care system. But the concern isn’t health: It’s money. If trends continue, health-care costs will chew up 100 percent of the gross domestic product by the end of the century. And estimates suggest that half to two-thirds of that growth is coming from chronic diseases related to diet. We’re eating our way through the national budget.

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He goes on to consider two currently favored approaches: taxing junk food and labeling calories. The problem? Both may work, but both also have mild effects. One study indicated that a 10% tax might reduce consumers’ BMI by a mere 0.6% (to put that in context, a BMI of 30 is considered obese) while labeling might reduce a small percentage of meal purchases by 100 calories. While these reductions compound over time, they remain “blunt tools.” Klein clearly favors calorie labeling, but admits that even its potential is “highly speculative.”

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But this analysis dances around the fundamental question regarding obesity: What exactly does it mean to “solve” it. We are after all swimming in calories. We are destined to be Chub Nation no matter what we do. Our goal can’t possibly be to make every American male an Adonis and every female an Aphrodite. Indeed, as you will invariably hear in any discussion of obesity, BMI is a weak and imprecise measure — only used out of, ironically, convenience. The CDC sets the definition of obesity as a BMI of 30, e.g. a 5’9″ person who weighs just over 200 lbs. Right now, all we know is that we want fewer people with BMIs over 30 and as few as possible over 40 (the definition of “morbidly obese”). But how many exactly?

And as for money, we have new data that tells us an obese senior has annual medical costs between $1400 and $6000 higher than a non-obese senior. We know we can’t afford to treat 20% of the population for Type II diabetes — but, while they have higher rates, the obese are not the exclusive sufferers from “diet-related diseases” like heart disease, stroke, high blood pressure and some cancers. So how many obese people can we afford to treat? And what do I even mean when I say “afford”? Must we give up — to paraphrase health economist and Obama adviser David Cutler’s famous formulation — our flat-screen TVs?

The fact is that no one has really established the criteria for “victory.” That said, “victory” is the worst way of looking at the endpoint. It can’t be a War on Obesity — the obese will always be with us. It is about getting obesity to a manageable level. But no one (that I know of) has yet declared exactly what that level is.

No wonder Ezra isn’t optimistic. It’s hard to hit a target when you don’t know what it looks like or where it is. As a result, people tend to search for the largest, most diffuse, most dramatic effects in evaluating their weapons. But it may very well be that aggregating several, smaller effects will get us to a sustainable place. Or not.

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Ultimately, it’s the uncertainty that leaves us casting about for the perfect solutions. And — while I believe that if asked to choose among “x, y, z, 1, 2, or 3” policy solutions for obesity, the answer will likely be “all of the above” — I also believe that until someone can properly identify the target for our actions against obesity every policy proposal will appear to fall short.

Public health experts: Get cracking!