If this is true, then the reason why obesity appears to be so intractable is that we are using the wrong means to cure and prevent it. In other words, if it’s not caused merely by eating too much and exercising too little, then it’s no surprise that it is resistant to behavioral modification aimed at eating less and, as Dave says, boosting physical activity. I recently co-founded a non-profit, the Nutrition Science Initiative, with support from the Laura and John Arnold Foundation, to facilitate and fund well-controlled experiments that should be able to establish reliably which of these causal hypotheses of obesity is correct.
As for Dave, he challenges the intractability argument itself. By doing so, he can argue that behavioral modification for obesity works, provided it’s done correctly, which is the new twist that he is bringing to the subject.
In a follow-up post on CJR’s website, “Playing the study game,” Dave defends his position that obesity is not an intractable condition by referencing five studies that he says “come up with positive long-term weight-loss results.” In doing so, he provides the case study for lesson number two in reporting on health and medicine. This one should also engender a consensus, again at least in theory if not in practice: always read the articles before writing about them and committing anything to press. (And acknowledge, as Dave does, that other articles could easily have been cited making orthogonal points.)
It’s also a lesson in the ambiguity of evidence that may be unique to medical research. Doing rigorously well-controlled experiments is exceedingly expensive when humans are the subjects, and the ethical challenges are enormous as well. But they are what is necessary to establish reliable knowledge. Unfortunately, many medical researchers and journalists have come to rely on lesser evidence of the kind Dave references, and it’s simply not good enough.
Dave’s first reference is about the National Weight Control Registry (NWCR). This is a database of 10,000 individuals who have lost at least 30 pounds and then maintained that loss for more than a year. If I did that, at 6’2” and 240, my maximum weight, it would drop my BMI from 30.8, mildly obese, to 27 in the mid range overweight.) The NWCR reports that its members have lost an average of 33 kilograms and maintained that weight loss for more than five years.
This seems impressive and strong confirmation of Dave’s interpretation, until you take into account the point that Parker Pope makes in her article about this very database, which is that the NWCR is nothing more than a compilation of anecdotal accounts. Parker Pope quotes an obesity researcher from Yale (who happens to be obese himself, apparently intractably so) noting correctly that “while the 10,000 people tracked in the registry are a useful resource, they also represent a tiny percentage of the tens of millions of people who have tried unsuccessfully to lose weight. All it means is that there are rare individuals who do manage to keep it off.” And that is indeed all it means. It says nothing about how large or small a percentage of obese individuals can do this. It could be one in ten thousand or less. It could be one in two. We have no idea.
Of Dave’s three other references, one is a review article of behavioral weight loss programs in children that makes only the tepid claim that “limited evidence suggests” adolescents can maintain a weight loss of 4 to 8 pounds for a year. One is a study in adults claiming that two thirds of those who got intensive behavioral modification did indeed maintain at least a 20-pound weight loss for one year, but it then says “three- to 5-year follow-up studies showed a gradual return to baseline weight.”
The last reference reports that subjects who averaged a 65-pound weight loss over five months gained back all but 15 pounds after five years. This is a glass half full, half empty case. Dave apparently looks at the 15 pounds and says, this is reason to believe Parker Pope was wrong. Parker Pope, I suspect, and I would look at the 50 pounds regained as evidence that she was right.
Finally, Dave evokes the Look Ahead study, a massive trial predicated on the notion that maintenance of a five percent weight over ten years is clinically meaningful. Dave says he wouldn’t t be so quick “to dismiss a 5 percent loss as nothing to celebrate.” He calls it a “proof of concept, putting the lie to claims that we are genetically fixed to have a certain weight.”