Because Dave, Parker Pope, and I take different approaches to the problem, the evidence we consider meaningful—and, of course, not all of it is, and perhaps not even most of it—is naturally different as well. Parker Pope argues that obesity is intractable based on common sense and some small, very well controlled studies (a fundamental requirement of good science). She concludes that that once we get obese, we’re pretty much stuck and public health advice and discussion should reflect that. She is implicitly challenging the kind of anecdotal accounts evoked by Dave himself (“most of us know people—friends, family members, colleagues—who have lost weight and kept it off for years by changing the way they eat and boosting their physical activity”) to make the argument that all it takes to be significantly less obese and stay that way is the right kind of behavioral modification and, well, maybe sufficient will power as well.

I agree with Parker Pope’s assessment about the intractability of obesity, but I argue that this is a product not so much of how the human body responds to weight loss but how it responds to the methods used to achieve that weight loss. I argued in my New York Times Magazine article that the old advice not to eat carbohydrates (refined grains and sugars, in particular) may have been the right advice and that these carbohydrates might be the fundamental causes of obesity.

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.

Gary Taubes is co-founder of the Nutrition Science Initiative, and the author of Why We Get Fat and What to Do About It (Knopf 2010) and Good Calories, Bad Calories (Knopf 2007). He’s a contributing correspondent for the journal Science, and the only print journalist to win the Science in Society Journalism Award of the National Association of Science Writers three times.