The end of the obesity epidemic

I have a piece in TNR on the new JAMA study finding no statistical change in obesity rates over the past decade in either adults or children. (The finding that got the most headlines was a 40% drop in “childhood obesity” among 2-5 year olds, but for reasons I explain in the article this finding is probably not very meaningful in and of itself).

On a related note, here is a review of Michael Gard’s important book The End of the Obesity Epidemic (A version of this review appears in Critical Public Health):

In recent years, medical researchers and public health authorities from all across the world have issued a series of alarming statements and predictions about the supposedly devastating health consequences of increasing body mass. These included claims that higher than average weight was the direct cause of hundreds of thousands of annual deaths in the United States alone; that within a few decades the entire populations of some developed countries would be overweight and obese; that, as a consequence of increasing weight, today’s children would have shorter life spans than their parents; and that the so-called obesity epidemic was a greater threat to societies than global warming.

Such statements have been picked up by politicians, who have characterized the situation as a public policy crisis, and who have called for intensive public health interventions. For example, Michelle Obama, the wife of American president Barack Obama, has made childhood obesity her signature issue, while heading a campaign with the explicit (and, scientifically speaking, preposterous) goal of “ending childhood obesity within a generation.”

Michael Gard’s The End of the Obesity Epidemic is, among other things, a thoroughgoing critique of the claims of those who could be called “obesity believers” (my term, not his). Gard is a self-described obesity skeptic, who sums up his own view of the matter thus:

I think we can now call the bluff of obesity science. The studies pointing to the ambiguous relationship between body weight, health, and mortality are piling up. Of course it is not healthy to be extremely fat, but the most important reason why there never was, nor will be, an obesity health crisis in the foreseeable future is because overweight and moderate obesity, in and of themselves, are neither diseases, nor particularly bad for one’s health. (p. 169)

Indeed, Gard emphasizes that each of what he calls “the four viral sound-bites” at the core of the panic over fat – the supposed massive death toll attributable to obesity, the exponential pattern of the “epidemic,” the shortened life spans of the next generation, and the parallel to the threat posed by anthropogenic climate change – “has been sustained by scarcely a whiff of scientific evidence.” Critical inquiry reveals that each of these claims is “an empty rhetorical shell . . . designed not to make a scientific case, but to create the impression of one.” (pp. 35-6).

But Gard’s book is not concerned primarily with debunking obesity alarmism. Building on arguments made in his earlier book with Jan Wright, The Obesity Epidemic, Gard’s new book considers many of the central claims of obesity believers to be so poorly supported that he sees no need to belabor the point. For example, he notes that the most significant aspect of predictions regarding future changes in average body mass “is that they are not based on any theoretical model or rationale.” Rather, “for obesity experts, the future must always be nothing more than a pale imitation of an arbitrarily chose moment in the past. This is much more folk superstition that it is science.” (p. 32).

Gard is focused instead on two inter-related aims: to undertake a kind of meta-critique of the various claims made by obesity believers and obesity skeptics, and to chronicle what he calls “the end of the obesity epidemic.” In regard to the first goal, Gard strives, in this context, to remain above the fray, emphasizing that, while he has his own views on these matters, what he wishes to emphasize here is the high level of uncertainty that still surrounds all sorts of basic questions touching on the relation between body weight and health, and in particular the tendency of both obesity believers and skeptics to deny this uncertainty.

Gard argues that researchers have not yet determined, even roughly speaking, the answers to a host of questions that one would think would have to be answered with tolerable certainty before undertaking the sorts of intrusive and expensive public health interventions recommended by obesity believers. Among these are:

*At what point, if any, does body mass and/or adiposity become a significant independent cause of mortality and morbidity? Is this point, assuming it exists, fairly consistent among individuals within the same cultural context, or across such contexts?

*Would making fat people significantly thinner improve their health, and is there any way of producing such a result through public health intermediation?

*Why did the populations of developed countries become heavier over the last quarter of the twentieth century, and why has this trend apparently stalled or even reversed in the years since? For instance, what were the relative contributions of increased caloric intake and decreased activity levels to increasing weight around the world, and what contribution have decreased or at least no longer increasing caloric intake, and/or increased or no longer decreasing activity levels, played in what Gard calls the end of the obesity epidemic?

The book’s caveats that the answers to these questions remain unknown are well taken, especially given that the central claims of obesity believers – claims which, as Gard chronicles, have taken on the status of received truths among many policy makers – depend on the assumption that we do in fact know the answers.

Gard’s most acerbic and amusing observations are aimed at obesity researchers who equate rising obesity rates to global warming, and who argue that, as in the case of climate change, the threat posed by the phenomenon is so serious that drastic ameliorative steps should be taken even, in the words of Harvard Medical School professor David Ludwig, “before all the scientific evidence is in.” Gard points out that there is no reason to believe that obesity researchers have any particular expertise in making judgments about how bad of a problem climate change actually is. Furthermore, he notes that even the most pessimistic experts on the topic agree that “predictions about the planet’s future climate are subject to a wide margin of error” — a circumstance which makes the analogy between global warming and obesity even more awkward and ironic, given the remarkably confident assertions obesity researchers make regarding both the seriousness and the likely future consequences of their pet problem. (p. 20)

Gard’s point here is not, I think, to call into question the seriousness of climate change as a public policy problem, but rather to emphasize how scientists and policy makers are prone, in their eagerness to bring attention to whatever purported crisis they are publicizing, to draw highly dubious analogies between very dissimilar subjects.

The book also devotes a chapter, co-authored by Gard and Carolyn Vander Schee, to demolishing the faith policy makers have, or at least claim to have, that the “obesity epidemic” can be solved, like so many other social problems and pseudo-problems, by having schoolteachers instill desirable habits in their students. Given the overwhelming evidence that such interventions do not work, Gard and Vander Schee suggest that the outsourcing of the “obesity crisis” to schools may indicate that many policy makers do not, in fact, take this supposed crisis very seriously after all.

The book’s thoroughgoing skepticism is not limited to the scientifically shaky claims of obesity believers. Gard devotes two chapters to critiquing the claims of various obesity skeptics. He divides dissenters from the public health orthodoxy regarding fat into what he calls empirical and ideological skeptics. Roughly speaking, this typology is based on his judgment that the former critics largely accept the standard scientific empirical frame in which arguments about obesity usually take place, and merely differ in their interpretation of the relevant data, while the latter critics undertake a more radical ideological critique of the whole idea of knowledge and truth as these concepts are understood in modern science in general, and contemporary medicine in particular.

Gard’s discussion of these issues is nuanced, and, as one of the “empirical skeptics” whose work he discusses in some detail, I found his critique thought-provoking, and some of his criticisms well-taken. A decade has passed since I wrote The Obesity Myth, and, if I were to write a similar book today, I would be less confident than I was then that we understand, for example, how much independent health benefit is derived from avoiding a sedentary lifestyle, or that, as I wrote then, “Americans are too sedentary” and eat too much “junk food.” Gard’s argument, in short, is that the empirical skeptics have not been skeptical enough regarding their own claims about the very complex relationships between weight, lifestyle, and health, and that their versions of obesity skepticism are prone to fall into the sort of “healthism” criticized by Robert Crawford and others, who emphasize what Gard characterizes as ideological skepticism. With the benefit of hindsight, I believe this is, at least in the case of my own work, a fair criticism.

The book’s most striking argument is that which gives the text its title. Gard assembles a host of data from several countries to demonstrate that, since around the turn of the century, rates of overweight and obesity have been flat or even declining, among both adults and children, across the developed world. The significance of this fact for the “war” on obesity can hardly be overstated. As Gard emphasizes, the dire predictions made by obesity researchers and the policy makers they influence about the calamitous future health effects of a fat population have been based on the assumption that obesity rates would continue to climb. After all, given that life expectancy is at an all-time high and measures of overall health are, as even most obesity believers will concede, better than ever in those nations where the “obesity epidemic” has been most prevalent, predictions of a public health disaster caused by higher weight have by necessity turned on the assumption that this disaster would manifest itself in the future, when, as some bold employers of statistical extrapolation have proposed, everyone would be fat.

But what if this assumption turns out to wrong? Gard draws what ought to be an obvious conclusion:

If the phenomenon of flattening, and, in some cases, falling rates of overweight and obesity are a real finding, there is an inescapable conclusion: almost all past predictions about future rates of overweight and obesity, future costs of treating obesity-related diseases and the future impact of overweight and obesity on Western life expectancy must now be discounted. (p. 68)

In other words, the book’s title has a double meaning. The obesity epidemic may be ending, not merely in the sense that national populations in at least the developed world are apparently no longer getting heavier, but in the more profound sense that the recent epidemic of scientifically dubious claims built around the assumption that rates of overweight and obesity would continue to climb should recede. As the evidence continues to build that higher body weight has at best a tenuous correlation with increased risk of death and disease, and that body mass is not inexorably increasing in the modern world, the moral panic over fat ought to continue to lose both its academic supporters, and its cultural and political influence.