What causes obesity? Advertising junk food to kids? Cheap soda? The demise of physical education in public schools? Too much screen time? Or maybe, it’s one of the little boxes in this Obesity System Influence Diagram, developed in 2007 by British researchers for their government’s Foresight Project:

Holy cow, I believe are the words you’re looking for. This is a lot different than the energy balance diagram we got when I was in college:

Clearly obesity is complicated. And that has turned out to be a good thing for folks who stand to lose money if we start trying to change the way people eat and move in this country.

In 2011, tasked with examining the effects of junk food marketing on childhood obesity, the Interagency Working Group (IWG), composed of representatives from the CDC, the FTC, the USDA, and the FDA, proposed recommendations for the food industry, urging companies to only advertise healthier foods to children. The response was swift and stern.

A public comment from PepsiCo in response to the recommendations read: “The IWG assumes, without any evidence, that there is a causal relationship between the marketing practices it proposes to banish and the problem it purports to solve.” A comment from General Mills asserted that “the inconvenient truth is this: There is no evidence to indicate that child-directed food advertising causes childhood obesity.”

In a comment addressing the proposed beverage taxes in California last year, a representative from the American Beverage Association wrote: “ …the soda taxes mentioned here [won’t] make any measurable difference when it comes to combating obesity.”

The food industry-funded website www.obesitymyths.com, among many other brazenly misleading statements, includes this one: “Myth: soda causes childhood obesity.”

Ignoring some pretty basic 3rd-grade-level inductive reasoning, the above statements are technically correct.

We have a good understanding of many of the things that influence obesity. Unfortunately, simply because there are so many things that influence obesity, it’s really hard to tell if fixing any one of them will have a significant impact on the problem.

Because of this, when public health policy makers attempt to address one of those factors that promote obesity, they often run into statements like those above, which can make passing health-promoting legislation difficult.

Dr. David Katz, director of the Yale-Griffin Prevention Research Center came up with a great analogy to illustrate this situation. From his website:

“Using multiple strategies to combat obesity is akin to stacking "sandbags" against a flood-tide. No one sand bag, however well made, can stop a flood. But stack enough sandbags, and you have a formidable protective barrier. We need such a barrier to protect us all from the flood of obesity-causing factors. No one program is the answer. But an array of thoughtful, practical, and well placed programs- can turn the tide!”

But what if policy makers weren’t trying to combat obesity in the first place? What if the IWG had framed its recommendations in terms of improving children’s eating habits, rather than moving a number on a scale? (The IWG recommendations were ultimately shelved after intense lobbying)

I called Dr. Katz to ask him whether he thought obesity is an appropriate target, in light of the difficulty in passing anti-obesity policies and measuring their impact. He maintained that on a population level, obesity is still a valuable surrogate for a host of health problems.

“The focus on obesity isn’t about weight. But it is a canary in the coal mine for all kinds of issues like diabetes, stroke, heart disease, dementia, cancer, etc. When we see obesity, we can be pretty sure that it’s more likely that a lot of these problems are going to follow, and as a doctor and public health professional, I can’t ignore that.”

Still, he said, with some health policies, we could be more clear about what the immediate goal is. For example, we know that soda consumption is related to a number of health issues and we know that these are empty calories that kids should not be consuming, he said. He pointed out that if we take soda machines out of school for the purpose of reducing obesity, then the American Beverage Association can come in and say “Look, this didn’t work.” However, he explained, if our target was the more proximal variable—reducing soda consumption, rather than reducing obesity, it could be a lot easier to measure success.

In some circles, we’re beginning to see a shift away from obesity prevention, particularly among groups advocating for reduced soda consumption. Their new targets? Type II diabetes and tooth decay. On the Alameda County Health Department website, www.sodafreesummer.org obesity is less emphasized than general health. One reason Berkeley’s recent penny-per-ounce tax on sugary beverages likely passed is expressly because its proponents never claimed it was meant to directly reduce obesity.

Last year I suggested that it might be more helpful for individuals to focus on behaviors rather than their weight. But maybe we could look into framing public health policies differently as well.

At a population level, BMI (a ratio of height to weight) is indeed a useful indicator of public health. As Dr. Katz pointed out to me on the phone, if we could shift the entire population toward a lower BMI, then we would see all sorts of health benefits.

But maybe, if we frame policies and campaigns as being geared towards improving diet and physical activity, rather than reducing weight, those policies would be more palatable, and their outcomes easier to measure. And then, even if shifting BMI isn’t the stated goal, as more people begin to eat better and move more, we’d see a healthier population that just also happens to weigh less.

Image credits: Shiftn, UConn Rudd Center for Food Policy & Obesity