Why do Americans eat junk food? Not because it’s cheap, Mark Bittman argued this weekend in the New York Times. A family could eat a meal of chicken, potatoes and salad for half the price of going to McDonald’s.

Time for cooking doesn’t look like an insurmountable obstacle, either: The average American watches over an hour of television each day. We eat junk food for two simple reasons: It’s easy and tastes good, often a lot better than healthful foods.

(David Paul Morris/GETTY IMAGES)

Bittman’s analysis is a great reminder to question assumptions often taken as fact in public policy debates. But public health research suggests that the policy recommendation that Bittman suggests won’t address our junk food addiction.

Bittman says we need to change our fast-food culture in the same way we tackled smoking -- making an unhealthy behavior taboo. “Obviously, in an atmosphere where any regulation is immediately labeled ‘nanny statism,’ changing ‘the environment’ is difficult,” Bittman writes. “But we’ve done this before, with tobacco.”

It’s a common comparison in the health policy world: We can intervene against unhealthy eating and halt our obesity epidemic the same way that public health campaigns have cut smoking rates in half over the past few decades. But in public health research, whether tactics to reduce smoking can also reduce poor eating habits is still a pretty open question.

One key difference between the two: Tobacco use poses a health threat to others via second-hand smoke, but obesity has no analogous menace to others. “While there are clearly huge economic costs associated with obesity that are born by society, there is no clear obesity counterpart to the harm caused by secondhand smoke,” Michael Erikson, editor-in-chief of the journal Health Education Research, noted in a recent issue.

Not only is smoking unhealthy, its also completely voluntary. Eating, however, is not. And that forces anti-obesity campaigns to deal with a relatively complex message: Stop eating unhealthy food, start eating healthy food, and understand the difference between the two.

“Tobacco consumption is not recommended, even in small quantities, as a regular part of one’s lifestyle,” Stan Dorn at the Urban Institute wrote in a recent paper comparing obesity and tobacco interventions. “By contrast, many foods that create obesity if eaten in large quantities are harmless or can even contribute to good health if they are eaten in small portions.” Healthy eating is a moving target, one that hinges on portion size and nutritional balance, which makes it a hard one for public health campaigns to hit.

It’s also too early to say that we’ve done this before with tobacco. To be sure, anti-smoking campaigns are a huge public health success story, with the number of Americans smoking dropping from 42 percent in 1965 to 20 percent in 2007. But, that still leaves us with 46 million American adults who smoke. Tobacco use remains the leading cause of preventable death, according to the most recent Center for Disease Control statistics. Decades of aggressive, well-funded public health campaigns still leave a lot of work to be done.

Tobacco is a good model in terms of what Bittman wants to achieve: a big change in American habits that could dramatically improve public health. And, parts of the anti-tobacco campaign could be applied to the anti-junk food movement, too: Michael Pollan suggests in a Nation article this week that food movements would be wise to get industry on their side, much like anti-tobacco campaigns did. But in terms of the challenge and the strategy, getting Americans to eat more nutritious meals will probably be a much more complex and slow-moving effort.