America's ongoing food fight intensified Friday with the premiere of "Fed Up," a searing indictment of the role that food manufacturers, agribusiness and Washington play in the obesity epidemic. The documentary, executive produced by Katie Couric (who also narrates) and Laurie David (who also produced "An Inconvenient Truth"), is just the latest (and loudest) voice in the cacophonous debate about nutrition.

"Fed Up" won't be considered as much of a polarizing polemic as "An Inconvenient Truth." Unlike climate change, no one denies rising obesity. But the film's conclusion that sugar-laden processed foods feed the epidemic will likely be met by a big backlash from Big Ag, Big Food and Big Government.

And oh, yeah, Big Media, too. Like previous spoonfuls of policy medicine, targeting sugar will mean the terms "food police" and "nanny state" will be heard often on talk radio and cable.

Politicians will pile on, too. Sarah Palin, for instance, drank a Big Gulp during a CPAC speech at the height of hysteria over then-New York Mayor Michael Bloomberg's push to limit oversized sodas. "Fed Up" covers that moment, but is bipartisan in its criticism. It alleges that Michelle Obama's "Let's Move!" movement has been immobilized by big business. And it singles out Sen. Amy Klobuchar, D.-Minn., for her role in intervening on behalf of Minnesota-based Schwan Food Co. in a debate over pizza and school lunches.

The oncoming counterclaims are just the latest example of how it's difficult to discern what to believe — and do — about personal and public policies on nutrition. Be it coffee, red wine or entire food groups, even qualified sources send conflicting signals.

Sources motivated by profit do, too. And their amplification makes advocacy difficult.

"A big problem with public health interventions is that they are a few exposures relative to a constant onslaught from the food industry and from the entertainment media," said Marco Yzer, a University of Minnesota associate professor who teaches in both the School of Journalism and Mass Communication and the School of Public Health. Yzer realizes that not only do health messages get outshouted, but when they are heard, it's often a literal and figurative eat-your-peas message. "As a field, we have not learned enough from our colleagues in advertising. The typical approach is to overeducate," Yzer said, adding: "There is a mismatch between audience motivation and educator objectives, and still most health education work emphasizes negative consequences of unhealthy eating too much when we are wired to turn away from those threats."

In fact, regarding nutrition, knowledge isn't often power. "More information doesn't mean that people are more informed," said Yzer.

Dr. Donald Hensrud, chair of preventive, occupational and aerospace medicine at the Mayo Clinic in Rochester, agrees. "Knowledge doesn't equal a change in behavior. The industry has a lot more resources to send out the messages they choose," he said.

Indeed, Americans are sedentary at the table as well as the couch: Nutrition, just like exercise, is a hard habit to reset.

The repeating behavior may be because of the complex causes and conflicting claims, Hensrud said. "Nutrition seems relatively easy: 'Eat less, exercise more.' But all the factors influencing this seemingly simple equation are incredibly complex: the environment, external factors, different messages we are receiving, our internal signals from our brain, social factors, marketing, time, convenience. All of those things bombard us with different messages and it's very difficult."

Difficult may be an understatement. Unlike smoking's on/off switch, nutrition is more of a dimmer switch. People smoke or they don't. But everybody eats, and Hensrud said he's yet to meet the person with a perfect diet.

"Fed Up" may also describe how some feel about arguing over food, whose image has moved from scarcity to scary in just a few generations. It's dispiriting that the joy of breaking bread further fractures a divided society.

Yet regardless of the prescription, few doubt a cure is needed, especially since kids' life spans — and in some cases, lives — are at stake. Since no solution will be efficacious without truth, some advocates are willing to weather the pushback from vested interests.

"We try to take a more inclusive and positive role in moving the argument forward," said Hensrud. "But if the benefit to the population, in the judgment of people making the policies, outweighs the infringement on individual rights, we have to take the less popular view and expect to take some hits."

John Rash is a Star Tribune editorial writer and columnist. The Rash Report can be heard at 8:20 a.m. Fridays on WCCO Radio, 830-AM. On Twitter: @rashreport.