“You can change the world with every bite.” So says the new movie Food Inc., now in theaters. I’m not so sure.

I’m sitting in my neighborhood Cosi. Just ordered a “gigante” Artic Latte and a fruit cup. Did I change the world? For better? For worse? Who knows? I ought to know because I pay more attention than most people can to the social, environmental and health impacts of the food business. I’m paid to do so. And I don’t have a clue—where the coffee in the Latte came from, where the fruit came from, or what the embedded energy or carbon footprints.

By all means, go see Food Inc. The movie serves up a provocative indictment of industrial food. It shows how our eating habits affect climate change, waste and energy. (The food processing and packaging business is one of the top five industrial users of energy in the U.S.) The film is entertaining and clever, as you’ll see if you watch this trailer And the visuals are eye-opening, even for those of us who have read Michael Pollan and Eric Schlosser, two stars of the movie. The trouble is, the politics, economics and science of Food Inc. are all a bit fuzzy.

Consider the argument that we can change the world by redirecting our consumer dollars. Gary Hirshberg, the founder and CEO of Stonyfield Farm, puts it this way:

The irony is that the average consumer does not feel very powerful. They think that they are the recipients of whatever industry has put there for them to consume. Trust me, it’s the exact opposite. Those businesses spend billions of dollars to tally our votes. When we run an item past the supermarket scanner, we’re voting.

Well, sure—conscious consumers and smart branding have built companies like Stonyfield, Ben & Jerry’s, Odwalla, Honest Tea, Kashi, not to mention Whole Foods. All are admirable companies that make good products (well, maybe not the ice cream) in responsible ways.

But when I go to the supermarket, even assuming that I’m willing to set aside my personal preferences, which I’m not, I don’t know whether to “vote” for Coke or Pepsi, Cheerios or Grape Nuts, grapes from Chile or grapefruit from Florida, local berries or organic ones from across the country.

It’s devilishly complicated, and the connections from farm to fork are opaque, as Food Inc. points out. As Schlosser says, quite rightly:

There is this deliberate veil, this curtain that’s drawn between us and where our food is coming from. The industry doesn’t want you to know the truth about what you’re eating because if you knew, you might not want to eat it.

So until we bring radical transparency to the supermarket shelf, we’re casting our “votes” blindly. And we’re a long way from radical transparency. (For a relevant discussion about that, read these excellent posts by Joel Makower and Daniel Goleman.)

Now, I know that we can help bring about change by buying more organic food, eating less meat, shopping at farmers’ markets and growing our own gardens—all excellent ideas. Pollan’s In Defense of Food is terrific on these issues, and he’s good in the movie, too. Even better is Joel Salatin, the owner and farmer at Polyface Farms in Virginia made famous by The Omnivore’s Dilemma. He says:

Imagine … if, as a national policy, we said we would be successful only if we had fewer people going to the hospital next year than last year? The idea then would be to have such nutritionally dense, unadulterated food that people who ate it actually felt better, had more energy and weren’t sick as much…now, see, that’s a noble goal.

Yes, but changing “national policy” is not about consumer choices but about politics: Ending the subsidies that make empty calories cheap, requiring more transparency in the food system, as well as boring but important stuff like ensuring that the re-authorization of the Child Nutrition Act supports healthier choices in schools. (See Hungry for Change, part of the Food Inc. website.)

The movie is also confused about whether big is bad. Schlosser laments the fact that the meat industry is controlled by a handful of big companies and he doesn’t like McDonald’s, but McDonald’s is way ahead of other fast-food companies when it comes to sustainability; while that may not be saying much, fast food isn’t going away  so we’d best  encourage Mickey D’s to keep at it. The movie doesn’t like Monsanto or its genetically-engineered seeds, but it’s not clear how we are going to be able to feed 6 billion people without making agriculture more productive; biotech seeds may be part of the answer. Meanwhile, Wal-Mart wins (deserved) praise from Gary Hirshberg and as the movie notes, many of the “green” success stories in the food business have been swallowed by big companies Coca-Cola (Honest Tea, Odwalla), Kellogg (Kashi), Unilever (Ben & Jerry’s) and Group Danone (Stonyfield). So is big business the enemy when it comes to making food and agriculture more sustainable, or part of the solution. Probably, both, I’d say. Food Inc. isn’t sure.

To be sure, it’s asking a lot of a movie to deliver answers to complicated questions, like how to fix the food system. At least Food Inc. asks the right questions and provokes thought. It’s one more reason why the American food industry is ripe for change.