Keep this in mind the next time you're trying to decide what to buy at the grocery store to stay healthy: Too much of what's sitting on shelves today isn't really food. It's nothing more than "edible substances."

That's what best-selling author Michael Pollan told a sellout crowd during Wednesday night's California Lecture at Westminster Presbyterian Church, 1300 N St. The Knight Professor of Journalism at University of California, Berkeley, has won national acclaim for such books as "The Omnivore's Dilemma" and "In Defense of Food."

"What is food?" was just one of the questions Pollan addressed in a question-and-answer format led by California's food and ag czar, A.G. Kawamura. That such a question even needs to be asked is evidence that much of American eating has become a problem, Pollan said.

"When it comes to food, I guess I'm conservative. My definition would be the plants and animals and fungi that we eat," he said. "If you process (food) too much, it no longer deserves that title."

"In Defense of Food," Pollan's most recent book, explains that Americans have moved away from eating "products of nature" to products of food science. While Americans seem obsessed with nutrition, they have actually become less healthy in the decades that nutritional science has become big business, Pollan says.

During the talk, Pollan challenged premises Americans are currently operating under. The first, that "what matters in food is the nutrients," has led nutrition to become the country's new true religion. Nutrients, he pointed out, can't be seen by the people eating them.

"If what matters in food is invisible, you need experts to tell you how to eat. It's a little like religion: You need someone to help you navigate the unseen world," he said.

Another premise has led to the idea of "the satanic nutrient" or "the evil nutrient" -- currently things like trans fat and high-fructose corn syrup -- and "the blessed nutrient," which can describe fiber and anti-oxidants, he said.

Under that premise, "eating is a matter of avoiding the bad ones and gravitating to the good ones, " said Pollan.

Because of these ideas, people now have a different perspective on food. And that is, "When you eat, you're either ruining your health or saving it," he said.

In his lecture before nearly 1,000 people, Pollan also discussed "unsustainable," "mono-culture" industrial agriculture, which has led to high food prices and diseases being bred at feedlots; the limits of organic farming; and the need for many farming models to be in place when industrial agriculture breaks down.

Pollan said federal policy change is needed to combat some of the most critical problems. Federal incentives need to be changed to persuade farmers to grow more food people need and to focus on quality, rather than quantity, he said.

The government can reward farmers for diversifying and creating carbon sinks, while penalizing those who produce huge amounts of methane, Pollan said.

The Obama administration also should consider building year-round farmers' market venues, especially in inner cities, to stimulate local food economies and give people access to fresh produce, he said, adding that giving impoverished people vouchers for farmers' markets would also help.

Pollan believes Americans have not only given up healthy eating. They've also lost touch with eating's significant side benefits, which were recognized throughout civilization until recent decades, he said.

People no longer get pleasure from much of what they eat. They've lost an important way to establish their identities, including cultural identities, through food. And they've traded in that all-important bonding and community-building time that comes only during shared meals to eat in front of the TV or computer, at work or in the car, he said.

"We seem to have narrowed down the lens in this health obsession," Pollan said. "That would be fine if it made us healthy people. But it hasn't."