SAN FRANCISCO  Dark green chard plucked from a makeshift garden in front of City Hall; soft cheeses spread on freshly baked whole-grain bread and served in exhibition halls; farm-raised free-range chickens carved, seasoned and roasted.

Mix together. Yield: one revolution.

At least that is the hope of organizers of this weekend's inaugural "Slow Food Nation" convention, so named to represent the spectrum opposite fast foods.

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That means foods that are "delicious, wholesome, fresh" — and sustainably grown, says Alice Waters, owner of the world-famous Chez Panisse Restaurant in Berkeley and founder of Slow Food Nation.

About 50,000 people are expected to gather throughout the city for three days of lectures, concerts and, of course, meals. Events range from the free organic demonstration garden planted temporarily in front of City Hall to paid lectures by top authors and foodies to a demonstration on how to properly carve a chicken. Many sessions will be filmed and uploaded in a few weeks to YouTube, Waters says.

"This is going to be a coming of age of American food," Waters says. With epidemic rates of obesity, diabetes, global warming and ecological degradation, "we need a new food system in America. We need a new food system that supports the people who are taking care of the land, supports the small farmers, that feeds the children something that's nourishing."

Waters hopes many such events will spread to other American cities. The promoted foods are organic, wholesome and often a lot more expensive than processed fast food — a fact that has caused some to criticize the movement as elitist.

But people need to reprioritize food — much as they did in the 1940s before processed fast foods took over, says Slow Food Nation executive director Anya Fernald. "This is an event to birth a more political food movement. We're operating in a context where it's become blatantly obvious that we're eating ourselves to death in America."

But, she says, reprioritizing our food — putting it ahead of luxuries like cellphones and expensive shoes, perhaps — will not only be healthy. It also will be "joyous."

"We pay upfront to eat food that's good for us," Waters says, "or we pay out back in our health costs."