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Michael Pollan is a food detective with a simple piece of advice: "Never eat anything your great-grandmother wouldn't recognise as food."

In his quest to reclaim food from corporations and nutritionists, the American author has killed wild pigs for proscuitto, planted persimmons and lemons in his "postage-stamp sized" California garden and spent years of his life tracing the food we eat from soil to plate.

"My father was a great indoorsman," he told a packed house at the Auckland Writers & Readers Festival yesterday. "He thought the importance of hunting was lost with the invention of the Great Steakhouse, so I was basically starting from scratch."

Every page of Pollan's best-selling exposé The Omnivore's Dilemma throws up new questions about the Western diet. Even organic food wasn't safe from his sleuthing - readers told him they didn't finish the book for fear their guilty consciences would see them starve to death.

The next book by the New York Times contributor and former editor of Harper's, entitled In Defence of Food, tries to solve the problem of what to eat in seven words: "Eat food. Not too much. Mostly plants."

The trouble, says Pollan, is that most of us eat in complete ignorance of where our food comes from. Doctors know the Western diet of refined grain, refined oils, lots of meat and very little fruit and vegetables is to blame for many diseases, so why not go back to what we ate successfully for thousands of years? His recipe for good eating includes not eating any ingredient you can't pronounce, not eating processed food with the nutrients added back in, and taking your dietary advice from cookbooks rather than nutritionists. Pollan was kind to the nutritionist who raised her hand with a question, but scathing of what he calls "nutritionism". Even the US Government food pyramid was shaped by lobbying from food producers.

"Even as my mother was feeding us sticks of margarine, she was saying, 'you know one day they're going to find out butter is better for you'," he said, of his childhood before damaging trans-fats were found in margarine. "You know they're going to get it wrong again."

Pollan attacks the idea that food should be fast, cheap and easy, saying time spent in the garden and kitchen changes our relationship with food. "The cook doesn't need to be told that mixing olive oil with the tomatoes helps bring out the lycopene.

"The chef already knows that that is a very good idea."

By the end of his latest book, Pollan had hunted and gathered himself a meal he could eat with a clean conscience. "I understood precisely the sacrifice of life and effort that was involved in making it."