The tired old adage, “You are what you eat,” acquires new life in Michael Pollan’s compelling book, The Omnivore’s Dilemma: A Natural History of Four Meals (The Penguin Press). Tracing our food back to its sources in feedlots and fields, Pollan convincingly argues that modern Americans are made of corn — and that this is a very bad thing for our health, our economy and our environment. Industrial agriculture, Pollan explains, depends on the mass production of corn, whose cheapness the government ensures with subsidies that benefit the farmer and the food processor alike. Used to feed cattle, chickens and even salmon, corn is the raw material for much of our meat and dairy. Alternately a sweetener, a stabilizer, a thickener and an oil, corn also features prominently in our processed foods. At bottom, our milk, eggs and meat are corn; our candy, chips and soft drinks are corn; even our condiments are corn.…