A bit about nutrition from my favorite book about food.Excerpted from IN DEFENSE OF FOOD by Michael Pollan. Reprinted by arrangement with The Penguin Press, a member of Penguin Group (USA), Inc. Copyright (c) Michael Pollan, 2008.Food Science's Golden AgeIn the years following the 1977 Dietary Goals and the 1982 National Academy of Sciences report on diet and cancer, the food industry, armed with its regulatory absolution, set about reengineering thousands of popular food products to contain more of the nutrients that science and government had deemed the good ones and fewer of the bad. A golden age for food science dawned. Hyphens sprouted like dandelions in the supermarket aisles: low-fat, no-cholesterol, high-fiber. Ingredients labels on formerly two- or three-ingredient foods such as mayonnaise and bread and yogurt ballooned with lengthy lists of new additives — what in a more benighted age would have been called adulterants. The Year of Eating Oat Bran — also known as 1988 — served as a kind of coming-out party for the food scientists, who succeeded in getting the material into nearly every processed food sold in America. Oat bran's moment on the dietary stage didn't last long, but the pattern now was set, and every few years since then, a new oat bran has taken its star turn under the marketing lights. (Here come omega-3s!)You would not think that common food animals could themselves be rejiggered to fit nutritionist fashion, but in fact some of them could be, and were, in response to the 1977 and 1982 dietary guidelines as animal scientists figured out how to breed leaner pigs and select for leaner beef. With widespread lipophobia taking hold of the human population, countless cattle lost their marbling and lean pork was repositioned as "the new white meat" — tasteless and tough as running shoes, perhaps, but now even a pork chop could compete with chicken as a way for eaters to "reduce saturated fat intake." In the years since then, egg producers figured out a clever way to redeem even the disreputable egg: By feeding flaxseed to hens, they could elevate levels of omega-3 fatty acids in the yolks.Aiming to do the same thing for pork and beef fat, the animal scientists are now at work genetically engineering omega-3 fatty acids into pigs and persuading cattle to lunch on flaxseed in the hope of introducing the blessed fish fat where it had never gone before: into hot dogs and hamburgers.But these whole foods are the exceptions. The typical whole food has much more trouble competing under the rules of nutritionism, if only because something like a banana or an avocado can't quite as readily change its nutritional stripes. (Though rest assured the genetic engineers are hard at work on the problem.) To date, at least, they can't put oat bran in a banana or omega-3s in a peach. So depending on the reigning nutritional orthodoxy, the avocado might either be a high-fat food to be assiduously avoided (Old Think) or a food high in monounsaturated fat to be embraced (New Think). The fate and supermarket sales of each whole food rises and falls with every change in the nutritional weather while the processed foods simply get reformulated and differently supplemented. That's why when the Atkins diet storm hit the food industry in 2003, bread and pasta got a quick redesign (dialing back the carbs; boosting the proteins) while poor unreconstructed potatoes and carrots were left out in the carbohydrate cold. (The low-carb indignities visited on bread and pasta, two formerly "traditional foods that everyone knows," would never have been possible had the imitation rule not been tossed out in 1973. Who would ever buy imitation spaghetti? But of course that is precisely what low-carb pasta is.)A handful of lucky whole foods have recently gotten the "good nutrient" marketing treatment: The antioxidants in the pomegranate (a fruit formerly more trouble to eat than it was worth) now protect against cancer and erectile dysfunction, apparently, and the omega-3 fatty acids in the (formerly just fattening) walnut ward off heart disease. A whole subcategory of nutritional science — funded by industry and, according to one recent analysis,* remarkably reliable in its ability to find a health benefit in whatever food it has been commissioned to study — has sprung up to give a nutritionist sheen (and FDA-approved health claim) to all sorts of foods, including some not ordinarily thought of as healthy. The Mars Corporation recently endowed a chair in chocolate science at the University of California at Davis, where research on the antioxidant properties of cacao is making breakthroughs, so it shouldn't be long before we see chocolate bars bearing FDA-approved health claims. (When we do, nutritionism will surely have entered its baroque phase.) Fortunately for everyone playing this game, scientists can find an antioxidant in just about any plant-based food they choose to study.Yet as a general rule it's a whole lot easier to slap a health claim on a box of sugary cereal than on a raw potato or a carrot, with the perverse result that the most healthful foods in the supermarket sit there quietly in the produce section, silent as stroke victims, while a few aisles over in Cereal the Cocoa Puffs and Lucky Charms are screaming their newfound "whole-grain goodness" to the rafters. Watch out for those health claims.