Mr. Pollan is not a biochemist or a nutritionist but rather a professor of science journalism at the University of California, Berkeley. You may recognize his name as the author of two highly praised books on food and nutrition, “In Defense of Food: An Eater’s Manifesto” and “The Omnivore’s Dilemma.” (All three books are from Penguin.)

Two fundamental facts provide the impetus Americans and other Westerners need to make dietary changes. One, as Mr. Pollan points out, is that populations who rely on the so-called Western diet — lots of processed foods, meat, added fat, sugar and refined grains — “invariably suffer from high rates of the so-called Western diseases: obesity, Type 2 diabetes, cardiovascular disease and cancer.” Indeed, 4 of the top 10 killers of Americans are linked to this diet.

As people in Asian and Mediterranean countries have become more Westernized (affluent, citified and exposed to the fast foods exported from the United States), they have become increasingly prone to the same afflictions.

The second fact is that people who consume traditional diets, free of the ersatz foods that line our supermarket shelves, experience these diseases at much lower rates. And those who, for reasons of ill health or dietary philosophy, have abandoned Western eating habits often experience a rapid and significant improvement in their health indicators.

Our economy cannot afford to continue to patch up the millions of people who each year develop a diet-related ailment, and our planetary resources simply cannot sustain our eating style and continue to support its ever-growing population.

In his last book, Mr. Pollan summarized his approach in just seven words: “Eat food. Not too much. Mostly plants.” The new book provides the practical steps, starting with advice to avoid “processed concoctions,” no matter what the label may claim (“no trans fats,” “low cholesterol,” “less sugar,” “reduced sodium,” “high in antioxidants” and so forth).

As Mr. Pollan puts it, “If it came from a plant, eat it; if it was made in a plant, don’t.” If you don’t have the time and inclination to read the first two, you can do yourself and your family no better service than to invest $11 and one hour to whip through the 139 pages of “Food Rules” and adapt its guidance to your shopping and eating habits.

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