Avoid food products that make health claims. 

This sounds counterintuitive, but consider: For a product to carry a health claim on its package, it must first have a package, so right off the bat it's more likely to be a processed rather than a whole food. Then, only the big food manufacturers have the where-withal to secure FDAapproved health claims for their products and then trumpet them to the world. Generally, it is the products of modern food science that make the boldest health claims, and these are often founded on incomplete and often bad science. Don't forget that margarine, one of the first industrial foods to claim it was more healthful than the traditional food it replaced, turned out to contain transfats that give people heart attacks. The healthiest food in the supermarket - the fresh produce - doesn't boast about its healthfulness, because the growers don't have the budget or the packaging. Don't take the silence of the yams as a sign they have nothing valuable to say about your health.

Avoid food products with the wordoid "lite" or the terms "low-fat" or "nonfat" in their names. 

The forty-year-old campaign to create low-and nonfat versions of traditional foods has been a failure: We've gotten fat on low-fat products. Why? Because removing the fat from foods doesn't necessarily make them nonfattening. Carbohydrates can also make you fat, and many low- and nonfat foods boost the sugars to make up for the loss of flavor. Also, by demonizing one nutrient - fat - we inevitably give a free pass to another, supposedly "good," nutrient - carbohydrates in this case - and then proceed to eat too much of that instead. Since the low-fat campaign began in the late 1970s, Americans actually have been eating more than 500 additional calories per day, most of them in the form of refined carbohydrates like sugar. The result: The average male is seventeen pounds heavier and the average female nineteen pounds heavier than in the late 1970s. You're better off eating the real thing in moderation than bingeing on "lite" food products packed with sugars and salt.

Avoid foods that are pretending to be something they are not.

 Imitation butter - aka margarine - is the classic example. To make something like nonfat cream cheese that contains neither cream nor cheese requires an extreme degree of processing; such products should be labeled as imitations and avoided. The same rule applies to soy-based mock meats, artificial sweeteners, and fake fats and starches.

Avoid foods you see advertised on television. 

Food marketers are ingenious at turning criticisms of their products - and rules like these - into new ways to sell slightly different versions of the same processed foods: They simply reformulate (to be low-fat, have no HFCS or transfats, or to contain fewer ingredients) and then boast about their implied healthfulness, whether the boast is meaningful or not. The best way to escape these marketing ploys is to tune out the marketing itself, by refusing to buy heavily promoted foods. Only the biggest food manufacturers can afford to advertise their products on television: More than two thirds of food advertising is spent promoting processed foods (and alcohol), so if you avoid products with big ad budgets, you'll automatically be avoiding edible foodlike substances. As for the 5 percent of food ads that promote whole foods (the prune or walnut growers or the beef ranchers), common sense will, one hopes, keep you from tarring them with the same brush - these are the exceptions that prove the rule. Bogus health claims and faulty food science have made supermarkets particularly treacherous places to shop for real food, which suggests the next two rules.

Shop the peripheries of the supermarket and stay out of the middle. 

Most supermarkets are laid out the same way: Processed food products dominate the center aisles of the store, while the cases of mostly fresh food - produce, meat and fish, dairy - line the walls. If you keep to the edges of the store you'll be much more likely to wind up with real food in your shopping cart. This strategy is not foolproof, however, since things like high-fructose corn syrup have crept into the dairy case under the cover of flavored yogurts and the like.

Eat only foods that will eventually rot. 

What does it mean for food to "go bad"? It usually means that the fungi and bacteria and insects and rodents with whom we compete for nutrients and calories have gotten to it before we did. Food processing began as a way to extend the shelf life of food by protecting it from these competitors. This is often accomplished by making the food less appealing to them, by removing nutrients from it that attract competitors, or by removing other nutrients likely to turn rancid, like omega-3 fatty acids. The more processed a food is, the longer the shelf life, and the less nutritious it typically is. Real food is alive - and therefore it should eventually die. (There are a few exceptions to this rule: For example, honey has a shelf life measured in centuries.) Note: Most of the immortal foodlike substances in the supermarket are found in the middle aisles.

Get out of the supermarket whenever you can. 

You won't find any high-fructose corn syrup at the farmers' market. You also won't find any elaborately processed food products, any packages with long lists of unpronounceable ingredients or dubious health claims, anything microwaveable, or, perhaps best of all, any old food from far away. What you will find are fresh, whole foods harvested at the peak of their taste and nutritional quality - precisely the kind your great-grandmother, or even your Neolithic ancestors, would easily recognize as food. The kind that is alive and eventually will rot.

Eat foods made from ingredients that you can picture in their raw state or growing in nature. 

Read the ingredients on a package of Twinkies or Pringles and imagine what those ingredients actually look like raw or in the places where they grow: You can't do it. This rule will keep all sorts of chemicals and foodlike substances out of your diet.