Don't eat anything your great-grandmother wouldn't recognize as food. 

Imagine your great-grandmother (or grandmother, depending on your age) at your side as you roll down the aisles of the supermarket. You're standing together in front of the dairy case. She picks up a package of Go-GURT Portable Yogurt tubes - and hasn't a clue what this plastic cylinder of colored and flavored gel could possibly be. Is it a food or is it toothpaste? There are now thousands of foodish products in the supermarket that our ancestors simply wouldn't recognize as food. The reasons to avoid eating such complicated food products are many, and go beyond the various chemical additives and corn and soy derivatives they contain, or the plastics in which they are typically packaged, some of which are probably toxic. Today foods are processed in ways specifically designed to get us to buy and eat more by pushing our evolutionary buttons - our inborn preferences for sweetness and fat and salt. These tastes are difficult to find in nature but cheap and easy for the food scientist to deploy, with the result that food processing induces us to consume much more of these rarities than is good for us. The greatgrandma rule will help keep most of these items out of your cart.

Avoid food products containing ingredients that no ordinary human would keep in the pantry.

Ethoxylated diglycerides? Cellulose? Xanthan gum? Calcium propionate? Ammonium sulfate? If you wouldn't cook with them yourself, why let others use these ingredients to cook for you? The food scientists' chemistry set is designed to extend shelf life, make old food look fresher and more appetizing than it really is, and get you to eat more. Whether or not any of these additives pose a proven hazard to your health, many of them haven't been eaten by humans for very long, so they are best avoided.

Avoid food products that contain high-fructose corn syrup. 

Not because high-fructose corn syrup (HFCS) is any worse for you than sugar, but because it is, like many of the other unfamiliar ingredients in packaged foods, a reliable marker for a food product that has been highly processed. Also, highfructose corn syrup is being added to hundreds of foods that have not traditionally been sweetened - breads, condiments, and many snack foods - so if you avoid products that contain it, you will cut down on your sugar intake. But don't fall for the food industry's latest scam: products reformulated to contain "no HFCS" or "real cane sugar." These claims imply these foods are somehow healthier, but they're not. Sugar is sugar.

Avoid foods that have some form of sugar (or sweetener) listed among the top three ingredients.

Labels list ingredients by weight, and any product that has more sugar than other ingredients has too much sugar. (For an exception to this rule, see rule 60, regarding special occasion foods.) Complicating matters is the fact that, thanks to food science, there are now some forty types of sugar used in processed food, including barley malt, beet sugar, brown rice syrup, cane juice, corn sweetener, dextrin, dextrose, fructo-oligosaccharides, fruit juice concentrate, glucose, sucrose, invert sugar, polydextrose, sucrose, turbinado sugar, and so on. To repeat: Sugar is sugar. And organic sugar is sugar too. As for noncaloric sweeteners such as aspartame or Splenda, research (in both humans and animals) suggests that switching to artificial sweeteners does not lead to weight loss, for reasons not yet well understood. But it may be that deceiving the brain with the reward of sweetness stimulates a craving for even more sweetness.

Avoid food products that contain more than five ingredients. 

The specific number you adopt is arbitrary, but the more ingredients in a packaged food, the more highly processed it probably is. Note 1: A long list of ingredients in a recipe is not the same thing; that's fine. Note 2: Some products now boast, somewhat deceptively, about their short ingredient lists. Häagen-Dazs has a new line of ice cream called "five." Great - but it's still ice cream. Same goes for the threeingredient Tostitos corn chips advertised by Frito-Lay - okay, but they're still corn chips. In such cases, apply rule 60 for dealing with treats and special occasion foods.