In Defense of Food was one of the most important books to come along in years. Food Rules recasts much of the important information from In Defense of Food into 64 rules for selecting real food, eating in moderation, and getting off the Western diet.
While I thought In Defense of Food was already pretty accessible and easy to get into, Food Rules pares down the material even further, by relating eating to our daily lives and using simple, everyday language. Most of the rules are just one page in length and, in some cases, the rules are just a single sentence, as with #20, "It's not food if it arrived through the window of your car." It's likely that the streamlined book format and simple rules will allow Pollan to reach many new readers.
I don't know about the utility of Food Rules for those who've already read In Defense of Food. The book felt like a refresher to me and I will probably look to loan it to people who would not otherwise read the longer and (by comparison) denser In Defense of Food.