If we can’t rely on the marketers or the government or even the nutritionists to guide us through the supermarket, then who can we rely on? Well, ask yourself another question: How did humans manage to choose foods and stay healthy before there were nutrition experts and food pyramids or breakfast cereals promising to improve your child’s focus? We relied on culture, which is another way of saying: on the accumulated wisdom of the tribe. (Which is itself another way of saying: on your mom and your grandma.) All of us carry around rules of thumb about eating that have been passed down in our families or plucked from the cultural conversation. Think of this body of food knowledge as samizdat nutrition: an informal, unsanctioned way of negotiating our eating lives that becomes indispensable at a time when official modes of talking about food have suffered a serious loss of credibility.