Clearly this book is about food, but in a way it's more actually about human psychology, because the book reorganizes the question of nutrition into the true animal nature of the human. Why do we eat? Because our animal instincts compel us to eat for survival, and when the reader remembers that, they will see the tool with which the rest of the book is constructed: Animal instinct.
For the most clear instance of animal instinct, look at the part of the book when, after having visited the farms from which many fast foods supply their food chain, he visits McDonalds. He sees the problem quite clearly: given the intensity of the human instinct to eat, given the specific design of the fast food in question, and the way its history brought it to be so addictive and tasty—his animal instincts are perfectly unlikely to scrutinize the burger and fries, because he likes them too much.
But if he was being intellectually honest, pursuing nutrition from a biochemical perspective, than clearly, he is at odds with himself. Should he sacrifice the milieu of modern foods? The answer is in animal habit and routine. In a way, the answer of this book is another animal instinct: Adapt! He reminds his readers that obesity is not a free illness. He reminds his reader that heart disease is not a joke either, and now that the human animal has better information available about nutrition, his purpose remains clear: Encouraging the reader to be healthy and to focus on meeting the real animal needs of one's body.
