In Defense of Food : An Eater's Manifesto by Michael Pollan

If I had to recommend one book to someone who wanted a readable critique of "the Western diet," this would be it. His history of health advice and fads and laws is enough to make anyone angry. The book isn't perfect (for example, I think he romanticizes native diets by neglecting to mention malnutrition issues and he doesn't distinguish between most processed foods and healthy processed foods, such as bagged salads) but it is very good.