Elizabeth Kolbert, writing in the New Yorker, asks a simple question: Why are we so fat? The short answer -- We eat too damn much -- is unbefitting a proper New Yorker essay, and so we're served a long, fascinating look at the literature of "weight-gain" books that aim to explain how Americans gained more than a billion pounds in the last ten years. The most convincing answer I found is: Price and elasticity of appetite.