That's pretty much the plot of Fat by Rob Grant, which contains some very good information on obesity and various other food-related health myths: one of the facts that stuck with me is the obvious-in-hindsight observation that (even in first world countries) it is massively more dangerous for your health to be underweight than to be overweight.
And both are massively more dangerous than being fit.
Related To: The Unfinished Mystery of the Shangri-La Diet and Missed Distinctions
Megan McArdles blogs an interview with Paul Campos, author of The Obesity Myth. I'll let anyone who is interest read the whole thing, but here's some interesting excerpts:
and