Given the various brief conversations I've had with various people (including my esteemed flatmate) about people who are overweight, I found these two items of great interest. The first argues that neither are people in as much control of their body weights as is commonly suggested, nor is the link between weight and more general health inversely proportional until one gets into statistical outliers.  The second makes the (much more controversial) claim that one can draw some pretty good parallels between the way the public viewed homosexuality thirty years ago, and the way it views the fat today (in terms of defining the two states, and how they could be dealt with, rather than implying equivalency in the degree of hatred each group suffers). It's by no way a perfect fit, but a lot of the specifics line up quite well.
For further reading, the update to this post is pretty good. No way to piss a liberal off more than to point out they're acting like Ayn Rand.
 As a quick preemption, remember that "making one's lifestyle more healthy" and "losing weight" are NOT equivalent. The former can often lead to the former, but weight is a dependant variable, and not nearly so well correlated as many people think.