I read somewhere that in general, historically a societies' view of being fat was generally tied to wealth, much in the way that fashion has been. That is, being fat was generally seen as positive, since it meant that one didn't have to labor in the fields or the shitpits or whatever. Similarly, fashion is also designed to showcase wealth. Impractical cuts for maximum movement, delicate fabrics, ornamentation, etc.

Currently the prevailing fashions in the Western world are designed to show that people have enough money to afford quality food, work out and take vacations or travel to places with enough sun to tan their skin. In Eastern countries, fashions follow a similar suit, but whitening creams are popular amongst both men and women, not to look caucasian, but to show that they don't have to labor under the sun. Curiously, in Southeast Asian countries in particular, it is fashionable for only women to be thin (but not too thin), but it's ok for dudes to be fat as that's still seen as a sign of wealth. Also, minor deformities seem to be considered lucky, if gross. For example, prominent moles with long hairs are seen as particularly lucky (ick).

Anyway, while being fat might not be deadly, it is still unfashionable to be fat in the West. I'm not down with being cruel to fat people, but I am down with the current fashion of being physically fit. That said, I don't know too many high level athletes who live to 100. In fact, if I recall correctly, populations that have a lot of centenarians tend to be cultures where people tend to take it easy.