One reason among many that I dislike 70s AOR bands like Led Zeppelin and Pink Floyd is that they're so fucking thin. Not an ounce of fat on any of them.
This may seem like a rather arbitrary objection. The surface explanation of hard living and amphetamines surely shouldn't be a problem. Or maybe it seems like jealousy, considering I'm rather overweight myself. But scratching the surface a bit I think the distribution of which genres contain fat performers and which ones don't forms an interesting pattern - one that's close to the idea of the counterpublic and which raises a whole lot of other fascinating questions.
Cheap Monday Jeans don't do pant sizes above a 36 inch waist, which honestly isn't much. Perhaps they reckon that tight pants look a bit, well, pants on overweight people, but on the other hand they're also making a concious choice: by not making their clothes in big sizes, they are able to exclude undesirable, unpopular fatties from among their customers. (It's certainly never going to be as controversial as trying to exclude other marginal groups. Bullying poor people who want to buy your clothes is also okay.)
Maybe it's not a huge deal, but it's fairly symptomatic of the current countercultural outlook. Here in Sweden, at least, you hardly see any fat emos or täbb, the way you used to see overweight pandas. And, just as significantly, the current generation of electro-based hipsters and fluo kids are dangerously lean-looking - unlike the preceding indie crowd, which idolised people like Daniel Johnston, Antony Hegarty and Beth Ditto. Interestingly, this comes together with a turn from the middle-class idolisation of indie to the upper-class idolisation of hipsterism...
Probably not a coincidence. The genres that have traditionally excluded fat people are the ones which have also excluded other marginal groups: they're straight, white, male, emphasising able-bodiedness, and so on. In genres like heavy metal, prog rock and hardcore punk, everyone is thin and buff. Walk around any "fashionable in-crowd area" in a city where the bourgeoisie are at play, and everyone is going to be thin. As are all their hip bands. Most of the truly manufactured mainstream is damned thin too.
So who gets to be fat in music? Well, "outsider" women and feminine men, like the ones listed above. Performers in gay culture-based genres, like disco. And musicians from ethnic minorities - to take the obvious example of African-American music, there's Solomon Burke, Baby Huey, the often chubby Aretha Franklin, onto Missy Elliott, Big Pun, Fat Joe, Rick Ross. In short: musicians from forced marginalised groups, that counterpublic, are the ones who are allowed to be fat.
The question is why. There's obviously a measure of intersectionality going on here, several different systems of oppressions interacting. One can, for instance, see it from the perspective of the powerful: allowing overweight or disabled artists to come forward from marginalised groups emphasises their otherness. One could also talk about the correlation between minorities and poor people, who are often symbolised in today's society by their obesity.
But I think there is also a more positive spin. I think marginalised groups can be remarkably tolerant of other marginalised groups, caricatures of gay-hating immigrants or whatever notwithstanding. Disco, that ultimate music of marginalised group plurality, accepted gays, women, black performers, ethnic minorities etc. etc. in a way no rockist or hipster genre has ever done. Since each identity is outsider in itself, it makes accepting other ones easier. In fact, the artists generally allowed to come forward by the mainstream white society are the very pretty ones - look at motown's old stable - whereas the fat and ugly performers tend to stay in their minorities.
One more possiblity: Simon Frith has suggested that those who end up being the most creative musicians are the outsiders, the ones that don't really fit in. Maybe having a complex system of marginalities simply increases that possibility?