If I could be bothered I'd find sources for what I'm about to say but I really can't so Google it.
Fat was attractive most likely because food was scarce, it was a sign of wealth that you could afford all that food and gorge on it. When sugar was first introduced people ate so much their teeth rotted just to show they could afford to too. Now with food readily available it's shifted to thin. The reason we find certain things attractive lay in evolutionary psychology (and personal stuff also)
a hips to waist ratio of some 30%? not sure precisely is found attractive (child bearing hips and shows virility/health), having a symmetrical body is found attractive. Clear skin shows health etc crap like that that needs more studying to see why we find things attractive. So we see why people photoshop stuff to make them more attractive, because it sells, making the product with them look more attractive.
As for curvy or fat? Whatever, as long as they're happy but I don't think there are many who would rather be fat than skinny.
I think we should all just try and be healthy, it's hard to do but we should at least try, whatever body we get from that is fine.