I believe Barbie's shape is a product of factors having to do with scaling. If you take a normal, healthy woman with an attractive, figure, and make a scale model of her that is about a foot tall, it won't look right. Scale a barbie doll up to life-sized, and it will look freakish. The same proportions don't look the same in different sizes.
I believe the shape of the Barbie doll is a product of objective research to determine that shape which, at the size of a Barbie doll, will most look to a young girl the way she thinks an attractive woman should look.
We do, of course, then have the idea that this presents an unrealistic and unhealthy example for that girl to try to aspire to as far as her own figure; but I believe there are worse influences than this at work.
The fashion industry, as a whole, tends to gravitate toward models who are thin to the point of being unhealthy—occasionally to absurd extremes. I have only ever watched one instance of Victoria's Secret's annual fashion show, and that was the first, many years ago. There was one model that they used that was simply grotesque—tempting me to suppose that they obtained this model by going to Ethiopia, digging up the rotting corpse of some poor young woman who starved to death in the great famine that occurred there about a decade before, got a witch-doctor to animate that corpse into a zombie, dressed it up in lingerie, and paraded it around on the stage with the other models. It was really rather disgusting, I thought.
I later determined that the horrid skeletal undead thing that they used is named “Alek Wek”, and is actually from Sudan, rather than Ethiopia, and is allegedly a living human being, rather than—as it certainly appears—an undead zombie created from the corpse of a long-dead famine victim.
Here are a few pictures from the IMDB of this creature:
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It doesn't look nearly as grotesque in these pictures as it did in the Victoria's Secret show. Being more fully-dressed, you don't see how freakishly and sickly emaciated it is as well as you could seeing it wearing only skimpy underwear.
This creature is considered one of the top fashion models; being put forth as an image of what a beautiful woman should look like. I have no idea how it is even alive; there does not appear to be nearly enough flesh to sustain a living organism of its size. In any event, I am sure you can image the harm that any young girl would do to herself trying to conform to this notion of “beauty”. However it is that this creature has achieved this figure without starving to death, it should be obvious that most who attempt to do so would not succeed; and would die well before they achieved this degree of gauntness.