Just my opinion but models with wider hips and bust, I think tend to not be as naturally thin (on a relative basis of course, and nothing wrong with that...they probably look better for stuff like VS!). Basically I think when someone looks gaunt or like they're starving in some places, but still normal or thicker in other places, they are probably restricting A LOT. But I agree with you that they probably all watch what they eat to some extent, but some probably do it in a more healthy way while others starve.
For example (and I LOVE her and think she's super beautiful), I don't think Elsa is naturally that thin because she looks like she has no body fat up top and in the abs, but her hips and thighs look almost a bit big relatively.
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Freja Beha, on the other hand, just looks naturally slim all the way and her body fat looks more evenly distributed. She doesn't look like she's working out like crazy or not eating to achieve her body.
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Thank you for your take on proportions! I'm currently 32/25/34 so I've always wondered. I agree that the super thin look isn't really in anymore these days...slim but fit seems to be the trend these days, which is great because it probably means everyone is eating more and exercising instead of wasting away.