I keep looking around me and thinking about body shapes of all things.
I am not a thin or narrow person. Even if I dieted I would never fit into a size 8 (or if I did, I would literally be bones) because my bones are rather wide. The most width-wise I could lose is about 2 inches. This is literally the right to left measurement, not the front to back. I could lose weight, but I think if I went anything below a size 12 (US) or 14(Au) I would look really ill. And having hip bones sticking out is not an attractive look (well, I don't think it is. Ribs are okay, hip bones not so much!)
It is interesting the number of people that obsess with their weight or size without actually thinking about their underlying bone structure. I know the whole big bones/small bones thing has gone by the wayside in general, but there is more to look at than that. If you look at the people that fit into small clothes sizes they generally seem to be very narrow people at the hips and shoulders. This means that they don't have the hip bones sticking out prominently but still fit into those sizes.
This is not to justify people, including myself, carrying too much weight, and not being healthy, but more a comment on how getting into a specific clothes size, or down to a specific weight can become and obsession, even if it means that people end up looking like they have gone too far.
So the long and short of it is this:
Each person has a weight that is perfect for them, and no doctor, no gym, no chart can tell them what that weight it is. It is the weight they look and feel best at. The weight they feel strongest and healthiest at. For every person this is different.
Anyway, this is me rambling very randomly.