You know, it occurs to me that the sites could do things differently and not ask for a number at all. How about a scale from 'Blows away in a strong wind' to 'Big, Beautiful and proud of it!', with everything in between? You could have your dreaded 'HWP' but also things like 'Could stand to lose a little weight' or 'Big boned' or 'Needs a sammich'. Everybody'd get the picture and people wouldn't have to lie as much.
I'd love to see somebody try it.