We need to talk about your body mass index

Lionel Shriver rarely lingers over physical descriptions, with one great exception: she’s
 highly conscious of how much her characters weigh. Her most famous novel, We Need to
Talk about Kevin, is arranged as a series of letters written by the narrator to her husband,
who ‘weighed in at a pretty standard 165, 170’. Previous novels are populated by a ‘210-pound
bass player’ and a man who ‘loses a hundred pounds in six months’. Others ‘added five pounds’, ‘weighs little over a hundred pounds’, ‘dumped his full 160 pounds’, is ‘238 pounds by the age of 15’.
A woman ‘might have looked presentable if she had lost 20 pounds’, another is ‘at most
108 pounds’. Adjectives – ‘svelte’, ‘corpulent’, ‘broad-framed’, ‘wiry’ – must seem imprecise
 to Shriver. And if readers find it difficult to translate numbers into mental pictures, that’s
not her concern.
In her new book, Big Brother, the narrator (168 pounds) decides that ‘in fiction,
authors who do not immediately identify roughly how much a character weighs
 are not doing their jobs.’ So important is bodyweight to how people navigate
the world, so critical to how they’re seen by others, that ignoring it is an
omission tantamount to ignoring gender – maybe even worse, since, in real life,
 ‘especially when the subject in question is on the large side, many of us
probably detect “on the large side” even before determining large person of which sex.’ As Jane Austen is to wealth – telling us precisely how much Mr Darcy gets a year –
so Shriver is to weight.

source:

http://www.lrb.co.uk/v35/n12/deborah-friedell/love-the-eater