I think we all knew it in our heart of hearts: size has superseded sex as the subject that is most on our minds. Currently, it is more mesmerising than all the old chestnuts: wealth, position, celebrity, scandal. We like to think we are still obsessed by all that stuff — that when we pore over the pages of a magazine, we are looking for pictures of rich, beautiful, famous people looking wretched because of their booze’n’pills problem, or fabulous on the arm of a married co-star. But all we really want to do is check out their BMI. We are that serious-looking one with the glasses on Celebrity Fit Club, only without the compassion or the healthy motives.

You name it: Oscar night, the big celebrity wedding, the daytime pap shot — all are just so many excuses to size up the shape that people are in (aka, how much weight they have gained or lost). Before the clothes, the hair, the unsuitable new boyfriend, our first thoughts are: “Look at her arms! It’s disgusting! It’s gorgeous! She has ballooned! Ohmigod, eat something!” Our people-watching has been reduced to one overriding concern: fatter or thinner?

Reese Witherspoon is going out with Jake Gyllenhaal (yes, but what’s happening in the body department?); Keira Knightley is starring in Atonement (whatever — look at those hip bones). The weight fluctuations of the rich and famous have become a spectator sport, scrutinised with the same intensity as Jonny Wilkinson’s injuries. There is even a whole stratum of celebrity that exists, as far as I can make out, exclusively to be fat-monitored: Knightley, Nicole Richie, Kate Bosworth. And then there’s another, the Friends Are Worried set, consisting of celebrities who are prone to dramatic shifts in BMI (Kirstie Alley, Sophie Dahl, Amy Winehouse).

But most astonishing of all, there exists a website (theskinnywebsite.com) devoted solely to updates on the precise loss/gain situation of any celebrity you care to think of. On Kelly Osbourne: “There is not much of a change to report. She still seems to be gaining weight at a steady rate.” Jessica Simpson’s update reads: “I don’t think she has gained significant weight back. Instead, it’s probably just the usual 5 or 10lb that she seems to go back and forth on.” Not a murmur about their whereabouts, latest projects, rumoured stints in rehab; just the water-retention analysis. Oh well.

Of course, the real issue here is the way it affects us. You can’t scrutinise a celebrity’s knee-area weight gain and then not notice your best friend’s bra bulge — and that way lies only misery. Start playing fatter-or-thinner in real life (“Ooh, you’ve lost weight”; “Oh no, I like you curvier”) and you have been got by the people who exist to make your life a tiny, ever-decreasing circle of pedicures, handbag purchases and fussing over the colour of your mobile phone. And we are much bigger than that.

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