As someone who has not been genetically blessed with a sylph-like figure, I know a thing or two about the uphill battle to lose weight.
The first week it's elation, when cutting back on that mid-morning doughnut sees you shed 1kg without even trying. The next few weeks you start doing wholly irrational things, like signing up to a three-year gym membership and filling your freezer with low-calorie lentil lasagne.
But as things grind on, you find it easier to justify eating that one little piece of black forest gateau, then spiral into a frenzy of guilt-induced gluttony that would have left Elvis feeling bloated. I have also known the Weight Watchers chub-reduction system - oh, so well. A good system, but one built largely around spurring you to lose your flab by weighing you publicly.
The whole group doesn't need to know your precise measurements, but the woman with the biro and the all-important record book does. And there's no way of fooling that lady if you've been a very bad, greedy girl since your last weigh-in.