In the heavyweight event of the social calendar, more than 200 clinically obese people dressed in an oversized tribute to M&M sweets gather in Philadelphia for a Memorial Day ball. The participants listen to lectures on the evils of dieting, splash around in a hotel pool and watch a fashion parade aimed at those weighing more than 20 stone.

The annual event, organised by the National Association to Advance Fat Acceptance (Naafa), and sponsored by Mars, has become a rallying point for the militant wing of America's 38m large people, 2m of whom cannot see their own feet.

It is yo-yo dieting, Naafa claims, that poses the main threat to the health of the overweight. The group wants to ban most slimming pills and much corrective surgery.

"The pace of change is escalating," said a spokesman for Naafa. "In 20 years' time, dieting will be regarded as just as weird as Chinese foot-binding. That gives supermodels enough time to find another career."