We've heard it all before. But in the past few months the smokescreen shielding the secret world of celebrity slimming has started to lift. It's being openly acknowledged that Hollywood is in the grip of a diet drug phenomenon.

They're on a the size zero pill; they're seeing this great new diet guru; they're working out; or they're really busy.

"Trainers like me laugh ourselves silly listening to celebrities talk about their diet and exercise routines," says Jackie Warner, the co-owner of Sky Sport & Spa in Beverly Hills.

"If you need to get your body seriously skinny in three weeks, it's going to be difficult the natural way."

But there's nothing natural about Celeb-land's latest take on the trend to be uber-tiny that has seen some of the world's highest profile women shrink to less than four stone.

Poster girls for this scrawny silhouette include Victoria Beck-ham, photographed at the recent fashion shows looking painfully gaunt, while in the U.S., the pack is led by Nicole Richie, Lindsay Lohan, Mischa Barton and now Kate Bosworth, seen this week looking skeletal at a Dazed & Confused party in illinois.