Today's stars are slim and toned, whittled to within an inch of their lives.

When pressed about their slimming secrets, celebrities often rave about their "good genes", their affection for junk food, or declare that their secret to staying thin is simply running around after their children.

But here's what you should know: a lot of them are lying.

They take drugs

When Lindsay Lohan was arrested on suspicion of drink-driving, police said they found cocaine in her pocket.

Paris Hilton recently admitted to U.S. talk show host Larry King that she takes Adderall for attention deficit disorder.

Both drugs are often used by women looking to lose weight. Hollywood's party girls always seem to have access to certain drugs known to help shed pounds.

Just about every female celebrity arrested - from Paris to Nicole, from Lindsay to Britney Spears - has had prescription Adderall in her handbag. It keeps you awake while killing the appetite.

During the filming of Cold Mountain, there were rumours that one famous actress on set ate only boiled eggs.

She would rise in the morning and eat one and then have one or two at the end of the day. That was her entire diet.

Paris Hilton caused a stir when she walked into New York restaurant Nobu recently.

When a waiter asked the heiress for her order, he was quietly told: "Mineral water."

In fact, over the course of her two-hour "meal", Paris took sips of water and Red Bull - she didn't eat a single bite.

And she's not alone. Super-slim Desperate Housewives star Marcia Cross was spotted dining at a restaurant a few years back with her now husband Tom Mahoney.

According to one eyewitness: "He ordered sea bass and prawns, but she just sipped fruit juice."

Then there's the master cleanse, otherwise known as the lemonade diet: water mixed with maple syrup, lemon juice and cayenne pepper.

Beyonce admitted following it for two weeks to drop one-and-a-half stone for the film Dreamgirls, and Jared Leto used it to shed the two stone he'd gained to play Mark Chapman in the film Chapter 27.

Britney Spears has never been shy about her love for junk food and engages in all kinds of behaviour to counteract her taste for Taco Bell.

She smokes, drinks coffee and Red Bull, has diet pills in her bag and takes Adderall. She has also been seen hitting all-night drugstores, shopping for laxatives.

They chain-smoke

Grey's Anatomy star Katherine Heigl looks to have lost a stone in the last year.

She may be following a healthy eating plan, but she appears to have a secret weapon - she smokes constantly.

A few days ago, the beautiful blonde was spotted having lunch in Los Angeles.

She ordered just a salad, but spent the meal chain-smoking.

Nowadays she is rarely photographed without a cigarette in her mouth, and when she isn't smoking, she is clutching a pack.

Supermodel trainer Gelband admits: "I had one girl who was living on Diet Coke and peanuts. She drank three to five Diet Cokes a day and ate a big bag of nuts. If she got hungry, she smoked.

Her eyes had huge bags under them and she looked wasted. When we tried to work out, we had to stop every five minutes. It was awful."

Paparazzi shots regularly show Hollywood's skinniest actresses, such as Renee Zellweger and Mary-Kate Olsen, sporting giant sunglasses and regularly coming out of Starbucks clutching gigantic cups of coffee.

This is a trend in Hollywood, where many believe coffee not only speeds up their metabolism but also keeps them from eating.

Peterson says: "I had one guy using a Nicorette patch, not to quit smoking but to stop food cravings! This is a ridiculous approach and definitely won't work."

Who can forget those photographs of a skeletal-looking Teri Hatcher jogging through Hollywood with weights in both hands and bones protruding-through her skin?

Actress Kate Hudson, in a quest to shed the five stone she gained while pregnant with son Ryder, admitted to working out up to three hours daily for three months.

To prepare for her role as the sexy Daisy Duke, Jessica Simpson worked out for two hours a day, six days a week.

He adds: "Forget trying to look like a celebrity - look at you.

The reality is, the girl that's ten pounds overweight but loves her body is winning against the girl who is underweight but hates herself.

"There's no straight guy in the world who knows the difference between a size 14 and a size 4."