It is the latest diet fad, urging weight watchers to soak in ice-cold baths, give up fruit and gulp down black coffee before exercise.
The self-published ebook, Six Weeks To OMG: Get Skinnier Than All Your Friends, has knocked The Dukan Diet from the top of the bestseller list and secured its author a seven-figure book deal in the US.
But critics say the word-of-mouth hit, said to be inspired by reality TV show The Only Way Is Essex, cynically targets impressionable teenagers.
Nutritionists and parents say the 'quick fix' diet could herald an epidemic of eating disorders.
Psychologist Deanne Jade, of the National Centre for Eating Disorders, said she was horrified by the diet's premise. She added: "Teenagers will try anything. They'll sit in a cold bath for hours.
"This diet uses psychology against vulnerable young people and will encourage unhealthy competition to lose weight."
Mrs Jade warned that sitting in ice-cold baths can seriously damage the immune system and said drinking black coffee stimulates the adrenal system, leaching minerals and vitamins from the body and damaging the thyroid.
"You can lose weight in a million wacky ways. But you'll put all it all back on again and you may have damaged your body, brain and appetite control for ever," she added.
Dr Ian Campbell, a GP and weight loss expert, said: "My first thought is OMG! This book is encouraging extreme behaviour.
"Teens are very vulnerable to diet fads, especially quirky ones like this. The advice is hypothetically correct but in reality will have little effect on weight loss and some of the advice like taking ice cold baths can be very dangerous. This is a cynical attempt to sell huge numbers of books and I certainly wouldn't recommend it."
The book, written by a British sports scientist and celebrity personal trainer who goes by the pen name of Venice A Fulton - real name Paul Khanna - claims to use a mix of nutrition, biochemistry, genetics and psychology to help readers lose 20lbs (9.07kg) of body fat and reduce cellulite.
Khanna denies specifically targeting teenagers and says he would never urge anyone under 16 or who was still growing to diet.
A spokesman for Khanna said: "The reason Paul wrote the book is to cut through all the myths about dieting and change people's lifestyle for the better.
"If people get into healthy habits when they are young that's obviously a good thing, but that's not the primary aim of the book."
- DAILY MAIL