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.