Lady Gaga was hospitalised six times last year due to problems with her diet, it's been reported.

The singer's ex-tour manager David Ciemny claims in a new book that the singer frequently went on crash diets.

“When I say she was sick, I mean physically and mentally,” he says in the book, entitled Poker Face: The Rise and Rise of Lady Gaga.

Written by Maureen Callahan, the unofficial biography claims to be “the first in-depth biography of the extraordinary cultural phenomenon that is Lady Gaga”.

It features interviews with friends, employees, rivals, and music industry veterans.

An exert from the book, which has been serialised in today's Sun newspaper, also claims that there was “pressure” on the star to lose weight.

It also apparently lifts the lid on Lady Gaga's mental state, including the suggestion that she hired someone to accompany her at all times on tour.

Poker Face: The Rise and Rise of Lady Gaga is released later this month.

Lady Gaga is currently on the latest North American leg of her Monster Ball world tour. She is due to release her new album in the new year.

(by Jason Gregory)