'I wouldn't have gone ahead with that serious decision had it not been an act of almost desperation.
'I had got to the point where I thought I have done everything I can to battle this weight. It won't shift. I could starve and it won't shift.
'The danger of yo-yoing again was very real so I had to do something pretty dramatic.'
She said she became interested in the operation after hearing that X-Factor presenter Sharon Osbourne had it done years earlier.
Miss Diamond, who lives in Oxfordshire, travelled to Belgium for the surgery after researching the procedure.
She wrote final letters to her four sons in case she suffered fatal complications during the operation.
Her confession, which can be seen on tomorrow's Celebrity Fit Club episode, could have seen her thrown off the series as a cheat.
However, the producers have decided to let her stay.
Fellow contestants, who include astrologist Russell Grant and actress Mikyla Dodd, have not all been so sympathetic, however.
In the programme, fellow contestant and newspaper columnist Carole Malone told her: 'It is disingenuous. We were not all starting on a level playing field.
'I think it's a bit of a cheat. You didn't own up to it. You were specifically asked if you had had surgery.'
Despite her drastic step, Miss Diamond is still struggling to lose weight.
Over the past week she has lost just one pound, having started the series five weeks ago clinically obese at 14st 9lb.
'The surgery isn't working as well as it should for me,' she said. 'I have had to earn every single pound I have lost on Fit Club.'
An ITV spokesman said: 'This matter was brought to our attention and so we discussed it with Anne. We have decided to allow her to continue with the show.
'The fact that she went to such lengths to tackle her weight problem is an indication of how serious this is for her.'
