"I never could get bulimia because I just didn't have that mental state to go that far, but I always wished I could," she says.
"But that just shows you how dangerous and what place I got to. To wish you could have a mental illness to that level is a very serious place to get to."
Bulimia is an emotional disorder associated with poor body image and an obsessive urge to diet.
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Sufferers indulge in bouts of extreme overeating followed by self-induced vomiting.
When asked how she got into such a state, she replies: "My body and mind was in that place, but I couldn't actually act out to make myself sick."
As a result, Fergie's weight ballooned: "I then grew and grew and grew, because I couldn't do the final bit, because it just didn't seem to resonate with me."
Of her food addiction and public perception, she says: "People say to me: 'Oh you're too spontaneous, you do this' . . . I did not accept it for so many years and that was the persecution and that's why I tried to make myself as beautiful and thin as Princess Diana or Elle Macpherson."
"I tried and of course it never went that way."
Fergie, once cruelly nicknamed the Duchess of Pork, became the face of Weight Watchers in the US.
She credited her recent 20 kilogram weight loss to a diet of mayonnaise, tomatoes and mandarins.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.