AN EMBARRASSED Oprah Winfrey admitted that she has "fallen off the wagon" of healthy living, gaining 18kg to now tip the scales at 90kg.

In O magazine's January issue, the 54-year old detailed her struggles with a thyroid condition and how it sparked "a fear of working out".

"I look at my thinner self and think, 'How did I let this happen again?'... I'm mad at myself," she said.