The reality TV contestant famously spoke about her battle with her weight in her autobiography Dying To Be Thin in 2009, when she claimed that she had overcome her body issues.
However, in a new interview with Heat, Grahame confirmed that she is back in the 11th institution and is battling the illness every day.
Grahame claimed that she relapsed after she had a bunion removed and was no longer able to exercise.
"As soon as I could, I started exercising to a ridiculous degree - but without increasing the food," she said.
"I have this phobia of having more than 400 calories at any one time. I can't allow myself to sleep if I feel I haven't done enough exercise. I don't sit down for two hours after I've eaten."
Grahame added: "I feel like a failure. I've written my book and said that I've beaten this illness, but now it's completely controlling me.
"I have to know where and when I'll be eating two days in advance so I can prepare myself mentally. It just completely controls everything. I'm tormented. All I think about is this regimented schedule."
Grahame found fame on Big Brother 7 and went on to star in her own E4 reality series Princess Nikki.
> Nikki Grahame 'Dying To Be Thin' interview
> Nikki Grahame is your Ultimate BB star