Oprah discusses her thyroid issues.

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Oprah says turning 50 felt fantastic, as did 51 and 52. After celebrating her 53rd birthday, she began having health problems.

"I couldn't sleep at night. I started to have heart palpitations and some leg swelling," she says. "My doctor said, 'You need to get off of salt.' And I instinctively knew that it wasn't salt, and so I went from that doctor to another doctor to another doctor. By the time I'd been to the fourth doctor, I was on heart medication, I was on blood pressure medication and [medication] for heart palpitations."

Doctors didn't recognize that Oprah had a thyroid problem...but the viewers did. "Nobody showed me the e-mails until I started talking about this, but I had e-mails from viewers saying, 'Tell Oprah to check her thyroid because I think she has a thyroid problem,'" she says.

When she was finally diagnosed with hypothyroidism, Oprah says she fell off the weight loss wagon. "It was a fat sentence because I thought, 'Well, now it doesn't matter. I've got a thyroid problem. If I don't embrace hunger, everything I eat is going to make me fat anyway, and my metabolism isn't working, so I might as well just eat whatever I want. Okay. Fat wins,'" she says. "I felt completely defeated."