Oprah Winfrey has changed "everything" to achieve her health and fitness goals.

The 69-year-old media mogul has lost more than 40lbs (about 18kg) in recent months and when asked what the key to her success has been, she revealed that she has had to make a change in all aspects of her life and has no intentions of going back.

Asked what she had been doing to achieve results, she told 'Entertainment Tonight' at the premiere of 'The Color Purple': "It's not one thing, it's everything. I intend to keep it that way."

Meanwhile, the former talk show host went on to pay tribute to late TV producer Norman Lear - who was known as the creator of shows such as 'One Day At A Time' and 'The Jeffersons' - following his death on Tuesday at the age of 101.

She said: "He was one of the grand gentlemen of our time. I've had so much respect for him, I've interviewed him multiple times.

"I mean, in the very beginning, the 70s, his shows are what started the conversation about race and justice - 'All in the Family', 'The Jeffersons' - in a way that America had not been prepared to [discuss] before."

Winfrey went on to claim that the "impact" of Lear will be felt across the next several generations as she insisted that even those who are unfamiliar with his work are already "experiencing the benefit" of what he did for television audiences across the US.

"His impact and his legacy will be felt for generations to come. Even people who are not familiar with his shows are experiencing the benefits of what those shows did for us as a culture."