Oprah Winfrey has admitted playing a role in perpetuating diet culture during her career and said a dieting item from a 1980s show was one of her "biggest regrets".

The 70-year-old star - who has been ranked among the most influential women in the world - has been open about her struggles to maintain a healthy weight and attempts to lose weight.

In March she said "making fun of my weight was a national sport" for more than two decades.

In comments reported by NBC, Sky's US partner, the talk show host told a livestream and live audience: "I want to acknowledge that I have been a steadfast participant in this diet culture through my platforms, through the magazine, through the talk show for 25 years.

"I've been a major contributor to it. I cannot tell you how many weight loss shows and makeovers I have done and they have been a staple since I've been working in television."

But she admitted an item on a 1988 edition of The Oprah Winfrey Show was one of her "biggest regrets" when she rolled a wagon of fat on to the stage to represent the weight she had recently lost thanks to a liquid diet and exercise.

She had starved herself for months, she said, admitting that it "sent a message that starving yourself with a liquid diet and set a standard for people watching that I, nor anybody else, could uphold. The very next day, I began to gain the weight back.

"I own what I've done, and now I want to do better."

Winfrey was speaking on Thursday at an event organised by WeightWatchers, whose board of directors she joined in 2015, before saying in February she was leaving.

In 2016, she used an interview in the magazine O to reveal she had lost 12kg, sharing the cover with nine other woman to celebrate their "best body".

In the issue, Winfrey said, "It was my idea to share the cover with other women who are on the same journey that I am. My own struggles with the scale are well known. I've never believed in hiding them."

In December, she told People she had started taking a weight loss drug, saying she used it "as I feel I need it, as a tool to manage not yo-yoing.

"The fact that there's a medically approved prescription for managing weight and staying healthier, in my lifetime, feels like relief, like redemption, like a gift, and not something to hide behind and once again be ridiculed for."