Oprah Winfrey buys ten per cent stake in Weight Watchers - stock prices soar

The celebrity and tycoon said she had a postive personal experience with the company

Winfrey is a significant influencer in the US and one estimate predicted that her endorsement of Mr Obama between 2006 and 2008 delivered over a million votes in the 2008 Democratic primary race (Getty)

The celebrity and businesswoman Oprah Winfrey has acquired a ten per cent stake in Weight Watchers International - sending the dieting company's stock soaring.

Winfrey, who is also getting options to acquire an additional five per cent stake, said she was joining the Weight Watchers board after a positive personal experience with the company's weight-loss programme.

"Weight Watchers has given me the tools to begin to make the lasting shift that I and so many of us who are struggling with weight have longed for," Winfrey said in a statement.

Oprah Winfrey speaking on her show Soul to Soul (OwnTV/YouTube)

"I believe in the programme so much I decided to invest in the company and partner in its evolution."

Weight Watchers (WTW) concurrently announced an expansion of its brand beyond a pure focus on weight loss to a general emphasis on healthier living.

The Associated Press reported that investors flocked to Weight Watchers shares in the wake of the news, sending the stock up 53 per cent in pre-market trading to $10.36 on Monday morning.

Winfrey bought her shares at $6.79 for a total investment of $43.7m, according to a Securities and Exchange Commission filing.

Weight Watchers International Inc said that as part of a five-year agreement, Winfrey has given the company the right to use her name, image, likeness and endorsement for the company, its programmes, products and services, subject to her approval. She will also make personal appearances on the company's behalf.

"We are expanding our purpose from focusing on weight loss alone to more broadly helping people lead a healthier, happier life," Weight Watchers President and CEO Jim Chambers said in a statement.