Billionaire media mogul Oprah Winfrey has acquired a 10% stake in Weight Watchers International, sending the dieting company’s stock soaring Monday after a prolonged slump.

Winfrey, who is also getting options to acquire an additional 5% stake, is joining the Weight Watchers board after a positive personal experience with the company’s weight-loss program.

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

Investors flocked to Weight Watchers shares in the wake of the news, sending the stock up 86% to $12.60 at 10:25 a.m. Monday.

Winfrey bought her shares at $6.79 for a total investment of $43.2 million, according to a Securities and Exchange Commission filing.

The burgeoning share price may reflect the power of Winfrey’s brand in driving interest in health-related products and programs as much as it reflects her bet on the company’s business model. The company’s stock had lost 72% of its value this year before her investment was publicized.

“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. “I believe in the program so much I decided to invest in the company and partner in its evolution.”

In addition to her role as a board member, Winfrey, who has long shown an interest in health issues and dieting programs, will serve as an adviser to the company.

“Through our conversations, it became clear that there is tremendous alignment between Oprah’s intention and our mission,” Weight Watchers CEO Jim Chambers said in a statement. We believe that her remarkable ability to connect and inspire people to realize their full potential is uniquely complementary to our powerful community, extraordinary coaches and proven approach.”

Weight Watchers has been slumping in recent years as dieting is going digital. Fewer people are interested in Weight Watchers’ famous group meetings, where experts and colleagues share dieting tips.

An increasing number of dieters are counting calories with smartphone applications or have shifted their emphasis from caloric intake to healthy eating.

Weight Watchers’ total revenue fell 19% from $1.84 billion in 2011 to $1.48 billion in 2014. That included declines in meeting revenue, product sales and licensing fees.

The company has responded by investing in digital consultation with a new service called Personal Coaching, which offers personalized health advice through email, text-messaging and phone calls. It has also invested in online technology such as personalized accounts that sync with activity-tracking devices such as FitBit.

About 800,000 members attended Weight Watchers meetings in 2014, and 1.5 million people subscribed to the company’s online products.

Winfrey’s deal includes the option to buy an additional 5% of the company for $6.97 per share.

She can’t sell any Weight Watchers stock for the first two years, according to deal terms filed with the SEC. She can sell up to 15% in the third year of her investment, up to 30% in the fourth year and up to 60% in the fifth year.

In five years she would have the right to sell all of her shares.

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.