Weight Watchers may be about shedding those pounds, but it was a stunning gain -- in stock price -- that had the company in the news early this week, and the hoopla was all thanks to talk-show star Oprah Winfrey.

The 61-year-old billionaire took a 10-percent stake in the New York-based firm, buying 6.4 million shares and being awarded options to buy 3.5 million more, USA Today reported. The stock's value, in turn, more than doubled to $13.92 a share, meaning Winfrey herself pocketed some $70 million in just one day, the newspaper calculated.

Winfrey herself is a Weight Watchers member, and she said in a statement that her move was inspired in part by her belief in the program's effectiveness, according to Forbes.

"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," she said. "I believe in the program so much I decided to invest in the company and partner in its evolution."

Weight Watchers CEO Jim Chambers, meanwhile, celebrated the talk show queen's move, saying his company wanted to become less about losing weight and more about leading an overall happy and healthy life. "Through our conversations, it became clear that there is tremendous alignment between Oprah's intention and our mission," Chambers explained.

The media personality's interest in the weight-loss company comes at a critical time for Weight Watchers, which in recent years has struggled with a business model faded amid competition and other diet options, USA Today commented. But investors seem to hope that Winfrey's entry will help reinvigorate the brand.

Nevertheless, research has cast doubt on whether the 52-year-old Weight Watchers plan actually work, and people who were randomly assigned to follow its diet did only slightly better than a comparison group, the newspaper added.

While it has "been one of the chief advocates of calorie counting, that concept may work in the lab, but it's becoming increasingly ineffective in the real world," said David Ludwig, director of the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital. "You can cut back on calories, but that disregards a basic fact that our body fights back as we lose weight."