Oprah just made a big bet on Weight Watchers

Oprah Winfrey just made a big bet on Weight Watchers.

In a press release on Monday, the weight-loss assistance company said she joined its board and purchased newly issued stock representing a 10% stake of shares outstanding. She also bought options to acquire an additional 5% of fully diluted shares.

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According to the release, Oprah became an adviser, as well as a regular member of the program who will "candidly share her experiences and perspective along the way".

See photos of Oprah from her early days:

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

Weight Watchers shares surged by as much as 38% in premarket trading.

The stock is down 72% year-to-date and over the past year.

The company has struggled to lift sales and increase its membership. A Duke University study found earlier this year that the company faced strong competition from rivals. And, Credit Suisse analysts said free weight-loss apps were a better deal for some consumers than Weight Watchers membership.

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