Value of Oprah Winfrey's stake in Weight Watchers down over $100 million

Oprah Winfrey's big investment in Weight Watchers has paid off so far, but her Midas touch could be in question given the company's recent struggles.

Winfrey bought a 10 percent stake in Weight Watchers for $43.2 million US in October and joined the company's board. The company's stock more than doubled the day the purchase was announced, and by November, Winfrey's stake was worth nearly $180 million.

Weight Watchers shares have been in a bit of a freefall since, losing more than two-thirds of their value in less than a year. The value of Winfrey's shares is down by more than $116 million.

Weight Watchers CEO James Chambers announced Monday that he was stepping down. Winfrey is part of a committee to find a new leader.

Winfrey, who has had a very public struggle with her weight, discussed the issue in a commercial for Weight Watchers last year and in January announced that she had lost 26 pounds (12 kilos) on the program. In May, she said she didn't think she would ever go off the plan.

Weight Watchers has faced stiff competition as people turn to a number of alternatives, includingpopular step-counting fitness gadgets like Fitbit and free weight-loss apps in an effort to manage their weight.