NEW YORK -- Oprah Winfrey's loss is Weight Watchers' gain.

The former talk show host, who bought a nearly 10 per cent stake in the weight loss company last year, sent shares soaring Thursday after saying in a new ad that she's lost more than 40 pounds on the plan, all while eating pasta and tacos.

Shedding pounds is Winfrey's financial gain as well as Weight Watchers.

The media mogul spent about $43.2 million in October 2015 for 6.4 million shares. On Thursday, that stake was worth about $77 million, as its shares rose 15 per cent to $12.12 in early trading.

But even Oprah has been unable to outpace enormous changes in the weight loss market. Weight Watchers has been facing increasing competition from free apps and technology that tracks food intake and exercise. So far this year, shares of Weight Watchers International Inc. are down 50 per cent.

Last week, the New York company announced a new plan that would give subscribers an Apple Watch if they pay $99 and $34.95 a month for 12 months.