Oprah boosts Weight Watchers stocks

Weight Watchers is getting another boost from Oprah Winfrey.

The weight loss company's shares soared on Wednesday as a TV commercial starring Winfrey began to air.

The ad shows past videos of the talk queen working out and referencing her struggle with weight, a frequent topic of her former show.

It ends with Winfrey asking viewers if they're ready to join her. "Let's do this together," she says.

She tweeted the ad to her more than 30 million followers on Tuesday.

Weight Watchers stock has more than tripled since October, when Winfrey bought a 10 per cent stake in the New York company.

Besides the new commercials, Weight Watchers has also made changes to its plans to better fit in with Winfrey's message of living a healthy and happier life, and not just focusing on weight loss.

Shares of Weight Watchers International Inc. jumped $3.68, or 19 per cent, to close Wednesday at $23.05.

Weight Watchers brought in Winfrey at a precarious time for the company. It has been hurt by the popularity of fitness trackers and free food-tracking apps.

Despite recent gains in the stock, the company is still down about 8 per cent from a year ago.

Winfrey is on the new plan and she said in an October appearance on The Ellen DeGeneres Show she lost 6.8 kilos in a few months.

While she slims down, her wallet is getting fatter.

Back in October, Winfrey paid about $US43.2 million ($A59.33 million) for her 10 per cent stake in Weight Watchers. That stake is now worth more than $US148 million.