The company says the new name reflects its development from focusing on weight loss to overall health and wellness.
But the chief executive was unable to explain what the letters WW stood for.
Mindy Grossman said they did not stand for Weight Watchers or “Wellness that Works”, a phrase that the company has trademarked, but were simply “a mark”.
Ms Grossman, who took the helm just over a year ago, told the BBC the letters represented “the transition from the name to the mark that stands for more”.
“That mark represents our heritage and history and what we are going forward,” she said.
She said the firm had been shifting from a focus on just weight loss to its broader remit looking at “wellness” over the past two years.
“This is just a next step, a point of validation. Business brands have to stay relevant,” she said.
Oprah Winfrey bought a 10% stake in Weight Watchers in 2015
US media personality Oprah Winfrey – who bought a stake in the company in 2015 and works as an ambassador for Weight Watchers – said she had always thought that the company’s role in people’s lives “goes far beyond a number on the scale”.
The new name comes amid a growing backlash against the word “weight” with social media campaigns such as the #iweigh hashtag gaining popularity.
The campaign, started by “The Good Place” star Jameela Jamil, encourages others to look beyond their weight, and instead to count other “measurements” in their life such as your “three best friends” or your “one loving sister.” The iweigh Instagram account now has 153,000 followers.
Other successful campaigns have encouraged a focus on fitness, rather than appearance.
Sport England’s campaign called This Girl Can aim to encourage more women to take up exercise and featured women of all shapes and sizes taking part in a variety of sports.
Social media hashtags such as #StrongNotSkinny and #FitNotThin hashtags have also grown in popularity.
Weight Watchers’ rebranding includes updating its so-called Fit points system to encourage subscribers to choose activities which have the biggest impact on health, and a new focus on “healthy habits” in its app for those “who want to build healthy habits without focusing on weight loss”.
The rebrand is aimed at broadening its appeal to attract more potential users, but also to encourage subscribers to stay with them in the long run.
Its latest results show sales rose nearly 18% in the three months to the end of June, with subscribers up by one million from a year earlier to 4.5 million.
At the time, Ms Grossman said it was planning to present “our brand in a new, modernized and culturally-relevant way.”