Oprah Winfrey has bought a stake in Weight Watchers.

The 61-year-old chat show host, who has battled with the bulge over the years, has snapped up a 10 per cent stake in the slimming company in a bid to broaden the dieting firm and turn it into a varied health and fitness brand.

She said: ''I believe in the program so much I decided to invest in the company and partner in its evolution.''

According to MarketWatch, the brunette beauty will team up with the brand for at least five years while she endorses its products, spreads the word about its programme, becomes an advisor and attends meetings as a board member.

She added: ''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.''

Since she's jumped on board the company, the shares have almost doubled, giving her a paper profit of $45.6 million.

She will also receive the option to buy another five per cent of the company in due course but she has been blocked from selling any shares for at least two years to show that she has faith in the long-term prospects for the company.

Jim Chambers, Weight Watchers chief executive, said: ''Through our conversations, it became clear that there is a tremendous alignment between Oprah's intention and our mission. We believe that her remarkable ability to connect and inspire people to realise their full potential is uniquely complementary to our powerful community, extraordinary coaches and proven approach.''