US film and TV star Oprah Winfrey is buying a 10 percent stake in Weight Watchers International and joining the board of the struggling weight-loss company, sending its shares soaring 86 percent.

Winfrey, one of the world's richest celebrities, who has fought a long battle in controlling her weight, said she was forming a partnership with Weight Watchers to inspire people worldwide to lead a healthier life.

"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," Winfrey said in a statement.

"I believe in the program so much I decided to invest in the company and partner in its evolution."

Winfrey said she will join the Weight Watchers program and share her experiences with the public. The weight management program includes weekly meetings for group support and information on developing healthy eating and physical activity patterns.

Winfrey, 61, has built a financial empire through savvy branding of her name and image. The television mogul, author and actress is also known for spotting talent -- books chosen for her Oprah's Book Club regularly end up on best-seller lists.

With a net work of $3 billion, according to Forbes, Winfrey's endorsement of Weight Watchers could lift the flagging performance of the company, which has suffered as consumers turn to free online programs and wearable fitness trackers to manage their weight.

Weight Watchers shares gained 86.2 percent to $12.69 in opening trade.