Oprah Winfrey announced Monday that she’s taken a 10 percent stake in Weight Watchers and is joining the company’s board. The media mogul said the company has helped her to lose weight, and now she wants to “partner in its evolution.”

Weight Watchers will no doubt get a boost from Winfrey acting as a brand ambassador who will chronicle her own experiences with the company’s weight loss program. But the $65 billion weight loss market still faces many challenges, among them, people who prefer to diet on their own instead of paying a company for help.