The Los Angeles Times said Monday that Studdard is the reality show's first celebrity competitor. He beat out runner-up Clay Aiken to win the singing competition's second season in 2003, and later earned a Grammy nomination.
Studdard became a vegetarian in 2006 and dropped 70 pounds, according to People. But gained it back when he divorced his wife, Surata Zuri McCants, in 2012.
"So we used to eat everything," has said of growing up in the south.
"And still to this day I have a problem with sweets, which is something that I hope I can get control over in the near future," he told the Huffington Post last year.
"But everyone has different obstacles that they have to conquer and I'm looking forward to having the opportunity to conquer mine," he added.
According to US Weekly, the 15th season of "Biggest Loser" premieres Tuesday, October 8.