From People, where you can read the full story:

The “Velvet Teddy Bear,” who won season 2 of the Fox singing competition in 2003, will compete on the NBC weight loss show as he attempts to battle his obesity – a task he has attempted previously with limited success.

“I was losing weight, but I was exhausted. It was making me sick,” the 35-year-old told PEOPLE in 2006 after attempting an intense workout regimen on about 1,200 calories a day with trainer Gunnar Peterson. “I’m a big man. There was no way to do those workouts on that amount of food, so everything was contradicting itself.”

Studdard quit that weight-loss plan after losing just 12 lbs., but eventually found vegetarianism which – along with exercise – resulted in his losing more than 70 of his 455 lbs. in 2006.

“Every week we would start by writing out a meal plan and calories,” Studdard said about his then-new diet. “The people at the vegetarian store in Birmingham are like, ‘What’s he doing in here?'”