Players will be able to "compete in 4, 8 or 12 week programs against former contestants from the television show," and the game even allows players to "receive credit for any progress made while not playing the video game, such as going for a walk or a bike ride." The choice of the honor system here leaves the door open for all manner of dubious exercising. Can you "beat" the game without shedding a pound? Now there's a challenge.
The two different versions will interact with each other, allowing DS players to take their trainers from the Wii game with them to the grocery store to count calories and choose sensible meals. The Wii version of the game also supports the Balance Board, which is pretty much a requirement of any fitness game on the Wii, and will allow players to perform weigh-ins at regular intervals, and choose from a variety of different exercise options.
You can see if you're The Biggest Loser when the game releases this fall.