Biggest Loser Alum's Warning To Current Contestants

TMZ broke the story ... nearly all of the remaining contestants on the current season have walked off the show and are threatening to quit -- after learning that producers were considering bringing back previous contestants to compete for the $250,000 grand prize.

The contestants are striking because they feel it's unfair to bring back old contestants -- which would hurt their chances at winning the money.

But 66-year-old John Forger -- who competed on Season 12 -- tells TMZ, "It's not about [money]. What it's really about, for most of us, is the change in our lifestyle, and being able to get rid of obesity."

John adds, "For most of us, it's about health. Would I walk off the show for the money? ABSOLUTELY NOT."