They were picked out of thousands of people eager to lose masses amounts of weight on television, but now some former contestants of The Biggest Loser are sharing stories of unsafe weight-loss practices on the hit NBC show.

In an article in The New York Times, Season 1 winner Ryan Benson—who lost 122 pounds, but is now back to 300 plus—says he has been shunned by the show after admitting that he helped his weight loss by fasting and dehydrating himself to the point of urinating blood. Kai Hibbard, the runner-up in Season 3, admits to similar practices, saying that some contestants would drink and eat as little as possible before a weigh-in and work out in as much clothing as possible when the cameras weren’t rolling.

Each week on The Biggest Loser campus, contestants drop a substantial amount of weight, often in the double digits for several weeks in a row. Medical professionals consider losing more than two pounds a week unsafe, because rapid weight loss can weaken the heart muscle. But producer J.D. Roth tells the Times that extreme measures are required when contestants enter the competition. “For some of these people this is their last chance,” he said. The Biggest Loser’s medical consultant, Dr. Rob Huizenga, also says the program is safe. “This is not only a major amount of weight loss, it is a totally different kind of weight loss compared with surgery or starvation diets."

Trainer Jillian Michaels calls the issue of contestants taking extreme measures to win a weigh-in the “dark side of the show. Contestants can get a little too crazy and they can get too thin,” she told the Times. She said contestants are medically checked and disqualified if they are dehydrated or are found to be taking drugs or diuretics. “That is the worst part of the show,” she said. “It’s just part of the nature of reality TV.”