Dr. Rob Huizenga, the medical consultant to “The Biggest Loser” and an associate clinical professor of medicine at U.C.L.A., said that the program was 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,” he said.

In interviews, the show’s trainers and producers acknowledge that unsafe practices can occur.

“If we had it to do over, we wouldn’t do it,” Dr. Huizenga said of the recent one-mile race that resulted in hospitalizations. “It was an unexpected complication and we’re going to do better,” he said, adding that “that challenge has changed a lot of the way we do things,” including more closely monitoring contestants’ body temperatures during exercise.

JD Roth, an executive producer of the series who created its current format, said that while the show was extreme, “it needs to be extreme in my opinion.”

“For some of these people this is their last chance,” he said. “And in a country right now that is wrestling with health care issues and the billions of dollars that are spent on obesity issues per year, in a way what a public service to have a show that inspires people to be healthier.”

Image A trainer on the television show “The Biggest Loser” said the experience of Ryan C. Benson, who, pictured before and after, used dangerous weight loss techniques to win the contest in 2005, represents the dark side of the program. Credit... Trae Patton/NBC Universal

Some contestants have claimed that dangerous weight loss techniques were common among contestants. Kai Hibbard, who lost 118 pounds and finished as the runner-up in Season 3, has written on her MySpace blog and elsewhere that she and other contestants would drink as little water as possible in the 24 hours before a weigh-in. When the cameras were off, she said, contestants would work out in as much clothing as possible.

Ms. Hibbard, who weighed 144 pounds at the show’s finale, wrote that she added 31 pounds in two weeks, most of it simply by drinking water. That experience is not isolated. Including Mr. Benson, the winners of the first four seasons of the show each have added at least 20 percent to their weight at the end of the show.