Transcript for New Study Reveals Why 'Biggest Loser' Winners Often Regain Weight

Welcome to the show. Thank you, Amy. We begin with that "Biggest loser" bombshell. Many of the contestants gained the weight back and all part of a diet study reported in "The New York times." The winner will join us in a moment. Danny Kaye hill and Dr. Ashton is here as well but first linsey Davis is here with the story. Good morning, linsey. Reporter: Even bigger than the big reveries we have come to expect on extreme weight loss shows is this new research that take as I look what happens after the after pictures and how biology may play a bigger role than will power when it comes to keeping the weight off. We are inundated with weight loss before and after pictures and reality TV shows where overweight contestants end their seasons half the man or woman they used to be but now a new study says if you regain weight after losing it your body may be to blame. In a recent study a group of scientists followed 14 of the 16 contestants from one season of "The biggest loser," monitoring them for the six years after the show. They found that all but one of them gain ed the weight back. While the contestants all had Normal me tab limps for their size at the start of filming years after it was over their me tab limps continued to slow down, a mechanism the body uses to return to its original weight. Further compounding the problem, researchers found the contestants had plumbing levels of leptin, a hormone thought to control hunger which left them constantly feeling hungry. After you lose weight, your body's metabolic rate will slow down, the number of calories your body requires is going to decrease and that's going to make it difficult for you to keep the weight off. I had my life back. Reporter: Difficult for people like Danny Kaye hill. 430 pounds before the show, 191 pounds after. But gained nearly 100 pounds back after he returned to work. And Dina murcato, 248 before the show down to 173 1/2 pound, now back to almost 206 pounds. The study found her metabolic rate now burns almost 438 fewer calories per day than would be expected for a woman her size. Had I known what I know today I probably wouldn't do the show. I didn't want people to know I was on "The biggest loser" because I don't look like that. Reporter: But the creator of "The biggest loser" defends his show. When the people leave our show, they are better off than being 400 pounds. I do think the study could have done things a little bit differently. I would have also liked them to take 14 people who kept the weight off. We need to use both to come up with the best way to be healthy because we all know we're still trying to figure it out. Reporter: In response to the study producers of "The biggest loser" released this statement saying "The lead medical doctor on the show has been plead aware of this most recent study and is in the process of evaluating its findings" for those dieters who plane themselves this may lift the biggest weight of all off their shoulder. Over to robin. Joining us "The biggest loser" winner Danny Kaye hill and ABC news medical contributor Dr. Jennifer Ashton. Danny, so good to meet you. We heard in linsey's piece after you won and you said that you got your life back and you felt like a million bucks. What happened after that? You know, I did feel like a million bucks. After that, for a couple of years I kept the weight off completely. But I was -- I wondered why others were gaining it back but what I didn't realize I was working out two hours a day riding my bike all over town to go where I was going. I was exercising three or four times as much as the Normal person and once that stopped, the weight started creeping back on. When you hear this study, how do you process that information? Well, number one it's great because a lot of the shame that is on our shoulders, I mean, when you gain weight back even when you're in school it's shameful. When you're in front of America, then it's even -- it's ten types as shameful and so many people that I've talked to including myself when we found this out we were like, all right, some of it is not our fault. We can't be victim to it but it is our responsibility but some of it has to do with this science. And sitting here with you is somebody -- you were just recently, Jen, board certified in obesity medicine. Uh-huh. It's not just about contestants like Danny on "The biggest loser." This affects everyone trying to lose weight. Especially in the obesity medicine world so this is something that has been known in the medical and scientific community for almost 20 years, robin and it's a concept called metabolic adaptation or some call it the defense of fatness. Let me show you. If you take two individual, both weighing 200 pounds one is at their ideal weight, one has lost 20 pounds to get to 200 which is an incredible success in the weight loss world, the person who's lost weight at 200 pounds has a slower metabolism and burn fewer calories and are hungrier and less full than a person at the same weight. To be clear there are some successes but the majority of people who have lost significant weight at the two-year mark fail to keep it off. They regain that weight and this does not mean that they are failures as Danny said. This is medical and scientific reality. How do you hear this information, Jen, and not get discouraged. I think by turing it into a positive because we know that there are multiple factors that goes into the conditions of overweight and obesity. This is a complex problem. The gold standard now in the world of obesity medicine is kind of a pyramid. If you look at the bottom, no question, behavioral modification, diet, exercise, then you go to fda approved weight loss medications because we need to treat this as a chronic illness and then at the top of that is bariatric surgery and it's about using all these tools in your arsenal and incorporating the psychological and emotional factors, as well. Very important you saw in there still about exercise. That's the foundation. That is something you're continuing to do, Danny. Yes, and not as much as I used to and that's part of why I've gained -- I gained most of my weight back the last year and a half when I got a job because I sit at a desk now and had to retrain myself and have a whole new schedule. You know, but the Numbers don't define me. You know, and I'm not going to be victim to it and we don't have to be. We can -- I mean, I know that I'll do what David did when he tackled goliath. I know there's a bigger -- there's a bigger god out there that wants me to be well and I am going to do everything I can but I can't do it all. That's the whole trick. If I keep trying to do it all -- That's not going to work. I love how you talk about your family and know why you want to keep your weight down because of your family. And I always say, you got to find your why and have a reason why. Well, this study to me is a stepping stone into where we're going to direct even more studies and we're going to find a lot of answers so this puts a whole new purpose to my journey. See, I love -- you both have found a positive because people waking up and hearing about this are like, oh, throwing their hands up. Always strive for good health. So night to meet you and, Jen, up take questions on Twitter because I know you will have a lot of questions. Tweetary @drjashton.

This transcript has been automatically generated and may not be 100% accurate.