There are some big surprises in store for viewers when The Biggest Loser's fourth season premieres, including new host Allison Sweeney; the return of former trainer Jillian Michaels; and a new "secret" Black Team of contestants that had failed to be chosen for the traditional Red and Blue Teams.

"Obviously the big surprise twist at the beginning is the return of Jillian as a trainer and a third team.  We've only ever had two teams previously.  With the outcasts as a group, they come back with a chip on their shoulder and I think Jillian equally came back with a chip on her shoulder... and a lot of fireworks follow," The Biggest Loser executive producer Mark Koops told reporters during a conference call last week.

Michaels was replaced by Kim Lyons for the show's third season but will return along with Lyons and original trainer Bob Harper for The Biggest Loser 4 when it premieres with a two-hour special on Tuesday, September 11 at 8PM ET/PT.  Sweeney, who has appeared on the soap Days of Our Lives since she was 16, will be replacing Caroline Rhea as The Biggest Loser's host. 

"We had looked at Alison being the host the first time around when we started the show and she was actually at the time heavily pregnant with her son.  So it hadn't worked out on a timing thing," said Koops.  "As we were moving forward into production [on Season 4], it's a big commitment... Caroline had other interests she wanted to pursue.  I think by mutual consent we decided it was easier for us to look in a different direction.  As soon as we looked in a different direction, we had a very short list of names of one of who we thought it would be the perfect choice.  We were fortunate enough on our to secure the person we wanted and the person the network wanted."

Sweeney described herself as a "fan of reality" and added she's "watched all of the previous seasons" of The Biggest Loser.

"I really didn't think it was appropriate for me to try to emulate Caroline or do what she did or try to do it different," she said.  "I tried not to let that get in my head.  I just am me, and it's a reality show, we're all just us.  So I came into it bringing who I am and my background and relating what these contestants are going through... All I could do was bring me to the table and do the best job I can."

Sweeney presumably didn't have a problem relating to The Biggest Loser 4's 18 contestants, as she said she's "had trouble" with her weight her entire life.

"I think that's a really common theme that most people experience at some point in your life," she said.

However after she "tried everything," Sweeney said she learned nutrition and exercise were important and "the health way is what paid off."  Koops agreed the healthy way of shedding pounds is what The Biggest Loser tries to instill in its contestants.

"We're not about them getting to a particular size or getting to a particular weight," he said.  "We're about them getting healthy, and equally everybody who comes to the show are unhappy about how they look or how they feel and where they've got to in our lives... We're not trying to spout a particular vision of how you should live, apart from be healthy and be happy."

Despite being a fan of the show, Sweeney said hosting The Biggest Loser allowed her to be an "observer."

"Having spent time with them and getting to know them right from Day 1, I was so affected by their stories," she said.  "They really are amazing, brave people before they ever stepped on our scale.  It's just amazing to get to know them and they're such great people... I guess I just didn't realize how involved I would become in all of their lives and how they really became my friends quite quickly... I wanted to see them all succeed... I just never realized how emotionally connected to these people I would quickly become."
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Mostly, Sweeney said it was each contestants' "breakthrough on the scale" that "touches you."

"The Biggest Loser is people who overcome tremendous weight loss and have amazing success on the scale every week.  But it's true whether you have 10 pounds to lose or 100 pounds to loose -- this is a lifestyle change -- and you can make a difference," she said.  "It's just taking them away from everything they're used to and putting them in a new environment where they really have to focus on themselves.  A lot of gets you [in this situation] in the first place is that you don't like to focus on yourself.  You don't like to look in the mirror.  You don't like to deal with what you're going through... You have to want to change.  You have to be self-motivated... It's just coming to terms with who you are."

However she said it's not all about shedding the weight.

"The physical achievements are almost as important to them as the numbers on the scale and the way that they look," said Sweeney.  "They're so proud of their athleticism because they become athletes.  It's truly tremendous what they accomplish and how physically fit they become and the pride that they have in that is what I think carries them in the rest of their lives."

"People ask what The Biggest Loser's diet is," added Koops.  "There's no diet per say.  It's really these people changing their lives... It's a lifestyle change as opposed to a dietary change where you're on one of these fad diets.  The trainers work with each of the contestants individually to find what works for them... That's the way that will really help them achieve something in the game part of it, but that's just a small part of the life lessons that they get to take home with them."

Koops said those life lessons learned by The Biggest Loser participants -- which this season includes the show's oldest contestant ever; a Hurricane Katrina survivor from Louisiana; as well as a set of twins from Long Island, NY -- is completing the promise they've made to live happier and healthier.

"I think the one thing they learn more than anything else is how to finish what they started," he said.  "They've all tried diets before, and they've never learned to finish it.  That's one of the major things they've learned at the campus:  Even if they've lost the challenge, they all want to complete the challenge just to prove to themselves, 'You know I can do it.  I am strong enough.'"

The Biggest Loser 4's two-hour premiere on September 11 will be followed by another two-hour installment on September 18 before airing 90-minute episodes every week beginning Tuesday, September 25 at 8PM ET/PT. On Tuesday, September 4 at 8PM ET/PT, NBC will air a one-hour The Biggest Loser: Where Are They Now? special that will give viewers an opportunity to see the progress -- or lack thereof -- that some of the show's previous contestants have made.

"There's people who have definitely struggled," said Koops, who added the show's "success rate is almost unparalleled."  "We're not afraid as a show to hide from failure.  We're not a magic show.  It's incredibly tough."