The Biggest Loser (season 1) is the first season of the NBC reality television series entitled The Biggest Loser, which premiered on October 19, 2004. The show features overweight contestants competing to lose the largest percentage of their body weight and receive the title of 'Biggest Loser,' along with a $250,000 grand prize. The first season featured twelve contestants divided into two teams of six players. The teams were each led by a personal trainer, Bob Harper with the Blue Team and Jillian Michaels with the Red Team. The first season was hosted by Caroline Rhea.

The Biggest Loser (season 2) is the second season of the NBC competitive reality television series entitled The Biggest Loser. The second season premiered on September 13, 2005, and like season one features overweight contestants who compete by trying to lose the most weight. The show is hosted by comedian Caroline Rhea, with Bob Harper and Jillian Michaels joining as the two personal trainers. The contestants were divided into two teams: men in red and women in blue, with each team assigned to their own personal trainer of the opposite sex. Each week, the team which had the lowest percentage of total weight-loss was required to vote out one member of their own team. The show concluded November 29, 2005, when Matt was declared "The Biggest Loser", winning $250,000. Seth was awarded $50,000 for his second place finish, and Suzy was awarded $25,000 for third. Of the non-finalists, Pete had lost the highest percentage of weight and received the $100,000 prize.

The Biggest Loser (season 3) is the third season of the NBC reality television series entitled The Biggest Loser. The third season premiered on September 20, 2006 with fifty overweight contestants, each competing to lose the most weight. However, first, the group would be narrowed down to 14 after the trainers each selected seven competitors for their teams. The show was hosted by comedian Caroline Rhea. Bob Harper and Kim Lyons were the two personal trainers, with Bob leading the blue team and Kim leading the red team. The show's opening theme song was 'Proud' by Heather Small. The opening credits showed each contestant in turn, and displayed his or her starting weights. Each week of the show, one contestant was voted off by the others. Midway through the show, the two at-home participants who lost the most weight came back on the ranch. Ultimately, a set of four finalists were determined before the show began airing. On the final episode, aired live, those finalists reunited for a weigh-in to determine the winner. At the finale, it was revealed that Heather would not weigh in to compete for the prize money because she was 5 months pregnant. Of the three other finalists, Erik had the largest percentage of weight loss, with 214 lbs, which was 52.58% of his starting body weight. He received $250,000 for this feat. Additionally, Poppi from New Jersey, who lost the most of the 36 who didn't make it to the regular season won $50,000, and the individual who lost the most out of the remaining 14 who were on the show, but not finalists, won $100,000. This player was Brian from California, who lost 50.65% of his weight.

The Biggest Loser (season 4) is the fourth season of the NBC reality television series entitled The Biggest Loser. The fourth season premiered on September 11, 2007 with 18 overweight contestants in a weight loss competition for an ultimate prize of $250,000. The Biggest Loser campus was located at California State University Channel Islands in Camarillo, California. The season four contestants were divided into 3 teams: the Red team, led by trainer Kim Lyons; the Blue team, led by trainer Bob Harper; and the Black team, led by trainer Jillian Michaels. The teams were formed on the first episode, with the Red and Blue teams being selected by the two players who had won a foot race across the desert. The Black team was formed with the 6 remaining contestants who were not selected for the Red and Blue teams. While the Red and Blue teams returned to the Biggest Loser campus, the Black team was left behind, believing that they had been eliminated already. Instead, they remained in the desert and trained in secret with their trainer, Jillian, until they arrived on campus for the weigh-in at the end of week 2.

The Biggest Loser: Couples is the fifth season of the NBC reality television series The Biggest Loser. The fifth season premiered on January 1, 2008 with ten overweight couples competing for a cash prize of $250,000. This season featured Alison Sweeney as the host, with trainers Bob Harper and Jillian Michaels; all three returning from season four. Although the contestants came in as teams of two, the grand prize was eventually awarded to an individual. In the end Ali Vincent won, making her the first female winner in the history of the United States Biggest Loser series.

The Biggest Loser: Families is the sixth season of the NBC reality television series The Biggest Loser. The sixth season premiered on September 16, 2008, featuring Alison Sweeney as the host and Bob Harper and Jillian Michaels as the contestants' trainers. The cast was revealed on August 29, 2008. Eight duos began the challenge, adding up to a total of 16 contestants. From Week 1 to Week 5, the Green, Red, Orange & Brown Teams trained with Bob, while the Purple, Gray, Yellow & Pink Teams trained with Jillian. In Week 5, these "Family Teams" were disbanded and the contestants were split into the Blue Team and the Black Team. In week 8, the teams were split again and the competition went into individuals. Amy Cremen was originally under Jillian's training, but in week 5, was placed in and eliminated under Bob's training. Phillip Parham started the competition under Bob's training but was eliminated under Jillian's training. Michelle Aguilar was named the Biggest Loser on December 16, 2008, after losing 110 pounds. She won $250,000. Heba was named the Biggest Loser of the eliminated contestants, and won $100,000. However, if Heba were not eliminated during the finale by America's vote she would've become the Biggest Loser.

The Biggest Loser: Couples 2 is the seventh season of the NBC reality television series The Biggest Loser. The season premiered on January 6, 2009, with eleven overweight couples competing for a cash prize of $250,000. Alison Sweeney is featured as the host, with trainers Bob Harper and Jillian Michaels. Helen Phillips won the competition with a total weight loss percentage of 54.47%.

The Biggest Loser: Second Chances is the eighth season of the NBC reality television series The Biggest Loser. The contestants competed to win a $250,000 prize, which was awarded to Danny Cahill, the contestant with the highest percentage of weight lost. This season premiered on NBC on Tuesday, September 15, 2009. The season's theme meant that each of the candidates had met with heartbreak and tragedy during their lifetime. Among notable stories, Shay Sorrells grew up in foster care while her mother unsuccessfully struggled with heroin addiction, while Abby Rike lost her husband and children in a head-on collision caused by a speeding driver. Amanda Arlauskas became a contestant after winning a public vote against Erinn Egbert held during the Season 7 live finale. Contestant Daniel Wright was a contestant in Season 7, and has returned to "finish what [he] started". Another change to the format this year is that the two trainers will work with all contestants rather than splitting the contestants into two camps and creating an imagined competition between the two trainers. In the fifth week, when teams are changed to blue and black, Jillian leads black while Bob leads blue.

The Biggest Loser: Couples 3 is the ninth season of the NBC reality television series The Biggest Loser. The contestants competed to win a $250,000 prize, which was awarded to Michael Ventrella, the finalist with the highest percentage of weight lost. It first aired January 5, 2010. After six episodes, The Biggest Loser went on hiatus and returned after the 2010 Winter Olympics on March 2, 2010. The live finale aired on May 25, 2010. The season premiered on NBC on January 5, 2010 and tallied its best premiere rating ever, powering NBC to the adults 18-49 ratings win for that night. Biggest Loser: Couples was up 2% from its January, 2009 premiere to a 4.6 adults 18-49 rating. It was the top adults 18-49 rated Biggest Loser premiere and tied the second best rating for a non-finale. It scored a total 11.68 million viewers. This was also the last season to be filmed in 480i, due to the fall 2010 season moving to high definition.

The Biggest Loser: Pay It Forward is the tenth season of the NBC reality television series entitled The Biggest Loser. The contestants competed to win a $250,000 prize, which was awarded to Patrick House, the contestant with the highest percentage of weight lost. It premiered on September 21, 2010 as the first season to be filmed in high definition, and concluded on December 14, 2010.

The Biggest Loser: Couples 4 is the eleventh season of the NBC reality television series entitled The Biggest Loser. The contestants competed to win a $250,000 prize, which was awarded to Olivia Ward, the contestant with the highest percentage of weight loss. It premiered on January 4, 2011. Along with existing trainers Bob Harper and Jillian Michaels, two new trainers will be featured who were revealed in Week 3. One of the featured contestants is Rulon Gardner, a former gold medalist at the 2000 Summer Olympics. It was the longest season in Biggest Loser history at 20 weeks long. This season is the second, after Pay It Forward, to be filmed in high definition. This season marks the first time in USA Biggest Loser history that a contestant left the show by choice. As well, for the first time in The Biggest Loser history, a couple has made the finale together. And, for the first time in The Biggest Loser history, all 3 finalists are women.

The Biggest Loser: Battle of the Ages is the twelfth season of the NBC reality television series entitled The Biggest Loser. The contestants competed to win a $250,000 prize, which was awarded to John Rhode, the contestant with the highest percentage of weight lost. It premiered on September 20, 2011. Along with existing trainer Bob Harper, two new trainers joined this season. The 15 contestants this season were divided into three groups of five by their ages: those who are 30 and under were initially trained by Quince, those who are between 31–49 were initially trained by Harper, and those who are 50 and over were initially trained by Kournikova. This season marked the first time since season 5 that America did not have to vote on who would become a finalist. For the first time ever in Biggest Loser history, all 3 finalists were men.

The Biggest Loser: No Excuses is the thirteenth season of the NBC reality television series entitled The Biggest Loser. The contestants competed to win a $250,000 prize, which was awarded to Jeremy Britt, the contestant with the highest percentage of weight lost. It premiered on January 3, 2012. Alongside veteran trainer Bob Harper, Dolvett Quince returned for his second season. The contestants come to the ranch in pairs, but are split up with one person training with Bob and one with Dolvett and the teams competing against each other and their loved ones in challenges.

The Biggest Loser: Challenge America is the fourteenth season of the NBC reality television series entitled The Biggest Loser. The contestants will compete to win a $250,000 prize, which will be awarded to the contestant with the highest percentage of weight lost. It premiered on January 6, 2013. Alongside veteran trainer Bob Harper and returning trainer Dolvett Quince, Jillian Michaels returned for the first time since Season 11. The contestants have been split into 3 teams, the white team trained by Jillian, the blue team by Bob, and the Red team by Dolvett. In addition, three younger contestants are participating, but not subject to elimination. This was the first time since season 12 that America decided who made it to the live finale.