THE BIGGEST LOSER. 8 p.m., Channel 10.

CALABASAS, Calif. - For all of the things that Mark Koops, an executive producer on NBC's hit weight-loss competition series "The Biggest Loser," has reason to worry about - ratings, scheduling, shooting logistics - coming up with compelling and legitimate storylines strong enough to fill a weekly two-hour episode isn't one of them. What Koops has taken away from "The Biggest Loser," in which a group of dangerously overweight people work out with fitness experts, learn about diet and exercise, and compete for a $250,000 prize, is that deciding what to follow is the difficult part.

Especially early in the season, when tears flow freely and heartbreaking confessions of excess and self-loathing never seem to stop. "The trainers believe that weight gain is a manifestation of other problems," Koops said. "It's not just the love of food, it's born of something else. We know that with moderately to morbidly obese people going through massive life transformations we're going to have almost too much story."

This is not to say that "The Biggest Loser," which begins its fifth season tomorrow, doesn't also traffic heavily in forced catchphrases, obvious marketing tie-ins and wacky challenges, like an endurance contest involving a mechanical never-ending jump-rope. It's just that nothing, not the abrupt close-ups of Jennie-O Ground Turkey labels or stagy advice sessions in which trainers "educate" the contestants on the appetite-dulling charms of Wrigley's Extra Supermint sugar-free gum, can dampen what is genuinely moving about the show: seeing confident, happy men and women slowly emerge from their formerly shame-filled, lumpy-bodied and droopy-shouldered selves.

For Nicki Britton, who writes a tartly funny blog about "The Biggest Loser" for the Houston Chronicle, every week is a new chance to be touched by the sight of contestants clad only in unflattering exercise clothes at the "Biggest Loser" weigh-in, hoping their sweat and toil that week result in some pound-shedding. "The amount of courage that it takes for these ordinary people to stand on a scale in front of America practically naked, it just astounds me," Britton said in a phone interview, adding that her own 49-pound weight loss through Weight Watchers is one reason she sees glimmers of herself in the series.

Nonetheless "The Biggest Loser," which debuted in October 2004 and now exists in dozens of international versions, is still a reality game show, and therefore has a vested interested in plot "twists" to augment all the natural human drama.

This season's spin? Contestants come packaged in twos - husbands and wives, mothers and sons, best friends - and 10 sets of two will weigh in, bunk and train in tandem. Koops said he and the executive producers, J.D. Roth and Dave Broome, hatched the pairs idea during the early stages of last season. That was when a Long Island, N.Y., police officer, Jim Germanakos, was sent home, but his identical twin, a salesman named Bill, was not. The elimination fell on the night before their birthday, which meant, among other things, that for the first time in their lives the Germanakos brothers wouldn't be blowing out candles together.

Suddenly the dramatic possibilities of focusing on contestants with a shared history seemed glaringly apparent. (Bill Germanakos ended up taking home the Season 4 grand prize, while his brother won the weigh-in for a parallel competition in which contestants who had been eliminated continue to lose weight on their own.) While the friction-creating dynamic of duos has already been milked on "The Amazing Race," Koops said that on a series that deals with binge-eating out-of-shape Americans, the term "support system" becomes a double-edged sword.

"Normally there's no one else to fight for control with," he said of the previous emphasis on individual struggles. "It's been very interesting for the trainers: How do you train someone when their enabler is there? How do you break some of those bad habits? I think we did anticipate that to a degree, but saw it play out fivefold." *