When the 50 original contestants reconvene in Los Angeles on Wednesday to crown “The Biggest Loser” on the reality TV show, Cheryl Forberg will be there, almost as proud as they are about their svelte new shapes.

She has followed their weight loss longer and more closely than the average TV viewer. As consulting dietitian to the show, the Napa resident has been advising and monitoring the participants since last spring, when this year’s competition began.

Although this is Forberg’s third season with the show, her role is largely invisible to viewers. Only host Caroline Rhea and the two exercise trainers appear regularly on air. Forberg isn’t interested in playing a starring role, but she wishes that the show’s fans saw more of the behind-the-scenes science.

“There’s a credentialed team and medical experts behind the show, and there has been, from day one,” she said.

She and the two consulting doctors have conducted training sessions and worked together to analyze the participants’ calorie needs, advise on diets, monitor their health, review the journals where they log their food intake, and cheer them on when the scale refuses to budge or they fall to temptation.

A registered dietitian and author of “Stop the Clock! Cooking” and two other upcoming anti-aging books, as well as the just-released “The Biggest Loser Complete Calorie Counter,” Forberg is usually more focused on anti-aging research than on dieting. But the two are intertwined, she said. “The foods I recommend to the contestants … are the same things I tell people about in terms of slowing down the aging process.”

She endorses whole grains, and avoids processed foods and artificial sweeteners. “I’m just all about recommending natural foods in their naturally occurring form,” she said. She tells the contestants to be sure that half their plate is vegetables. “We aim for four cups a day of fruit and vegetables, mostly vegetables.”

Viewers of the show see more of the calorie burning exercise component –– also critical to weight loss. But Forberg’s focus has been on educating the participants about healthy eating, a steep learning curve for many of them,

She works with all 50 of the original contestants, not just the 14 who made it to the Ranch the show’s isolated weight loss venue.

This year’s show began with a twist. The producers brought in one contestant from each state, who all thought they were going to be vying for the top prize. When only 14 were selected to participate, Forberg said, “the remaining 36 were devastated. It was horrible.”

They soon found out they were competing after all — but doing it from home. Instead of going to the Ranch they were taken to an L.A. hotel for an intensive week-long boot camp conducted by Forberg and one of the show’s doctors, to start them on their at-home weight loss.

“They learned how to measure and weigh food, and understand portion size, and were introduced to a variety of different whole grains, lean proteins … they learned what their personal calorie goals were, how to exercise, how to grocery shop, how to cook, and then they took all of these skills home to see if they could compete with what was happening at the Ranch.”

The format was a surprisingly successful experiment. With a jump-start from the boot camp and the support of the medical team, many of the at-home contestants have slimmed down at the same rate as those competing on the air.

“At the beginning of the season, we didn’t know that they were going to continue to lose weight. We had no idea they’d lose as much as the people on the Ranch. Everybody was stunned,” Forberg said.

She admits she feels more connection to the people at home, because the majority of her time has been spent checking in with them by telephone and conference call. She is particularly proud of what they have accomplished because, unlike the isolated Ranch contestants, they have stuck to their plan while dealing with jobs, family, and the stresses and temptations of everyday life.

She’s looking forward to seeing them at the finale. “The first day together in Santa Monica at the boot camp, we all ran down to the beach at five in the morning … and some people could barely walk. And now these people are running, they’re training for half-marathons … it’s pretty phenomenal,” she said.

Although filming for the show wrapped up in July, the contestants have continued to exercise and lose weight, and are still checking in with the medical team. But Forberg doesn’t know who the $250,000 grand prize winner will be. That will be determined at the final weigh-in on the live broadcast, with a second significant prize for the at-home contestant who lost the most.

Before returning to school to earn her dietitian degree and credentials, Forberg was on the opening team of Wolfgang Puck’s Postrio, and then worked as a private chef, including cooking for George Lucas. But those glamorous jobs don’t compare to working on the TV show.

“I didn’t expect this, but this is by far the coolest job I’ve ever had,” Forberg said. “To feel like you made one tiny imprint in this transformation, to feel like you could help them in any way. It’s gratifying beyond description.”