'The Biggest Loser' debuted 20 years ago. Here's what the show got right — and wrong — about weight loss.

On The Biggest Loser, contestants were put on calorie-restricting meal plans, made to complete hours-long daily workouts that led to vomiting and dehydration and participate in shirtless weekly weigh-ins to keep track of who was dropping the most pounds — which meant advancing in, and ultimately winning, the show’s $250,000 cash prize.

The reality competition was a huge success. It aired on NBC for 17 seasons and still reached millions of viewers at its lowest ratings when it ended in 2016. Now, 20 years after its debut on Oct. 19, 2004, the series has been criticized for contributing to a culture of fat phobia and for demonstrating disordered behaviors when it comes to both food and exercise. Many of its contestants have continued to struggle with weight management after going through the experience, some even with mental health, while coming to terms with the drastic changes that occurred to their bodies during their 30 weeks on the show.

Research — and hindsight — has allowed for a more nuanced understanding of weight, how it pertains to health and what leads to healthy weight loss. Here's what the show got right — and wrong — about weight loss.

'The Biggest Loser' is not a long-term solution

While the contestants deemed to be the most successful celebrated significant weight losses by the end of their seasons, most have experienced some regain. That’s because their weight loss processes simply weren’t sustainable or applicable to life outside of the show, according to Dr. Chika V. Anekwe, obesity medicine physician at Massachusetts General Hospital Weight Center and an instructor in medicine at Harvard Medical School.

“The biggest difference between The Biggest Loser and long-term weight loss strategies is simply that long-term strategies are appropriate for weight loss and weight maintenance since obesity is a chronic disease. So for the impacts to last, the behaviors must continue,” Anekwe tells Yahoo Life. “This was the fatal flaw of the show’s premise — that these short-term behavior effects were weaponized by the trainers and fitness coaches on that show to cause drastic weight loss, but the behaviors were never meant to be continued long term so it was a set-up for weight regain.”

Ashley Johnston Palu, runner-up on the show’s ninth season in 2010, tells Yahoo Life that’s been her experience. “I know undercounting our calories and undereating our calories and working out as much as we did does not set up anybody for success for the long term,” she says. Palu lost 183 pounds during her time on the show and then regained some in the years following. She’s since adjusted her behaviors and even started using a GLP-1 to lose 100 pounds again — a journey she shares on TikTok.

The show portrayed weight gain and weight loss as a matter of willpower, which experts now clearly state is not the case.

How metabolism works

Dr. Kevin Hall, an expert on metabolism at the National Institute of Diabetes and Digestive and Kidney Diseases, which is part of the National Institutes of Health, followed 14 of the 16 Season 8 competitors from their starting point on the show and again six years after.

Hall found that the stronger the weight loss intervention, the more weight that a person would lose and the slower their metabolism would become. “So in some sense, the slowing of metabolism is a marker that you're actually really intervening in some way, you're really making a change,” he says. And while his findings have at times been misinterpreted to show that The Biggest Loser had detrimental effects on a contestant’s metabolism and made weight loss or maintenance more difficult in the long run, Hall says that’s not true.

“The people who had the greatest slowing of metabolism were the ones who lost the most weight in the competition,” he says. “It didn't predict who would regain the most weight. And in fact, six years later, the ones who maintained the slowest metabolism for their predicted values based on their body composition change were also the ones who were the most successful at maintaining the weight loss.”

It also highlights a biological difference between different types of bodies, as somebody who always weighed 180 pounds would have a higher metabolism and be able to consume more calories while maintaining that weight than a person who lost weight to become 180 pounds.

He predicts that some of this information might be telling of the impact of modern weight loss medications. More applicable to the general population, however, is the indication that the mechanisms of weight loss and longer-term weight maintenance are different, which he also found in the study.

Exercise isn’t the primary mechanism for weight loss

Palu remembers exercising eight hours a day while on the show. While physical activity is important, it plays a larger role in the long term. The “active weight loss” phase is all about restrictive caloric intake.

When it came to maintaining that loss, Hall witnessed a shift. “It's the people who became the most physically active who had the best success over time, keeping the weight off. Whereas differences in how many calories people continue to kind of cut from their diet seem to have less of an effect.”

Anekwe says that broader studies on weight regulation have shown a similar pattern. One even emphasized the need to find innovative ways to motivate people to exercise, which Palu says The Biggest Loser ultimately did not do. “It kind of made me fear working out,” she says, referring to the extreme exercises that would make her throw up. “There's so many ways to move your body that don't include puking. … Just find some way to move your body that makes you feel good.”

Overexercising should also be avoided to deter compulsive behavior, injuries or other health issues, warns Hall.

Calorie counting is helpful … to an extent

Contestants were provided some nutritional education and an outline of macronutrient needs, Cheryl Forberg, a registered dietitian and former nutritionist on the show, previously told Today’s Dietitian. Palu, however, recalls an emphasis on calorie counting.

“I did become a little obsessed with counting calories. I wouldn't even eat a stick of gum without logging it,” she says. “I really wish I had eaten more calories while I was on the show. I only ate 800 a day, and now I would never do that low or advise anybody to ever do that low. That was impossible to maintain when I got home. So that would be one thing that I would change.”

Palu says that the show’s medical experts provided her with that daily calorie goal, although she takes accountability for adhering to the restriction as she did. Kai Hibbard, a season 3 contestant who has spoken out against the show, tells Yahoo Life that the guidance around food only had a detrimental effect on her.

“I perfected disordered eating habits,” she says, noting that she’s since gained perspective about the pervasiveness of diet culture at the time and how it impacted others in her generation as well. “I’ve seen so many women who are my age or older that are suffering from health issues brought on by the nutritional deficiencies that came from restricting for so many years when we were young to maintain an aesthetic that we were told was necessary to not only be healthy but to be treated with human dignity.”

Hall says the impact of quality of food rather than quantity is an active area of research. “The quality of the food dictates how many calories the body wants to consume,” he says. “And so calories are still important, but when you focus on the quality of the food and certain aspects of nutrition, then the calorie intake wants of the body will also change.”

Mental health is a vital part of the process

Palu partially credits trauma and poor mental health for her weight struggles. She says that The Biggest Loser was the first time she addressed that, which she believes led to her success. “I feel like the show for me was like peeling an onion, like I had all these layers that I was just peeling off,” she says. “There was a lot of stuff I got to just dig out and throw out of my body. So I did walk away with a much clearer mental state.”

There was a counselor on the show that she interacted with, although she wishes she got more time with him. “I wish I had also gone to therapy after the show and continued that journey, because I was still not mentally healed and needed that extra help to continue to be successful,” she says.

Hibbard, on the other hand, is among other former contestants who feel they left the show in a worse mental state than they came. “Make no mistake, The Biggest Loser dehumanizes its participants and studies have shown that it makes viewers less empathetic to people in larger bodies as well,” says Hibbard.

Some experts agree. In 2016, Dr. W. Scott Butsch, the director of obesity medicine in the Bariatric and Metabolic Institute at the Cleveland Clinic, told the Cut, “I almost think the show is some sick way of just mocking people who have obesity.”

This is largely because of the way in which “producers gamified weight loss,” Jillian Michaels, an original trainer on the show, told TODAY. She believed that contestants needed more support than they received. “The Biggest Loser needed a mental health professional. I think there was some random guy they could talk to if they needed, but these people needed deep work.”

Even still, she told Women’s Health U.K. that she doesn’t agree with some other criticism that the show has received. “I think the world has shifted to a place where that format and messaging is considered fat shaming. But it isn’t, and it’s not meant to be,” she said in 2019.

While some contestants, like Palu, have found the show to be helpful, Anekwe acknowledges how important it is that the conversation around weight has evolved. “With the pervasiveness of weight bias, we should definitely be encouraging more holistic and health-centered approaches to weight loss,” she says.