The Biggest Loser Study

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This article was written by Associate Nutritionist and Student Dietitian Sarah Hall and was reviewed by Registered Dietitian Maeve Hanan.  

Who can forget The Biggest Loser? I endured season after season, watching in awe as contestants were put through the mill by Jillian Michaels and Bob Harper, who went on to host it. Michael’s famously saying, “I’m proud I made them vomit”, and “The only way you’re coming off this damn treadmill is if you die on it!”.

Unbelievably this show ran over 11 seasons in Australia, 5 in the UK and 18 in the US, albeit with a ‘lighter’ less competitive version in 2020.

What Was The Show About?

The show’s premise was for contestants in bigger bodies to lose the most weight over a 30-week competition through severe calorie restriction and up to six hours a day of strenuous exercise. As a result, many competitors lost vast amounts of weight, some up to 50% of their initial body weight. The final episode culminated with a big reveal and final weigh-in, where the winner walked away with a large cash prize.

For example, in 2009, season 8, Danny Cahill won $250,000, and for a couple of years, he was able to keep the weight off, albeit through excessive amounts of daily exercise. However, once real life got in the way and he started a new job which meant he was more sedentary, the weight started creeping back up. 

What Did The Study Find?

Season 8 was a significant year for the show as the contestants participated in a long-term study to document the change in their resting metabolic rate (RMR) and body composition (1).

This is the longest study to date investigating the impact of dieting and weight loss on metabolism.  

The sixteen contestants underwent various measurements at baseline and again at the end of the 30-week competition. Fourteen of the contestants participated in the 6-year follow-up as well. 

Changes in Body Composition

 Body composition was measured by dual-energy X-ray absorptiometry (i.e. a DEXA scan).

Before the competition started, the contestants weighed 148.9 kg ± 40.5. At the end of the show, the contestants lost 58.3 kg ± 24.9.

BUT after 6-years, only one of the contestants maintained the weight loss.

The remainder regained varying amounts of weight, and the mean weight was 131.6 kg ± 45.3, which was just 11.9 kg ± 16.8% different from baseline.

Five contestants regained all (within 1%) or more of their original weight. 

Resting Metabolic Rate 

In this study, RMR was measured using a technique called indirect calorimetry.

Our total metabolic rate is the total energy expenditure our body needs to maintain the same weight. This includes: 

  • Resting Metabolic Rate (RMR) or Basal Metabolic Rate (BMR) is the number of calories our body requires when entirely at rest, and includes the energy required for breathing, blood circulation, organ functions, and other bodily functions. Our BMR makes up 60-70% of the total calories we need daily, even if we didn’t get out of bed!
  • The Thermic Effect of Food (TEF) is the energy required to digest, absorb and metabolise food.
  • Non-Exercise Activity Thermogenesis (NEAT) is the energy expended living our lives, including typing, gardening, housework, and even fidgeting.NEAT will vary depending on the job we do or how we spend our leisure time. 
  • Exercise Activity Thermogenesis (EAT) includes the structured exercise we intentionally engage in.

Total metabolic rate is very individual based on sex (men tend to have a higher BMR due to having more muscle mass on average) and age (our BMR reduces as we age due to a reduction in muscle mass). So it’s never one-size-fits-all!

Remember, when the contestants signed up for the show, they had normal metabolisms for their size with an RMR of 2,607 kcal/day ± 649. So when they lost weight, it made sense that their metabolism would reduce; after all, they wouldn’t need as many calories to sustain a new smaller body. 

However, the researchers were surprised to find their metabolisms had reduced more than predicted.

In fact, their RMR dropped to 1,996 kcal/day ± 358 as opposed to 2,272 kcal/day ± 435, which was 275 kcal/day ± 207 less than the scientists had expected. This slowing of metabolism is called metabolic adaptation, otherwise known as adaptive thermogenesis.

Changes in Fullness Hormones

Leptin is often called the ‘fullness’ or’satiety’ hormone, as it sends signals to the hypothalamus, letting you know you are full. Leptin is responsible for energy balance and is secreted from fat cells; therefore, if fat increases so does leptin and as fat decreases, leptin also does.

High leptin levels reduce appetite allowing the body to use fat stores and low leptin levels promote overeating as a survival mechanism. 

At the end of the competition, leptin had reduced dramatically from an average of 41.14ng/mL ± 16.91 to 2.56 ng/mL ± 2.19. 

What Happened at the 6-Year Follow-Up? 

If their RMR reduced when they lost weight, surely it would go up again if they regained the weight? 

RMR didn’t return to normal when they regained weight.

The contestant’s metabolism didn’t recover and actually continued dropping, even though their weight kept increasing. 

At the 6-year point, their RMR was 1,903 kcal/day ± 466, which meant that even though some of the contestants were back up to their original weight, they had to eat on average 500 calories less a day than they could before the competition, to maintain their weight. 

After six years, metabolism slowed the most in the contestants who had lost the most weight and those who had managed to maintain weight loss. It slowed to a lesser degree in those who had lost a more modest amount of weight. 

This study also demonstrated that even after six years, leptin levels had increased again to 27.68 ng/mL ± 17.48, but this was still below the contestant’s pre-competition level of 41.14ng/mL. This means that they were likely to experience hunger more often, even six years after participating in the show and losing weight.

Although this study followed the contestants from one US season, contestants from other seasons have met the same fate. Ryan Benson from season 1 weighed more in 2017 than in 2004 when the show originally aired. (2) Inevitably, he felt guilty and blamed himself for the weight regain. Unbelievably, the experience of The Biggest Loser didn’t deter him and some other contestants who had also gained the weight back as they signed up for another show entitled ‘The Big Fat Truth’. 

Some contestants have admitted carrying out unhealthy and sometimes dangerous behaviours to secure their win. Ryan revealed he gained 14.5kg within five days of the final, just from drinking water. He admitted he was so dehydrated he was urinating blood. (3) Outspoken critic Kai Hibbard revealed eating only sugar-free jelly and asparagus, and spending the night in and out of the sauna before the weigh-in for the final, where she became runner-up of season 3. (4)

And of the contestants who successfully kept the weight off, it’s no surprise to discover that some have done so by engaging in some very disordered habits. For example, Kelly Minner from season 1 expressed that she exercises for up to 4 hours, six days a week (5). Unfortunately, for most people, this is neither achievable nor advisable and is associated with symptoms of eating disorders (6).


This research carried out on The Biggest Loser included a very small sample of sixteen, and as with the Minnesota Experiment, the participants lost weight under extreme circumstances. 

What Can We Take From This Study?

Bodies are pretty clever at protecting us. They don’t know if we are trying to drop weight to win $250,000, get married, go on holiday or for our ‘health’. When dieting, leptin levels decline, which signals to the hypothalamus to stimulate the need to eat, reduce energy expenditure and promote weight gain as a survival mechanism. 

When we lose weight, we should expect our overall energy needs to be less, but whether or not metabolic adaptation contributes to weight regain is debatable. Research into metabolic adaptation has thrown up mixed results, with research suggesting it is not a barrier to weight-loss maintenance.

Martins et al. followed 171 women with a BMI of 28.3 ± 1.3 at baseline following an 800 kcal liquid diet until their BMI was below 25. Body weight, body composition and RMR were measured after a 4-week maintenance phase following initial weight loss and at the 1 and 2-year points. Participants initially lost 12 ± 2.6 kg, but by year one had regained 52% ± 38% and 89% ± 54% by year two. After initial weight loss, metabolic adaptation was 50–60 kcal/d below predicted levels; however by two years there was no metabolic adaption (7).

It is understood that the level of metabolic adaptation corresponds with the level of weight loss, and in The Biggest Loser, this was extreme.


  1. Fothergill E, Guo J, Howard L, Kerns JC, Knuth ND, Brychta R, Chen KY, Skarulis MC, Walter M, Walter PJ, Hall KD. Persistent metabolic adaptation 6 years after “The Biggest Loser” competition. Obesity. 2016 Aug;24(8):1612-9.
  2. [Accessed Aug 2022]
  3. [Accessed Aug 2022]
  4. [Accessed Aug 2022]
  5.,28804,1626795_1627112_1626456,00.html. [Accessed Aug 2022]
  6. [Accessed Aug 2022]
  7. Martins C, Gower BA, Hill JO, Hunter GR. Metabolic adaptation is not a major barrier to weight-loss maintenance. The American journal of clinical nutrition. 2020 Sep 1;112(3):558-65.


Maeve has been consulting on The Food Medic Educational Hub for 12 months now and has been a huge asset to the team. Her ability to translate some very nuanced topics in nutrition into easy-to-follow, informative articles and infographics is really admirable.

Dr Hazel Wallace

Founder of The Food Medic

Maeve is incredibly talented at sharing scientific information in an easy to understand way. The content she shares with us is always really interesting, clear, and of very high quality. She’s one of our favourite writers to work with!

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Senior UX Writer at Thriva Health

Maeve has written extensively for NHD magazine over the last few years, producing a wealth of dietetic and nutritional articles. Always evidence based and factual, Maeve creates material that is relevant and very readable. She provides high quality work with a professional and friendly approach. Maeve is a beacon of high quality knowledge and work within the nutrition writing community; and someone NHD magazine is proud to work with.

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