Key Topics Covered

This episode delves into a 2016 study titled “Persistent Metabolic Adaptation 6 Years After The Biggest Loser Competition,” which examined participants from season 8 of the show, which aired in 2009. We will also touch on insights from a 2022 follow-up study, “Energy Compensation and Metabolic Adaptation: The Biggest Loser Study Reinterpreted.” When you think about how extreme the weight loss measures were on The Biggest Loser, it’s easy to imagine that these studies uncovered some fascinating and novel findings about the participants’ long-term metabolic changes.

The Study Itself

  • Of the 16 participants in the competition, 14 agreed to the follow up study.
  • Resting Metabolic Rate (RMR) was measured using indirect calorimetry at baseline at the end of the 30-week competition and 6 years later.
  • Metabolic adaptation was defined as the difference between their actual RMR and what a formula would predict.
  • Participants lost an average of 58.3kg during the competition.
  • On average, they regained 41kg over the 6 years.
  • Before the competition, their RMRs fit what you would expect with a formula. After the competition, it was 500 calories lower than a formula would predict.

Interpretations of This

  • In seeing that data you could probably start to interpret a RMR that is 500kcal lower than predicted to basically be the equivalent of “perpetually dieting with a 500kcal deficit” just to maintain weight.
  • It is worth acknowledging that participants’ RMR was still averaging 1900kcal. It’s just that the prediction would be 2400kcal.
  • Many people in the fitness industry interpreted this as a bit of a sign that “metabolic damage” occurs where there is a long-lasting effect from dieting, particularly crash dieting.

Metabolic Adaptation Findings In Other Research

  • Interestingly, pretty much every other study looking at metabolic adaptation finds that it reverses when calories are raised.
  • It doesn’t usually take long either e.g. ~4 weeks at maintenance and usually it is non-existent.
  • You could argue that bigger weight losses likely take longer for it to return to baseline. But the participants in this study averaged a small-moderate surplus for 6 years. 
  • Either way, this study is a huge outlier.

If It’s an Outlier, Why?

  • There are a few ways to explain why this study is such an outlier.
  • One explanation that people have highlighted is that the rate and volume of weight loss might have played a role. It was extremely rapid and involved major caloric restriction and over-exercising.
  • Whilst there isn’t as much research as we would like looking at metabolic rate alongside things like bariatric surgery, the data we do have does not make us think that this explanation fits well because this would also be a scenario where weight loss is very rapid. 
  • The biggest loser study participants also retained fat-free mass exceptionally well due to the amount of exercise they were doing. So that is one key difference. 
The biggest loser contestants on treadmills exercising

Follow Up Study

  • Kevin Hall, who was one of the original authors, completed a narrative review in 2021, trying to explain why it’s such an outlier
  • In this paper, a few things were brought up:
  • The first one is that he discussed how the data had been misinterpreted as evidence that “diets destroy your metabolism and most lifestyle interventions are doomed to fail… even though the participants in the study still had maintained a clinically meaningful average of 12% weight loss after 6 years.”
  • The next thing he highlighted was that high physical activity can lead to a reduction in energy expenditure elsewhere.
  • This is known as the constrained energy expenditure model.
  • The participants with the highest physical activities 6 years later also experienced the most measurable decreases in RMR, which supports this idea.

Summary

  • It’s an interesting study, but arguably, the nutrition and fitness world would be simpler if it didn’t exist. 
  • It’s a huge outlier, and trying to take useful information without awareness of all the other research can lead to big misinterpretations.
  • The constrained energy expenditure model could explain these findings. But even if they don’t fully cover it, I still wouldn’t read into this too much.


Relevant Blogs/Research

Relevant studies:

Persistent metabolic adaptation 6 years after The Biggest Loser competition – PMC 

Energy compensation and metabolic adaptation: “The Biggest Loser” study reinterpreted

Metabolic Adaptations to Weight Loss: A Brief Review 

Relevant blog posts:

What Is Metabolic Adaptation and Why Does It Occur? Everything You Need to Know