Adaptive Thermogenesis — The Beauty and the Beast of The Biggest Loser

TAGS: the biggest loser, Non-Exercise Activity Thermogenesis, Resting Metabolic Rate, Adaptive Thermogenesis, slow metabolism, calorie restriction, Starvation Mode, Calorie Intake, brandon patterson, weight gain, weight loss, strength training

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"Starvation Mode" is the concept of the body overreacting to calorie restriction—you eat less, and suddenly your metabolism slows down to offset the reduced intake of food. Pushed to its extremes, the metabolic drop might be so great that you can gain weight even while reducing calories.

It’s catchy, but like most memorable fitness phrases "Starvation Mode" is not very accurate. For this article, I’ll stick with Adaptive Thermogenesis (AT) as our working topic, as this more inclusive term provides a clearer picture than the popular alternative. If we think of most modern metabolism formulae as using some sort of combination of age, weight, the thermic effect of digesting food, and activity (i.e., easily measured/postulated variables) to arrive at a person’s likely metabolism, then AT would be the sum total of every not-included variable that throws off these calculations.

Since the items not included are hard to measure and generally lumped in with your Resting Metabolic Rate (RMR), AT is generally conceived (though not exactly technically perceived) as alterations to you RMR. About 80% of RMR comes from internal organ activity, so there’s a trend towards reconceiving AT as being more about measurable physical changes to organs directly related to calorie intake than it is about subtle adjustments that scale beyond calories. There’s also strong evidence that our daily activity simply slows down in response to caloric restriction, and that much of AT can be explained via this mechanism. Technically known as Non-Exercise Activity Thermogenesis (NEAT), NEAT reductions can manifest in everything from unconsciously slouching more while sitting, to walking more slowly than usual, to fidgeting less.


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To what extent AT exists as something within metabolic pathways, we’re likely looking it as a sort of broad "symptomatic" response by many individual bodily functions to the act changing caloric intake, ranging from (and intertwining with) hormones, to nervous system activity, to minute improvements in movement efficiency. It seems the AT ‘dial’ can turn both ways, e.g., it can negatively act against energy expenditure by possibly improving movement efficiency, or it can respond to circadian cycles to raise the thermic effect of a meal.[i]

(As an additional note, AT isn’t the only example of adaptability in the human digestive/metabolic process; reducing your protein intake will reduce protein-related/dependent cell turnover and enzyme production regardless of total calorie ingestion.)

For both health and physique reasons, most concern lies with negative AT, particularly 1) the extent to which it depresses RMR, 2) the duration of the negative impact, and 3) its ability to be overcome. A new study on participants in “The Biggest Loser” reality show[ii] has put these concerns back in the public eye. The attention it’s getting is more about the show than the everyday value of the science found in the paper. In fact, the extreme nature of “The Biggest Loser” (TBL) means the study is basically helping build a theoretical endpoint for AT.

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The beauty of “The Biggest Loser” (at least in terms of studying AT) is its combination of severe methods with an extremely overweight subject group. The show demands as much as 13 weeks of intense near-daily exercise and calorie restriction from contestants; the contestants themselves can (and do) undertake additional measures off-camera in the 17 weeks between taping and the final episode, including extra exercise, dehydration, and supplement usage. The result is that winning contestants routinely cut their bodyfat percentage by 30 – 40%, or as much as 200 pounds each, depending on starting weight.

The NIH team running this study designed it as a six-year follow-up on sixteen TBL contestants they previously monitored as part of a prior study[iii] conducted while they were part of the show.  So really, making sense of the latest study means we have to look at the earlier one.

The First Study

While the nature of the show prevented all sixteen contestants from advancing uniformly through the season, most kept up with intense dieting/training regimens that allowed for relative sample uniformity. On day one, the average bodyweight for these contestants was 149 kilograms. By the end, it was 92 kilograms. In other words, it might be the most intense weight-loss environment studied since Ancel Keys starved conscientious objectors back in WWII.

The weight loss came with a price for the TBL participants: the team found that, on average, the contestants’ respective Resting Metabolic Rates had declined by 500kcal/day more than their general weight loss or specific loss metabolically-active tissues would warrant, indicating that this deficit was caused by AT. More weight loss led to a concordantly greater reduction in RMR.

Though not the goal of their research, the team’s post-intervention testing pointed to depressed leptin and thyroid activity as at least part of the AT pathway in these contestants, though they couldn’t confirm/rule out depressed CNS activity.  Altered levels of adiponectin, hormone with many metabolic functions, also stood out, but the team couldn’t do much with the data.

The Second Study

Fast-forward six years, and the researchers make a follow-up call on these participants, fourteen of whom agree to participate. Just looking at average weight, the participants went from 92 kilograms at the end of the contest to 131 kilograms at the follow-up. Their bodyfat percentages likewise tracked almost back to pre-contest levels: 49% at start, 28% at contest completion, and 48% at follow-up.

The team concluded that a return to a normal lifestyle likely wasn’t the sole contributor to their weight regain. As has been widely reported, despite the near-complete return to their starting weights, the average 500kcal/day metabolic deficit remained, and was even worse with contestants who kept the most weight off.  For whatever reasons, their AT seemed to have a shelf-life of at least six years, or well after the ‘starvation’ ended. This represents not only a sizeable weight-loss obstruction, but a big counterpoint to prior research indicating that downregulations in non-exercise activity (and not RMR) are prime contributors to post-metabolic decline.

There are a few caveats to this conclusion. A notable (but relatively small) example is that two of the fourteen contestants experienced an AT upswing of a few hundred calories in the period between the contest ending and the six-year follow up. Unfortunately, the study doesn’t do much in the way of individualizing data, so it’s hard to be an arm-chair dietician and tease out what happened with these two folks.

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This lack of individualization also swings into a second, larger problem in that both the normalizing period and a Total Daily Energy Expenditure (TDEE) test period were each only two weeks long and not well controlled. The big weakness here is that the participants weren’t overseen by the researchers, which opens the door for a four-week period for participants to modify their behavior in response to the act of weighing themselves. Though it might seem small, during the normalizing period the contestants were told to weigh themselves every day via an internet-connected scale for a two-week period, with the intent of “normalizing” their weight and body composition. With the constant weight reminders (and the specter of an intensive, three-day round of follow-up DEXA, RMR, etc., testing at a central laboratory), it’s very possible the participants consciously or subconsciously modified their exercise or eating habits. The same could’ve happened during the second two-week period, when the contestants self-collected daily urine samples for measuring TDEE.

Coach and nutritionist James Krieger noticed an indicator of this phenomenon when looking at the two-week weight data. On average, the contestants lost about a pound of weight during the two-week period, leading him to think the participants bumped up their physical activity levels during the intended normalizing period.[iv] The paper does chart the weight fluctuation of individuals over the course of the two-week period. Looked at this way there were some fairly extreme fluctuations of roughly +/- 3 kilograms among some participants occurring within a span of several days, and while it’s hard to tell from looking at the chart, it looks like nearly all of the contestants had a weight dip towards the end of this period.  “Smoothing” this data wasn’t (and wouldn’t be) problematic in the sense of “doing the math,” but I’m not convinced this change was as insignificant as reported in the paper.

One final aspect that I find myself questioning is the paper’s statement that “after six years, TEE increased but remained below baseline while physical activity was not significantly changed since the end of the competition.” I have a very hard time believing that in the six years elapsing between a grueling, high-stakes weight-loss contest and a resumption of normal life that there were no significant changes in the contestants’ physical activity levels. It seems likely this too falls on the imprecise nature of self-reporting.  I’m going back and forth on just how much this affects the paper’s conclusions, but it stands out.

For all these issues, I’m not convinced there was a 1:1 relationship between this study’s findings and what is really going on with these contestants. Would I be surprised if similar subsequent papers found long-term declines in AT? No, but nor would I be surprised if findings authored under more controlled circumstances found the decline to be far less significant. Add in the extremity of the weight loss protocols followed by these contestants, and it seems that this study isn’t especially useful to the general public, even in the limited sense of being an upper-bound to negative AT.


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Returning to the big picture, If we take this study’s results as a face-value upper-bound, an intense, multi-month period of strenuous diet and energy-system exercise could put you at a long-term metabolic deficit that ranges somewhere between a large snack and a full meal, depending on your current metabolism; this deficit could increase along with weight loss, and stay constant relative to weight that’s kept off.

But what happens with tough, yet less extreme measures? One team took a swing at a mini-version of the Minnesota Starvation Experiment, where non-obese participants experienced four weeks of intensely fluctuating diet: a one week overfeed of +50% of maintenance calories, followed by three weeks at -50%, followed by a two-week refeed at +50%. With the benefit of stricter controls than the TBL work, the results were that 60% of participants experienced negative AT of about 100kcal/day when adjusted for changes in muscle, organ, and tissue mass; the AT took the form of lowered heart, kidney, and temperature function, and increased creation of glucose in the liver. The key point for us is that the final two-week overfeed mostly reversed negative AT.[v]

Coupled with a body of prior research that suggests strength training and high protein intake as factors that can offset AT, and similar evolving work indicating diet-cycling isn’t as harmful as often purported to be, this paper paints a more promising  (and likely more precise) picture of the body during caloric restriction. While it might’ve been more useful for our purposes if it had provided a baseline refeed rather than an overfeed, its results are much more pertinent for most people than results based on TBL participants.

Wrapping Up

I put Adaptive Thermogenesis on my articles to write list months before this latest TBL study — the sheer reach of the study prompted me to jump on the topic ahead of time, and likewise prompted me to pay an inordinate degree of attention to it. The takeaway for me from all of this is that Adaptive Thermogenesis isn’t perhaps the boogeyman it’s been made out to be in the press and popular publications; for my money, the more worrisome long-term changes brought about by calorie restriction are those that involve in our hunger/satiety wiring.


[i] More on this to come in a later article.

[ii] Fothergill, et al. Persistent Metabolic Adaptation 6 Years After “The Biggest Loser” Competition. Obesity (2016) 00, 00-00.

[iii] Johannssen et al. Metabolic Slowing with Massive Weight Loss despite Preservation of Fat-Free Mass. J Clin Endocrinol Metab 97: 2489–2496, 2012

[iv] Taken from a presentation by Krieger, as transcribed in Alan Aragon Research Review, Oct/Nov 2016.

[v] Muller, et al.  Metabolic adaptation to caloric restriction and subsequent refeeding: the Minnesota Starvation Experiment revisited. Am J Clin Nutr 2015;102:807–19.

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