We’re big proponents of safe and sustainable weight loss. But with fad diets, cleanses, and even television shows like The Biggest Loser promoting rapid results, it can be hard to understand why.
A look at The Biggest Loser
First aired in 2014, The Biggest Loser is an American reality show that features individuals with a BMI of 40 or greater who compete to win a $250,000 cash prize by losing the highest percentage of weight relative to their starting weight.
The show operates around a simple premise: In order to lose weight, one must simply burn more calories than they eat. But we know weight loss isn’t that straightforward.
For 30 weeks, contestants complete up to seven hours of exercise and consume as little as 1,000 calories per day. That results in weekly weight losses of 10 to 30 pounds for most contestants.
The consequences of rapid weight loss
Various studies of long term weight loss show that, on average, greater than 50% of the weight people initially lose is regained within 2 years and, on average, more than 80% of the lost weight is regained by 5 years.
And it’s not just because of some issue with willpower or discipline.
In both those with and without obesity who are working to lose weight, research has shown that there are biological changes — in particular related to our metabolism — that create a powerful opposition to maintaining weight loss.
Metabolism is a term that describes all of the bodily processes that turn the food we eat into energy. This energy is used for everything — from brushing our teeth to powering our morning jog. Our metabolism works around the clock and it’s constantly adapting. A number of biological factors — like age, gender, muscle mass, genetics, and gut bacteria — influence our metabolism.
Our bodies are smart, and they’ve evolved to be very efficient at protecting our energy stores to increase our chances of survival, meaning it’s much easier to gain energy/weight than it is to lose it. When we lose weight, a large component of our metabolism — our resting metabolic rate (RMR) — slows. Our RMR fuels basic essential functions while the body is at rest, like breathing and circulating blood, and naturally slows down because a smaller body requires less energy to function.
The body’s ability to self-adjust and counter weight loss by slowing RMR is known as "adaptive thermogenesis” or “metabolic adaptation.” This explains why weight loss is much more complex than the “calories in versus calories out” equation.
What happens during metabolic adaptation?
During metabolic adaptation, there are many more components of the equation at play.
Your total daily energy expenditure (TDEE) is the total number of calories you burn or use in a day, and makes up your “calories out.” It’s composed of:
- Resting metabolic rate (RMR), the energy used to carry out basic but essential functions at rest like breathing and circulating blood (~70% of TDEE),
- The thermic effect of feeding (TEF), the energy used to digest food (~10% of TDEE),
- Non-exercise activity thermogenesis (NEAT), the energy used during activity that doesn’t involve structured exercise such as walking to work, cleaning, typing, doing yard work, fidgeting, etc. (~15% of TDEE),
- Exercise activity thermogenesis (EAT), the energy used during structured physical activity (~5% of TDEE).
Following weight loss, shifts in these metabolic components take place, but more on that later.
So, what happened to contestants on The Biggest Loser after they experienced rapid weight loss?
A 2016 study in the journal Obesity measured changes in body composition and RMR in contestants from one season of The Biggest Loser six years after the competition. The 14 subjects who participated in the study lost an average of 129 pounds at the end of the 30-week competition, but what happened years later?
They gained weight:
Most contestants regained a significant amount of weight, and five contestants were within 1% of their baseline weight or above six years later. Despite this regain, many contestants maintained a clinically meaningful average of ~12% weight loss. On average, contestants maintained a high level of physical activity from the end of the 30-week competition to the follow-up 6 years later. This high rate of physical activity may help to explain the weight loss that was maintained.
Their resting metabolic rate reduced after they lost weight, and stayed reduced after they gained it back:
Contestants’ RMR decreased from an average of 2,607 calories per day on Week 1 of the competition to 1,996 calories per day on Week 30. It makes sense that they were burning fewer calories by Week 30 because they had smaller bodies — and smaller bodies require less energy.
What was unexpected and fascinating is that contestants’ RMR stayed low at 1,903 calories per day even six years after the competition — they burned fewer calories even after they regained weight. This suggests that metabolic adaptations of weight loss continued after weight loss had reversed.
A 2021 follow-up review looked into why this could be. The reviewers suspected that these changes in contestants’ metabolism could be explained by the constrained energy expenditure model. This model suggests that small increases in physical activity lead to small increases in the number of calories burned — but only to a certain point.
The body reaches a threshold and adapts by reducing the amount of energy it uses in other non-essential activities. (Remember how we said our bodies are smart?) For example, if you start running everyday you may be burning an extra 200-500 calories, but your body will compensate by burning fewer calories in other areas.
They experienced changes in hormones that regulate hunger and metabolism:
Leptin, also known as the “satiety” or “fullness hormone,” helps to maintain your weight by regulating food intake and energy expenditure.
Leptin levels are directly related to fat mass — as fat mass increases, leptin levels increase to suppress appetite. When fat mass decreases, which typically happens when you lose weight, leptin levels decrease resulting in increased appetite and decreased energy expenditure. In other words, when you lose weight, you will experience more hunger and burn fewer calories.
As expected, when contestants lost weight, leptin levels decreased. Interestingly, however, six years following the competition, their levels didn’t return to normal even after they regained weight. Contestants ended up hungrier than before they started.
Key takeaways:
- When you lose weight, your body adapts and responds. Your metabolism slows so you burn fewer calories, and leptin decreases so you feel hungrier. Your body is naturally built to resist losing weight. This is part of what makes long-term sustainable weight loss so challenging.
- Metabolic adaptation in weight-stable individuals following long-term weight-loss interventions is typically much smaller than what has been observed in The Biggest Loser contestants. Contestants on the show represent an extreme case of rapid weight loss.
- Six years after the competition, contestants on The Biggest Loser gained most of the weight they lost back. However, they continued to experience decreased metabolism (including RMR and TDEE), and changes in hormones like leptin, which make maintaining their weight loss difficult.
Why slow and steady weight loss wins the race (or, in the case of The Biggest Loser, the competition)
Drastic weight loss in a short amount of time comes with a price. Research shows that gradual weight loss preserves RMR, the major part of your metabolism, and promotes more fat loss compared to rapid weight loss.
While The Biggest Loser is an extreme example of quick weight loss, many diets and cleanses promote rapid weight loss as a selling point. “Lose 10 pounds in 10 days” is a promise that’s hard to resist! Unfortunately, in most cases you’ll gain the 10 pounds (or more) back just as quickly. We call this “weight cycling” and it can be a rough experience both physically and mentally.
Instead of focusing on the biggest amount of weight loss, we like to focus on safe and sustainable weight loss.
If you ask us, setting an achievable behavioral goal sets you up for success better than the 7-hour gym session you can only maintain for a week in an isolated environment (with celebrity trainers no less!).
What is considered “healthy” weight loss? We believe that a safe and sustainable weight loss is, on average, 1-2 pounds per week. This safe and sustainable approach helps to preserve your muscle mass, protect your metabolism, and avoid those hormonal swings.