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Primer on Obesity and Medical Management Pt IV. The Biggest Loser Study: Understanding Resting Metabolic Rate and Metabolic Adaptation

Updated: Jun 12

In our blog series so far, we’ve delved into the roles of ghrelin, leptin, insulin, and incretins in regulating appetite, satiety, and hunger. Today, we shift our focus to the concepts of resting metabolic rate (RMR) and metabolic adaptation, using the well-known TV show "The Biggest Loser" as a case study to illustrate these phenomena. This will, hopefully, help explain plateaus during weight loss programs and weight regain following weight loss, and why the concept of "calories in, calories out" is a little more complicated than you think.

Remember-- it's all about energy

Remember that the basic, underlying principle of this blog series is that the body is hard-wired to protect its energy stores. The body's main storage of energy is fat. The body will protect fat and therefore resist weight loss. It is instinctual. Always remember this when you are strategizing and coming up with ways to lose the weight.

Total daily energy expenditure

Total energy expenditure (TEE) is the amount of energy a body uses in a 24-hour period and it is made up of three main components: resting metabolic rate, thermic effect of food, and physical activity (made up of both non-exercise activity thermogenesis NEAT and exercise activity thermogenesis EAT).

TEE = RMR + TEF + (Non-exercise physical activity + Exercise physical activity)

Resting Metabolic Rate

The thermic effect of food is the amount of energy the body uses to digest, absorb, and metabolize food. It takes different amounts of energy for different macronutrients (carbohydrates vs proteins vs fats). More specifically, eating foods with a high TEF can help burn more calories. Some foods with high TEF include: lean meats, eggs; fibrous vegetables like spinach, broccoli, and kale; and whole grains like brown rice, quinoa, and oats. Physical activity is broken into non-exercise activity thermogenesis (NEAT) (such as fidgeting, walking around the office, typing, taking the stairs) and exercise activity thermogenesis (EAT) (such as jogging, Zumba class, swimming laps). Resting metabolic rate (RMR) is the amount of energy that your body requires to maintain basic physiological functions while at rest. This includes breathing, circulating blood, and maintaining body temperature. RMR accounts for the largest portion of your total daily energy expenditure.

If the amount of energy entering a system = the amount of energy being used by a system, the net amount of energy is (theoretically) zero, right? If the calories used each day is supplied by the exact number of calories we consumed in our diet each day, then there would be no extra calories to store or use.

If the amount of energy entering a system is MORE than the amount of energy being used by a system, the excess energy is stored away for future use. In the case of calories, the excess is stored as fat.

If the amount of energy entering a system is LESS than the amount of energy needed by the system, the additional energy required is found from previously stored away energy-- the stored fat.

So the concept of fat loss should be simple. If we force an energy deficit, i.e., if we force a scenario in which the amount of energy entering a system is less than the amount of energy needed by the system, the system will be forced to use fat. The name of the game then is CREATE AN ENERGY DEFICIT.

But you didn't think you could outsmart your body that easily did you? There's another concept to learn: Metabolic adaptation.

Stop me if you've heard this story before. You start diet #1 because you heard great things about it from a friend and you do great! You lose 20 lbs and you're feeling pretty good. After about a month, it's getting a little harder to keep that weight loss going and you start seeing the weight come back... and then a little more. After a while (months? years?) you realize that now your weight is actually higher than it was before you started diet #1, so you are going to try something different with diet #2 and you do great again! You lost 25 lbs this time and you're feeling great again and this time you think that this is the one. But after a while, you start seeing the weight loss slow down and now you're only losing about a pound every two weeks and before long you are back to your starting weight and then in a few months, you're at a higher weight than before. And so on, and so on.

Metabolic Adaptation

Metabolic Adaptation refers to the process by which the body adjusts its total energy expenditure in response to changes body weight. The body does not like losing its energy stores, so it has to figure out how to stop expending so much energy. Many things happen when there is a loss of weight, particularly when there is an abrupt, large loss of weight.

1. The body decreases its resting metabolic rate. This actually makes sense. If there is less of you, then the body requires less energy to fuel physiologic processes like breathing or maintaining body temperature or circulating blood.

2. There is a decrease in energy generated from physical activity. Even though you may be exercising regularly and moving more, because you are 'smaller', the energy expended to move a smaller amount of weight is overall less.

3. The energy generated from the thermic effect of food is less because you eat less.

4. Remember leptin is released from fat cells to serve as a satiety signal to the brain. If there is a loss of fat, there is a loss of leptin and therefore a loss of the satiety signal. The more weight you lose, the hungrier you become.

5. One of the triggers of ghrelin release from the stomach is a decrease in calorie intake. Ghrelin is the appetite hormone. The lower the calorie intake, the increase in appetite.

When you lose weight, your body's natural response to perceived energy deficits is aimed to conserve energy and resist further weight loss.


The Biggest Loser Study: A Case of Extreme Metabolic Adaptation

"The Biggest Loser" was a reality TV show where contestants competed to lose the most weight through intensive diet and exercise regimens. While the dramatic transformations were inspiring, a study conducted on the contestants revealed some concerning findings about the long-term impacts of extreme weight loss on metabolism.

Researchers followed 14 participants from Season 8 of the show for six years after the competition. There were two major findings of this research study:

1. Participants experienced significant metabolic adaptation, meaning their resting metabolic rate (RMR) dropped substantially as a result of the weight loss (not unexpected) but was lower than expected for their body size (unexpected).

2. Additionally, this metabolic slowdown persisted even six years after the competition, making it harder for them to maintain their weight loss.

In the example above, you'll see a 46 yo woman who is 5'4" at 200 lbs. Using available RMR calculators, her RMR is estimated to be 1600 cal/day. After a 40 lb weight loss, now at 5'4" and 160 lbs, her estimated RMR should be 1400 cal/day however, when actually measured, her RMR was lower by 200 calories at 1200 cal/day. Two women with the same measurements (both 5'4" and 160 lbs) had different RMRs-- the woman who had just reached 160 lbs by recent weight loss had a significantly lower RMR than a woman of the same height who was already 160 lbs and had not had recent weight loss.

Why? Perhaps the best explanation for this is the survival instinct. For the woman who had lost the weight, her metabolic rate had to adjust to a loss in weight and energy and therefore lowered the rate at which it was utilizing its energy stores. For the other woman, there were no perceived threats to her energy stores therefore there was no need to adjust the metabolic rate.

Why is this important? Because, for the woman who has just lost 40 lbs, she now has to overcome a greater calorie gap to continue losing weight. Remember, if the name of the weight loss game is to CREATE AN ENERGY DEFICIT, and Calories consumed has to be < total energy expenditure, AND now your RMR has just decreased, THEN either NEAT, EAT or TEF have to increase to compensate for the decrease in RMR or the calories consumed has to be much less than it was before the RMR was reduced. Let's put this into perspective: If you are the woman in the example and you are 5'4" 200 lbs, and you have just lost 40 lbs and now weigh 160 lbs, then you are starting to feel great! You feel like you are really on a roll and you finally have a handle on your diet and exercise. But, suddenly, your weight loss stalls. You hit a plateau. You aren't losing any more weight even though you haven't changed anything. You are still eating the same amount of calories and you are still working out the same number of days as before. What is happening?! Why aren't you losing any more weight? Well... now your RMR has decreased so your TEE is LESS everyday and you didn't even know it, so you are no longer the calorie deficit you thought you were in.

The Implications of Metabolic Adaptation

The Biggest Loser study highlights the challenges of maintaining weight loss, particularly after extreme dieting and exercise. The significant reduction in RMR means that individuals have to consume fewer calories and engage in more physical activity than someone who has never lost weight, just to maintain their new, lower body weight. This metabolic adaptation can make weight maintenance extremely difficult and increases the risk of weight regain. The study underscores the importance of really understanding sustainable weight loss practices.

Beyond "Calories In, Calories Out"

The insights from the Biggest Loser study emphasize that weight loss is more complex than the simple equation of "calories in, calories out." This traditional concept fails to account for the body's adaptive responses to weight loss, such as the decrease in RMR. Hormonal changes, metabolic adaptation, and individual variability all play significant roles in how the body manages weight. Recognizing these factors is crucial for developing effective, personalized weight management strategies that go beyond calorie counting and consider the broader physiological landscape. In our next post, we will explore specific strategies to mitigate metabolic adaptation and support long-term weight management success.


Dr. Cardona is board certified in family medicine and obesity medicine and is the founder and physician owner of Cardona Direct Primary Care and RefineMD Aesthetics. Currently accepting new patients. (904) 551-4625. Visit for information on our obesity management services.

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