We all know the person who seems to be able to eat whatever they want and maintain weight, while we also know the person who even looks at food and gains weight. Energy balance dictates whether an individual gains or loses weight – if you eat more calories than you expend, you gain weight and if you eat fewer calories than you expend, you lose weight.
Total Daily Energy Expenditure (TDEE) is colloquially referred to as the “metabolism”; people with a large TDEE are said to have “fast metabolisms”. People with a relatively low TDEE are said to have “slow metabolisms”.
In this article, I will be going over the components of your metabolism, specifically focusing on adaptive thermogenesis.
What is Metabolism?
The metabolism, also referred to as TDEE in this article, is made up of two components:
resting energy expenditure and non-resting energy expenditure. Resting energy expenditure is usually interchangeable with Basal Metabolic Rate (BMR).
Non-Resting Energy Expenditure (NREE) is made up of Exercise Energy Expenditure, Thermic Effect of Food (TEF) and Non-Exercise Activity Thermogenesis (NEAT).
1] Basal Metabolic Rate
BMR is the amount of energy that is required by vital processes in the body. To put it simply, it is the energy that is required to simply live while lying down, inactive in a relaxed and thermoneutral state. BMR has a variation of 10-15% (McMurray et al., 2014).
As an example, if the average individual of a certain height, weight, and body composition has a BMR of 2,000kcal then there is going to be a total variance of 300kcal. Thus, there will be individuals that have a BMR of 1,750kcal and others with a BMR of 2,150kcal. It is important to note that this is NOT their total daily energy expenditure; we are still only discussing BMR.
By looking at these numbers, we can see that BMR alone is likely not enough to explain why Alberto Nunez can maintain weight eating 3,500kcal per day or more while someone of that similar weight and body composition would “dirty bulk” on the same intake.
2] Thermic Effect of Food
The Thermic Effect of Food (TEF), also known as Diet-Induced Thermogenesis, is the energy that is expended to digest food. It includes the energy required for the intestinal absorption of the nutrients, the initial metabolism of the nutrient as well as their immediate storage. TEF makes up approximately 10% of TDEE. While the TEF of protein, carbs and fats in isolation differ, the TEF for a mixed meal is 10% (Westertrep et al., 2004).
TEF does not seem to have large variability unless weight is altered. It seems that a 10% weight loss can decrease TEF, but it may not significantly decrease after that (Leibel et al., 1995). Further, overweight insulin-resistant individuals may also have a lower TEF. (Donahoo et al., 2004). However, in healthy, non-obese individuals TEF is relatively stable at approximately 10% of TDEE.
3] Exercise Energy Expenditure
Exercise energy expenditure simply is the energy expended during volitional exercise activity; this includes sport and fitness related activity
4] Non-Exercise Activity Thermogenesis
Non-Exercise Activity Thermogenesis, also known as NEAT is the energy expended performing movements that are not considered volitional activity. These movements include daily living, fidgeting, rearranging posture, hand-gestures, etc.
For more on NEAT, go check out THIS in which you’ll find bits James Krieger’s presentation on NEAT.
Metabolic rate is dynamic and may change in response to diet, body fat levels, hormones and other factors. The dynamic nature of metabolism makes sense; as you would not want to maintain a “fast” metabolism during a period of starvation. Your body’s main priority is not to get an OCB Pro-Card, or to look shredded at the beach, it is to survive. Thus, in periods of caloric deficit and subsequent weight loss, there will be a decrease in metabolic rate.
One cause of a lower TDEE is that you simply have a smaller, lighter body to move and this requires less energy. In a similar manner, when you gain weight your TDEE will increase because you have a larger body to move and this requires more energy.
However, there seems to be a change in metabolic rate that is independent of changes in body weight and body composition (Muller et al., 2016). When losing weight, adaptive thermogenesis might cause a decrease in metabolic rate that exceeds what can be accounted for due to having a smaller body. When gaining weight, adaptive thermogenesis might cause an increase in metabolic rate that exceeds what can be accounted for due to having a larger body.
Weight Loss and Adaptive Thermogenesis
1] Mechanical Model: In the mechanical model, the reduction in energy expenditure is directly in response to having a smaller body to move.
2] Threshold Model: In this model, energy expenditure will decrease beyond what can be accounted for by body weight loss until a certain limit is met. The limit is thought to be the lowest end of the individual’s body fat set-point. Once that set point is reached, the only further loss of energy expenditure will be due to having a smaller body
3] Spring Model: In the spring model, energy expenditure continuously decreases in proportion to the amount of weight that is lost. Thus, the more weight you lose, the greater the drop in adaptive thermogenesis
Figure 2. Models of adaptive thermogenesis. Adapted from Rosenbaum & Leibel (2016).Figure 2. demonstrates three ways to model adaptive thermogenesis in response to weight loss (Rosenbaum & Leibel, 2016).
A study by Rosenbaum and Leibel (2016) looked at which of these models occurs during weight loss. In this study, the researchers measured TDEE, NREE and BMR.
In this study, 18 subjects were placed in a caloric deficit to lose 10% of their weight at the start of the study (Wt-initial). Once the new body weight (Wt-10%) was achieved, it was maintained for a few weeks and then subjects were placed under caloric deficit to achieve a 20% body weight loss from their starting weight (Wt-20%). TDEE, NREE and BMR were measured at Wt-initial, Wt-10% and Wt-20%. The researchers found that BMR followed the threshold model; BMR dropped significantly when the subjects went from Wt-initial to Wt-10%. However, BMR was not significantly different when subjects went from Wt-10% to Wt-20%. Thus, BMR follows a threshold model – it dropped to a certain point and then did not drop further.
Interestingly, NEAT responded differently. The researchers observed that NEAT dropped significantly when subjects went from Wt-initial to Wt-10% and dropped even more when the subjects went from Wt-10% to Wt-20%. Based on this, it seems that NEAT follows the spring-loading mode, meaning that NEAT decreases in proportion to the amount of weight loss.
Weight Gain and Adaptive Thermogenesis
As an individual gains weight, their body will become larger, heavier and more energy-expensive to move. The result will be an increase in energy expenditure. However, there can also be an increase in energy that is greater than would be expected based on the individual’s body weight and composition.
In a study by Levine et al. (1999), 16 non-obese adults were fed 1,000kcal/d over their “maintenance intake” for 8 weeks. The mean weight gain was 10.34lbs. However, the mean gain is not the interesting part of this study. The interesting part is the range of fat gain; the subjects gained between 0.792lbs to 9.31lbs – more than a tenfold difference. The overfeeding was supervised, making it hard to blame the results on lack of adherence to the diet.
Well then, what happened?
The researchers measured BMR and found that it increased by an average of 5%, meaning that it couldn’t have accounted for the variability in fat gain. TEF increased, but it was proportional to the increase in food. The more food you eat, the more energy you expend overeating it. However, the increase in TEF also did not account for the variability in fat gain.
Luckily, the researchers also measured NEAT. It is important to note that NEAT is difficult to measure as it’s hard to define the line between formal exercise and NEAT. To measure NEAT, Levine and colleagues kept the subject’s exercise constant. Thus, if there was an increase in NREE, which is Exercise Energy Expenditure + NEAT then the increase must have come from NEAT, since exercise was kept constant.
Figure 3. Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Levine et al., (1999).
It was found that the average increase in NEAT was +336kcal/d and could account for two-thirds of the mean increase in energy expenditure in response to overfeeding. Again, the interesting part about this study is the variability in responses. There was a range of -98 to +692kcal/day, meaning one individual actually decreased NEAT while one increased it by almost 700kcal per day. The change in NEAT was found to be correlated to the amount of fat gain in the subjects (correlation coefficient 5 0.77, probability , 0.001). Figure 3. demonstrates how the individuals that had the smallest, or even a negative change in NEAT experienced the greatest fat gain. Meanwhile, the individuals that had the biggest increases in NEAT experienced the least amount of fat gain.
Can I Fidget My Way Up to Endless Calories?
Naturally, the question that will follow is can you consciously increase your NEAT in an effort to eat more calories while still reaching your physique goals? Whether to cut, bulk or maintain, we tend to want to eat more food. We want to either diet with higher calories, eat more during a bulk without gaining too much fat and maintain weight while still enjoying all the macros.
Unfortunately, NEAT is hard to consciously maintain or increase due to the nature of the movements – they are the ones that you typically don’t think about. It’s difficult to become a fidgety person if you’re typically the person that basically lies down on their seat or to get into the habit of tapping your feet, bobbing your head to music, moving your hands when you talk, etc.
For this reason, most people attempt to maintain a certain level of adaptive thermogenesis by tracking their step-count using a pedometer. It is becoming increasingly common to pursue at least 10,000 steps per day. However, recent literature shows that there may be an upper limit to how much TDEE can be increased by increasing physical activity.
An interesting study by Pontzer et al., (2012) looked at the energy expenditure of the Hadza population – one of the last hunter-gatherer populations in the world. The Hadza have no modern transportation, livestock or firearms. They rely on walking and performing physically-demanding tasks in order to survive.
Pontzer and colleagues recruited 30 Hadza adults to monitor their physical activity and total daily energy expenditure and compared it to values from Western populations. The researchers measured TDEE using Doubly Labelled Water. They also measured the cost of transport by measuring energy expenditure while wearing portable respiratory system that analyzed CO2 production and O2 consumption. Further, the Hadza volunteer’s daily activity was measured by equipping the volunteers with GPS devices.
Shockingly, the TDEE of Hadza adults was found to be similar to those in Western populations. However, the Hadza population had a significantly greater estimated Physical Activity Level than their Western counterparts. These data support a constrained TDEE model, meaning that the body adapts to maintain TDEE within a certain range.
Pontzer and colleagues suggested that the individuals in the Hadza population that walk the most may compensate for their large physical activity levels by decreasing energy expenditure in other areas. These individuals may lay down instead of sitting or by performing fewer chores outside of the ones that demand travelling by foot (Pontzer et al., 2015).
Further, these data suggest that Hadza adults have a lower BMR than Western population, which may be another way in which their TDEE is lowered (Pontzer et al., 2012)
The literature on the Hadza population suggests that there may be an upper limit to an individual’s TDEE, regardless of physical activity. It is likely that a short-term increase in physical energy expenditure such as performing cardio or adding in steps for a diet will lead to an acute increase in TDEE. However, it’s plausible that if the additional physical activity is maintained for a long period of time then the body may adapt to it by lowering energy expenditure in other areas.
It is likely that the threshold model applies to BMR but not NEAT because of the nature of BMR – it is the energy required for essential processes in the body. There is a limited amount of BMR that can be reduced while still maintaining proper bodily function. However, NEAT can continuously decrease make your body more energy efficient and decrease your TDEE as the caloric deficit becomes more severe for a prolonged period of time.
It may be a good idea to use a pedometer and make an effort to observe your regular fidgeting behaviour prior to starting a diet. During the diet, you can attempt to maintain your usual step count to mitigate subconscious decreases in step count. Further, if you were previously a highly fidgety person but now you can’t bring yourself to tap your feet to your favourite rock song then you might benefit from slightly increasing your step count to account for losses in NEAT. Increasing your step-count and accounting for a loss of spontaneous movement may work in this scenario because a diet is relatively short-lived.
While you will likely not be able to completely negate the decrease in NEAT and the effects of adaptive thermogenesis on “slowing” your metabolism, you might be able to reduce them.
Weight Gain and Maintenance
The majority of your athletic career and life should be spent in periods of caloric maintenance or surplus. Thus, it’s important to give practical applications during this time instead of simply focusing on weight loss.
As demonstrated by the studies on the Hadza population, long-term increases in activity may decrease energy expenditure in other areas of life and there may be an upper limit to an individual’s TDEE. As a result, it is unlikely that you will be able to significantly increase TDEE by making conscious efforts to control adaptive thermogenesis.
Levine et al., (1999) demonstrated that overfeeding results in a wide range of responses in NEAT. However, the researchers in this study did not instruct the individuals being overfed to attempt to move more in response to the calories – the change in NEAT was the individual’s natural response.
When in a period of calorie surplus or maintenance, it’s a good idea to let your NEAT fall where it may. If you truly feel energized and want to go for a walk, find yourself tapping your feet more, dancing to music or taking the stairs more often then great! You may be someone who naturally increases energy expenditure in response to the additional calories.
If you are someone who does not naturally increase energy expenditure in response to additional calories then attempting to walk for hours or become fidgety in an effort to eat more food will likely not yield the results you are seeking.
Finally, attempting to bring up levels of NEAT during periods of surplus or maintenance presents an additional psychological stressor that is likely unnecessary. It is a good idea to minimize the mental stressors in a period of non-dieting to conserve that mental-stamina for periods of dieting.
Metabolism and Adaptive Thermogenesis
The human metabolism is made up of your Basal Metabolic Rate, Thermic Effect of Food, Exercise Energy Expenditure and Non-Exercise Activity Thermogenesis.
- BMR is the energy that is required to stay alive while laying down, in a thermoneutral environment while in a relaxed state.
- TEF is the energy that is required to digest food and absorb the nutrients found in that food.
- Exercise Energy Expenditure is the energy expended while performing an exercise.
- Non-Exercise Activity Thermogenesis is the energy expended during non-volitional activity such as fidgeting, rearranging posture, doing hand gestures while talking, tapping your head to music, etc.
These four components determine how much energy you will expend per day.
Total body weight has a large influence on Total Daily Energy Expenditure, as a larger body is more energy-demanding to move while a smaller body is less demanding. When you lose weight, total daily energy expenditure decreases due to a loss of body mass; similarly, when you gain weight total daily energy expenditure increases due to a gain in body mass. However, there seems to be a change in total daily energy expenditure that exceeds what could be predicted by the loss or gain of body mass – this is referred to as adaptive thermogenesis. Adaptive thermogenesis usually decreases or increases energy expenditure by altering daily steps, fidgeting and other spontaneous movements, among many other ways.
While you can track your steps and make choices that will cause you to expend more energy throughout the day, there is an upper limit to how much you can benefit from this; both mentally and physically. While you can control some parts of your adaptive metabolism such as how many steps you take in a day, the type of transportation you use, or if use a stand-up desk, to name a few.
There are other parts of your adaptive metabolism that you cannot control such as mitochondrial efficiency, how much you fidget or how often you rearrange your poster. These factors cannot be controlled for a few reasons; one of which is that it seems there is an upper-end to how much energy each individual can expend in one day. It seems that if an individual reaches this upper-end by performing certain activities, they might significantly decrease their energy expenditure in other activities to “make-up” for that expended energy.
Further, due to the subconscious nature of NEAT, it would be too difficult to monitor how much fidgeting is done in an average day and then attempt to replicate or even increase it on a regular basis. Finally, physique-sport is already psychologically taxing; it requires nutrition considerations, hard training, constant protein feedings, proper sleep, recovery and other habits. It would be a significant mental burden to make a conscious effort to tap your feet, fidget, rearrange posture and perform other movements that are usually done subconsciously. Remember that physique-sport is a part of your life, but should not be your entire life.
Control what you can, to a reasonable degree.
Miguel is an athlete, academic and coach with a burning passion for science and fitness. He is studying Nutritional Biochemistry at McGill University, Canada, and has the goal of obtaining a Ph.D. in Exercise Science. Miguel’s purpose for obtaining an extensive education is to become the best coach possible and to contribute to the academic field by performing research on strength and physique athletes.
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Levine, J. A., Eberhardt, N. L., & Jensen, M. D. (January 01, 1999). Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science (New York, N.y.), 283, 5399, 212-4.
Leibel R.L., Rosenbaum M., & Hirsch J. (1995) Changes in Energy Expenditure Resulting from Altered Body Weight. N Engl J Med 1995; 332:621-628
McMurray, R. G., Soares, J., Caspersen, C. J., & McCurdy, T. (2014). Examining Variations of Resting Metabolic Rate of Adults: A Public Health Perspective. Medicine and Science in Sports and Exercise, 46(7), 1352–1358.
Pontzer, H., Raichlen, D. A., Wood, B. M., Mabulla, A. Z. P., Racette, S. B., & Marlowe, F. W. (2012). Hunter-Gatherer Energetics and Human Obesity. PLoS ONE, 7(7), e40503. http://doi.org/10.1371/journal.pone.0040503
Pontzer, H., Raichlen, D. A., Wood, B. M., Emery, T. M., Racette, S. B., Mabulla, A. Z., & Marlowe, F. W. (January 01, 2015). Energy expenditure and activity among Hadza hunter-gatherers. American Journal of Human Biology : the Official Journal of the Human Biology Council, 27, 5.)
Rosenbaum, M., & Leibel, R. L. (2016). Models of energy homeostasis in response to maintenance of reduced body weight. Obesity (Silver Spring, Md.), 24(8), 1620–1629. http://doi.org/10.1002/oby.21559
Trexler, E. T., Smith-Ryan, A. E., & Norton, L. E. (2014). Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition, 11, 7. http://doi.org/10.1186/1550-2783-11-7
Westerterp, K. R. (2004). Diet induced thermogenesis. Nutrition & Metabolism, 1, 5. http://doi.org/10.1186/1743-7075-1-5
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