What is energy balance?

How does energy balance relate to dieting?

What is metabolism?

What is metabolic adaptation?

Why does it happen?

How do I fix it?

“Weight loss isn’t the goal, sustaining weight loss is the goal”

Energy Balance

The first law of thermodynamics also known as the Law of Conservation of Energy, states that energy cannot be created nor destroyed; energy can only be transferred or changed from one form to another [1]. Because of this law, in regard to bioenergetics, energy and calories are interchangeable so for the purpose of this article, I will be referring to both.

Now let’s get started…

Before understanding metabolic adaptation, a widely used concept of energy balance must be understood as it is the prime determinant of weight loss, maintenance, and gain. Energy balance is the difference from the number of calories consumed and energy expended in order to maintain basic metabolic and physiological functions. Weight loss, maintenance, and gain all come down to the simple scientifically proven concept of calories in vs. calories out (CICO). For example, if an individual is in a calorie deficit, meaning they are consuming less calories than expending, then they are in a negative energy balance, therefor losing weight. If an individual is in a calorie surplus, meaning they are consuming more calories than expending, then they are in a positive energy balance, therefor gaining weight. This energy balance equation remains undisputed for explaining changes in an individual’s body weight [2]. Simple right?

Tracking ‘calories in’ AKA total daily energy intake (TDEI) is a very concrete facet of CICO but tracking ‘calories out’ AKA total daily energy expenditure (TDEE) is a I little bit more complex. TDEE contains four very important components including basal or resting energy expenditure (basal EE), thermic effect of feeding (TEF), exercise activity thermogenesis (EAT), and non-exercise activity thermogenesis (NEAT). All four of these components must be accounted for when determining TDEE.

TDEE: Total daily energy expenditure is the total amount of calories expended during a 24-hour period. TDEE = Basal EE + TEF + EAT + NEAT.

Basal EE: Basal energy expenditure is the largest component to TDEE as its average contribution is estimated to be around 70% of TDEE [3]. Basal EE refers to basal metabolic rate (BMR), which is the minimal amount of energy needed to sustain basic bodily functions. To put it into perspective, if you were at complete rest and did not eat or drink for a 24-hour time period, you would expend around 70% of your energy. Basal EE/BMR varies for everyone depending on their age, height, sex, genetics, and lean body mass. The average basal EE for males falls within the range of 1,580–1,870 whereas the average basal EE for females falls within the range of 1,150–1,440 [4]. To get a more accurate measurement, basal EE can be measured in three different ways including a well-controlled laboratory test of direct or indirect calorimetry and the Mifflin-St. Jeor equation. Direct calorimetry is the gold standard means of measuring human metabolic rate and its use has been fundamental for understanding metabolism in health and disease. Direct calorimetry provides the user with the unique capacity to quantify the heat produced from aerobic and anaerobic metabolism by measuring heat exchange between the body and the environment [5]. Indirect calorimetry is now more common; it measures the respiratory gas exchange of oxygen consumption (VO2) and carbon dioxide production (VCO2) during exercise. Aside from the laboratory tests, the Mifflin-St. Jeor equation is used to estimate Basal EE. Basal EE for females = (10 x body weight in kilograms) + (6.25 x height in centimeters) — (5 x age) — 161. Basal EE for males = (10 x body weight in kilograms) + (6.25 x height in centimeters) — (5 x age) + 5 [4].

TEF: The thermic effect of feeding refers to the energy expended during ingestion, digestion, and storage of food and fluid; its average contribution to TDEE is estimated to be around 10%. However, it should be noted that different macronutrients as well as other variables (size of meals, processing of foods, duration) contribute separately to this effect [6]. TDEI as mentioned before is a very concrete facet of CICO and is determined by the sum of calories from protein, carbohydrates, and fats. Note that for every 1 gram of protein = 4 calories, 1 gram of carbohydrates = 4 calories, and 1 gram of fat = 9 calories. TEF = TDEI x 0.10.

NEAT: Non-exercise adaptive thermogenesis refers to the energy expended during non-exercise/involuntary tasks such as but not limited to typing, walking, and cooking, and its average contribution to TDEE is estimated to be around 20% of basal EE. All TDEE contributors are subjected to some degree of both inter and within-individual variability depending on fitness level and calories consumed [7], where large variations in TDEE are dictated by changes in NEAT. For example, NEAT could contribute to 15% of TDEE in sedentary individuals and 50% or more in active individuals [8]. For an average estimation of NEAT, use the following equation: NEAT = basal EE x 0.20.

EAT: Exercise activity thermogenesis refers to the energy expended during intentional exercise and its average contribution to TDEE is estimated to be around 5–10%. Similarly to NEAT, large variations in TDEE are dictated by EAT. These variations are dependent on the type of exercise, intensity of exercise determined by heart rate in comparison to heart rate max, fitness level (sedentary, average, anaerobic athlete, aerobic athlete), body weight, and sex.

Energy Balance in its Relation to Dieting

Despite what you have heard or what you may think in regard to different fad diets, the ONLY way they work for individuals who want to lose body weight from fat is if they are in a negative energy balance. For example, the Ketogenic diet consists of a low carbohydrate and high fat and protein diet. If the individual is not in a negative energy balance, the reduction of carbohydrates won’t result in body weight loss from fat.

“But how have I lost 10 pounds in 2 weeks from the Ketogenic diet?” The answer to this is simple but understanding the more complex explanation to this question will result in a better grasp of the answer. So here we go…. After carbohydrates have been ingested and broken down into glucose (the main source of ATP production/energy) by the small intestine, it either undergoes glycolysis (used for energy), glycogenesis (stored as glycogen in the skeletal muscles or liver), or lipogenesis (converted to fat). When glycogenesis occurs, glucose is stored as glycogen in the liver to regulate and manage blood glucose. Glucose is also stored in skeletal muscles as glycogen, waiting for its que (exercise) to undergo glycolysis (production of energy). So how does the Ketogenic diet and weight loss come into play here? Glycogen molecules contain water, therefore, the more stored glycogen in your skeletal muscles, the more water you retain. Consuming very little carbohydrates results in a depletion of glycogen stores and water, which is the explanation as to why so much weight was lost in 2 weeks of following the Ketogenic diet. Unfortunately, the scale doesn’t tell you whether the weight that you lost was fat or water, but in this case unless you were in a negative energy balance, it was 100% water. I mean, wouldn’t you rather lose weight from fat AND eat carbohydrates than just lose weight from water, possibly even gain fat, and limit your carbohydrates? For the many people out there who have lost weight from fat while on fad diets shouldn’t give the credit to the diet, instead, give it to CICO.

In summary, although I definitely don’t recommend doing this, CICO basically means that you can consume all your calories from potato chips and if you are in a negative energy balance, you WILL lose weight from fat over time.


Energy balance and CICO are both very simple concepts, but the physiological variables that are involved, that a lot of people don’t account for, has created very misleading perceptions. Unfortunately, these perceptions have resulted in loss of credibility of this scientifically proven concept of CICO.

The human body is a very complex bioenergetic system in which it undergoes many metabolic pathways in order to maintain homeostasis. Homeostasis is an important dynamic and fundamental concept in physiology and is defined as the ability of the body to maintain relatively stable internal conditions through slight modifications via the endocrine system which releases hormones and the neurological system which releases neurotransmitters. Slight modifications include but are not limited to temperature, pH level, blood glucose, and blood pressure. All bodily functions and systems contribute to maintaining homeostasis and this process is constantly occurring. Think about your body as an efficient machine that can self-regulate in order to continue living. For example, in a hyperglycemic state (high blood glucose levels), the pancreas releases insulin, which promotes the uptake and storage of glucose; this results in a decrease in blood glucose levels to reach a homeostatic state. Pretty amazing if you ask me. Metabolism is a key factor in maintaining homeostasis. It is a combination of two processes: anabolism and catabolism. Anabolic pathways require energy to generate complex macromolecules such as lipids and nucleotides via anabolic hormones, whereas the catabolic pathway breaks molecules down to produce energy [9].

Metabolic Adaptation

“The great irony of weight loss is that our modern problems were our ancient saviors” [10]

Because we began as primitive beings, metabolic adaptation AKA adaptive thermogenesis allowed us to conserve as much energy as possible to maintain homeostasis for our survival (remember that hunting and gathering was necessary and primarily relied on for survival). The storage of fat allowed us to survive during uncertain times of famine and hunger. Now that we are no longer living in a primitive time and food is widely accessible, the unwanted storage of fat has become our modern problem. For a simple comparison, think about your body as a car and your fat stores as gas. If you have a full tank of gas, meaning that you have a large amount of fat stores, you DON’T want an energy efficient car because that would take a longer period of time to deplete your gas tank as opposed to an energy inefficient car. Having an energy efficient car when gas is inaccessible would be ideal, but in a society where food is very accessible, having energy efficient cars is our downfall. So, whether we like it or not, adaptive thermogenesis has always been part of our physiology and given that basal EE/BMR predominantly contributes to the majority of TDEE, it is the factor of CICO that drives energy balance i.e. weight loss, maintenance, and gain. Adaptive thermogenesis is our bodies response to a calorie deficit or surplus by either decreasing or increasing TDEE. The severity of the adaptations depends on the duration of the calorie deficit or surplus period, where longer duration will increase the adaptions [11]. When we are in a calorie restriction, our cars become more and more efficient, which is what we want to avoid. In other words, these adaptations should ideally be limited for sustained weight loss.

Extreme calorie deficit effect on hormones: As mentioned before, the neurological system is responsible for detecting and responding to changes/disrupters in homeostasis and works with the endocrine system which is responsible for releasing hormones to regulate homeostasis. For example, during periods of rapid or extreme calorie deficits, the “stress hormone” cortisol is released by the adrenal cortex. Cortisol is activated to maintain blood glucose levels as our central nervous system (CNS) AKA brain needs an uninterrupted flow of glucose to properly function. Cortisol does this by decreasing leptin (a hormone that is responsible for controlling appetite and regulating metabolism), increasing proteolysis (the breakdown of proteins into amino acids for energy) and stimulating gluconeogenesis (converting amino acids, lactates, ketones, and oxaloacetates into glucose for our CNS). These are all responses that we DON’T want, as a decrease in leptin facilities a decrease in thyroid hormone, decrease in sex hormones, decrease in NEAT and TDEE, increase in hunger hormones, and an increase in body fat [10].

Extreme calorie deficit effect on NEAT: Being in a calorie deficit will result in a decrease of TDEE as it is our bodies protective mechanism to conserve energy so that we don’t starve. As stated before, NEAT is a component of TDEE that can vary to a great extent depending on calories consumed. In a study on overweight females it was concluded that NEAT was reduced 27% for females in a calorie deficit totaling to 800 calories a day. In a separate study on 12 males and 4 females, it was concluded that NEAT increased up to 69% for subjects in a calorie surplus of 1,000 calories above maintenance [12]. Practically speaking, if you are in a calorie deficit, your bodies protective mechanism of conserving energy will result in a decrease in NEAT such as fidgeting, walking, and even blinking.

Extreme calorie deficit effect on BMR: Adaptive thermogenesis is not just limited to NEAT. BMR is also a component that is compromised from adaptive thermogenesis by decreasing to conserve energy. A meta‐analysis of a cross‐sectional study found that subjects who had lost weight exhibited a 3% to 5% lower BMR compared with control subjects who had not lost weight [11]. The reality about adaptive thermogenesis is that is not just a drop in metabolic rate or BMR, but rather, a multifaceted set of adaptions that involves regulation of energy expenditure, appetite, reproduction function, and the balance between anabolism and catabolism [10]. Having a “fast” metabolism is what most dieters wish they had, and it is unfortunate that without even knowing, they are “slowing” down their metabolism by dieting in unhealthy and unsustainable ways.

Extreme calorie deficit effect on overshooting: The epic failure of diets is well documented as body fat regain AKA overshooting is very common. Increasing calories at a fast rate after being in a calorie restriction for a long period of time won’t allow your metabolism to adjust and adapt to its “new normal”, which is why excessive weight gain occurs. 6 out of every 7 people who are overweight or obese will lose a significant amount of weight in their lifetime, but 95% of them will regain all the weight they lost within 3 years. Of those, 1/3–2/3 will regain more weight than they lost [13]. Technically speaking, based on these statistics and the premise that a successful diet means sustained weight loss, then diets really only work 5% of the time. The over 80% recidivism rate to pre-weight loss levels of body fatness after otherwise successful weight loss is due to the coordinate actions of metabolic, behavioral, neuroendocrine, and autonomic responses designed to maintain body energy stores (fat). This ‘adaptive thermogenesis’ creates the ideal situation for weight regain and is operant in both lean and obese individuals attempting to sustain reduced body weights. Much of this opposition to sustained weight loss is mediated by the adipocyte-derived hormone ‘leptin’ [14]. As mentioned before, leptin is a hormone that is responsible for controlling and regulating our appetite. Leptin levels decrease as individuals lose weight and increase to excessive levels as weight is restored, which is a common factor to overshooting [15].

Mitigating the Effects of Metabolic Adaptation and Strategies to Restore Metabolism

Let’s discuss weight loss…

Being in a calorie deficit inevitably results in metabolic adaptation but the effects of metabolic adaptation can be controlled and mitigated. Without guidance, extreme calorie-restrictive diets are often utilized to reduce body weight. The issue with this is that, because our metabolisms are so adaptive, a large decrease in excessive amounts of calories over a long period of time will result in hitting a plateau and losing body weight at a much slower rate. CICO is still very true in the sense that although an individual is consuming less and less calories, their metabolism has adapted so much that ‘calories out’ is also decreasing tremendously. Many dieters don’t understand this and unfortunately think the answer to overcoming their plateau and losing more weight is to continue decreasing their calorie intake and/or increasing their energy expenditure. This can be very dangerous and cause a disrupter in homeostasis, which may cause fatigue, loss of strength, increase in injuries, poor ability to recover, dizziness, headaches, mood swings etc., due to a low-calorie intake.

Stay educated: Oftentimes in the fitness industry, rapid weight loss is glorified and used as a ploy to increase revenue on coaching services or special dieting strategies. For the “coaches” out there who recommend rapid weight loss dieting strategies by constantly increasing cardio and/or decreasing calorie intake for their clients are behaving unethically and are either coaching just for income or are unaware of their wrongdoings. It is unfortunate that so many individuals fall into the rapid weight loss scheme, but the effects of metabolic adaptation can easily be mitigated by staying educated.

No more yo-yo diets: Weight cycling or yo-yo dieting is a common term that describes the repetitive process in which an individual successfully loses weight but is unsuccessful at maintaining weight loss resulting in weight gain and therefor tries to lose weight again. Weight cycling and yo-yo dieting are not limited to the obese or overweight; 50% of the population with normal weight yo-yo diet [16]. The fact is that rapid weight loss and drastic calorie deficits don’t yield sustainable weight loss. 1 to 2 pounds of weight loss per week is a healthy and sustainable goal and people who lose weight gradually and steadily are more successful at keeping weight off. Remember, healthy weight loss isn’t just about a “diet” or “program”, it’s about an ongoing lifestyle that includes long-term changes in daily eating and exercise habits [17]. If you can’t see yourself sustaining your diet not only until you reach your goal, but for the rest of your life, then it is likely that it won’t work.

Diet breaks: Taking a break from dieting and eating at maintenance calories (remember that in terms of CICO, calories in = calories out results in energy maintenance) is the process in which many take to undergo a diet break. The common length for undergoing diet breaks are between 1–2 weeks and countless of studies have proven that doing this results in benefits regarding sustained weight loss and adaptive thermogenesis. In a very thorough research study on diet breaks, two groups of participants followed a 16-week calorie restriction diet where one group maintained the diet throughout the whole 16 weeks (control group) and the other group underwent a diet break by eating at maintenance calories every 2 weeks for a total of 30 weeks to ensure 16 weeks of dieting (dieting group). Based on the results from the study, the dieting group lost 47% more weight than the control group. Although both groups regained weight 6 months following the study, the diet group maintained an average weight loss of 8kg more than the control group [18]. Aside from the physiological benefits of diet breaks, they can be utilized for psychological benefits as well, as it allows the individual to be more flexible with their calorie intake. Despite the name “diet break”, the individual should still be practicing ideal dietary behaviors of eating sufficient micronutrients, fiber, and protein. Diet breaks can be implemented in many different ways and the frequency and length of them depend on the individual.

Reverse dieting: Reverse dieting is a strategy in which an individual gradually increases their calorie intake following a calorie deficit in order to restore metabolism and minimize weight gain. When an individual is at their metabolic floor, meaning they are consuming a very low-calorie diet and have hit a plateau with their body weight, it is in their best interest to undergo a reverse diet. To avoid overshooting while restoring one’s metabolism, this process should happen very slowly. Just like diet breaks, reverse dieting can be implemented in many different ways and the results in regard to body fat, lean body mass, and weight gain differ amongst individuals. For example, within 20 weeks, individual A might hyper respond to a reverse diet by losing 8–10 pounds of bodyweight while at a 50% calorie increase whereas individual B might gain 8–10 pounds of body weight while at a 50% calorie increase. For this reason, it is best to follow guidance from a credible and experienced coach as it might be difficult to self-program the most ideal reverse dieting protocol. An example of a protocol for reverse dieting just in terms of energy intake is an initial calorie increase of about 10–15% during the first week of reverse dieting and a 2–5% calorie increase for every 1–2 weeks following. The length of the reverse dieting phase is very dependent on the individual and their previous dieting history. Generally speaking, the longer the individual was at an extreme calorie deficit, the longer their reverse dieting phase should be. Of course, because weight gain is a concern during reverse dieting, it should still be considered as the reverse dieter might better adhere to the protocols. It should be noted that the sacrifice of a little weight gain is worth the metabolic adaptations to increased calorie intake.

My Stance and Personal Experience on Metabolic Adaptation

If you don’t know already, I have gone through two intentional weight gain phases and two intentional weight loss phases. During my recent weight gain phase, I gained a total of 15.5 pounds within 6 months in hopes of gaining strength, muscle mass, and most importantly, restoring my metabolism. I did this by hiring a coach and following a macro-based diet that consisted of 50% carbohydrates, 30% protein, and 20% fat. The first image is of me during the first week and the second image is of me 5 months into my intentional weight gain. I knew that I was going to gain fat along with muscle mass, but I was okay with doing so as I knew it would be worth it. After maintaining my weight for a few months following my weight gain, I decided to begin a slow and steady weight loss phase. I am currently doing this by following a flexible diet and have been able to lose 10 pounds since the final week of my weight gain. I am so glad that I made the decision to gain weight for 6 months as I am now able to lose weight in a more sustainable way while still eating a relatively large number of calories. Through this process I learned that we shouldn’t expend calories so that we can consume them, instead, we should consume calories so that we can expend them. Having more energy and better sleep as well as expending more calories throughout the day is well worth the weight gain. For those of you who are at your metabolic floor, I understand that you don’t want to regress in terms of gaining weight, but it is necessary for a healthy and sustainable lifestyle. Long-term gratification is so much more rewarding than short-term and short-lived gratification. Be patient and trust science.


[1] Zohuri, B., & Mcdaniel, P. (2018). First Law of Thermodynamics. Thermodynamics in Nuclear Power Plant Systems, 99–148. doi:10.1007/978–3–319–93919–3_5

[2] Martinex-Gomez, M. G. (2020, June 14). Metabolic Adaptation to Weight Loss: A Brief Review [Scholarly project]. In Research Gate. Retrieved September 29, 2020, from https://www.researchgate.net/profile/Mario_Garcia_Martinez-Gomez/publication/342155373_Metabolic_Adaptation_to_Weight_Loss_a_Brief_Review/links/5ee56d9892851ce9e7e37ef5/Metabolic-Adaptation-to-Weight-Loss-a-Brief-Review.pdf

[3] Levine, J. (2005). Measurement of energy expenditure. Public Health Nutrition, 8(7a), 1123–1132. doi:10.1079/PHN2005800

[4] Lloyd, L. K., & Patek, K. T. (2017). A Laboratory Textbook of Exercise Physiology (32nd ed.). Stipes Publishing Co.

[5] Kenny, G. P., Notley, S. R., & Gagnon, D. (2017). Direct calorimetry: a brief historical review of its use in the study of human metabolism and thermoregulation. European journal of applied physiology, 117(9), 1765–1785.

[6] Calcagno, M., Kahleova, H., Alwarith, J., Burgess, N. N., Flores, R. A., Busta, M. L., & Barnard, N. D. (2019). The Thermic Effect of Food: A Review. Journal of the American College of Nutrition, 38(6), 547–551. https://doi.org/10.1080/07315724.2018.1552544

[7] Donahoo, W. T., Levine, J. A., & Melanson, E. L. (2004). Variability in energy expenditure and its components. Current opinion in clinical nutrition and metabolic care, 7(6), 599–605. https://doi.org/10.1097/00075197-200411000-00003

[8] Levine J. A., Eberhardt N. L., Jensen M. D. (1999). Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science (80- ).

[9] Schwartsburd P. M. (2017). Catabolic and anabolic faces of insulin resistance and their disorders: a new insight into circadian control of metabolic disorders leading to diabetes. Future science OA, 3(3), FSO201. https://doi.org/10.4155/fsoa-2017-0015

[10] Trexler, E. (2019, March 26). The Metabolic Adaptation Manual: Problems, Solutions, & Life After Dieting. https://www.strongerbyscience.com/metabolic-adaptation/.

[11] Astrup, A., Gøtzsche, P. C., Werken, K. V., Ranneries, C., Toubro, S., Raben, A., & Buemann, B. (1999). Meta-analysis of resting metabolic rate in formerly obese subjects. The American Journal of Clinical Nutrition, 69(6), 1117–1122. doi:10.1093/ajcn/69.6.1117

[12] Hunter GR, Fisher G, Neumeier WH, Carter SJ, Plaisance EP. Exercise Training and Energy Expenditure following Weight Loss. Med Sci Sports Exerc. 2015 Sep;47(9):1950–7. doi: 10.1249/MSS.0000000000000622. PMID: 25606816; PMCID: PMC4508245.

[13] Norton, L. (Director). (2018, September 21). Why Diets Fail — The Body’s Self Defense System [Video file]. Retrieved October 22, 2020, from https://www.youtube.com/watch?v=_uok8Itwles

[14] Rosenbaum, M., & Leibel, R. L. (2010). Adaptive thermogenesis in humans. International journal of obesity (2005), 34 Suppl 1(0 1), S47–S55. https://doi.org/10.1038/ijo.2010.184

[15] Sigel, E. (2009). DISORDERED EATING BEHAVIORS: ANOREXIA NERVOSA AND BULIMIA NERVOSA. In Developmental-Behavioral Pediatrics (4th ed., pp. 569–581). https://doi.org/https://doi.org/10.1016/B978-1-4160-3370-7.X0001-6

[16] Thomas JG, Bond DS (2014) Review of Innovations in Digital Health Technology to Promote Weight Control. Curr Diab Rep 14(5): 485.

[17] Losing Weight. (2020, August 17). https://www.cdc.gov/healthyweight/losing_weight/index.html.

[18] Byrne, N. M., Sainsbury, A., King, N. A., Hills, A. P., & Wood, R. E. (2017). Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study. International Journal of Obesity, 42(2), 129–138. https://doi.org/10.1038/ijo.2017.206

Just an Exercise Sports Science major sharing as much knowledge as I can!