Metabolic energy: what is it and how does it influence health?

Let's see what metabolic energy consists of and how the basal metabolic rate is calculated.

A living being is a complexly organized material whole that exchanges matter and energy with the environment in an orderly fashion. To be considered as such, a living entity must be able to translate the energy consumed from the environment into growth, relationships and reproduction, with the ultimate goal of leaving its genetic imprint on future generations at all costs.

Living beings (in particular humans) are a continuous exchange: we produce heat, consume oxygen, release carbon dioxide and process organic matter at every moment of our lives. Therefore, we have a series of mechanisms that allow us to maintain bodily homeostasis, or in other words, internal equilibrium despite environmental changes. In short: we are alive because we self-regulate beyond the parameters that surround us.

All these concepts can be reduced to their minimum expression, which is a cell dividing by mitosis and giving rise to a new lineage or, failing that, replacing a tissue that has been damaged. To understand all these basal mechanisms, it is necessary to be clear about a series of concepts, the most important of which are those related to the definition and functionality of metabolic energy.. Stay with us, because we will tell you all about it in the following lines.

What is metabolic energy?

Metabolism is defined as the quality that living beings have of being able to change the chemical nature of certain substances.. On a practical level, this set of processes is essential for cells to grow, divide, maintain their structures over time and respond to stimuli, among other things.

The "problem" is that, for the production of movement or the synthesis of macromolecules, cell bodies require energy. Thus, the behavior of living things the behavior of living beings is encoded (to a large extent) on the basis of obtaining energy from the environmentThe cells of living organisms are then able to use this energy to carry out the relevant biochemical reactions and physicochemical processes.

On the basis of all these processes, a number of immovable generalities can be established. Among them, we find the following:

• Cells associate reactions: processes that release energy (exergonic) allow energy-requiring reactions (endergonic) to occur.
• Cells synthesize carrier molecules that capture energy from exergonic reactions and carry it to endergonic reactions. ATP is a clear example of this.
• Cells regulate the rate of chemical reactions through enzymatic activity.

The ATP molecule (adenosine triphosphate) is of particular interest to us. (adenosine triphosphate), because cells use it to capture, transfer and store the free energy needed to perform chemical work. Understanding metabolic energy without ATP is an impossibility, as this molecule functions as a clear currency of exchange at the energy level.

What does metabolic energy translate into?

Metabolic energy can be understood as energy that is generated by living organisms thanks to ATP. is generated by living organisms through chemical oxidation processes (at the cellular level), a product of the food they ingest.. This parameter can be understood in different ways, but we find it most useful to apply it to the daily reality of the human being. Let's get down to it.

Basal Metabolic Rate (BMR)

The basal metabolic rate (BMR) is the minimum amount of metabolic energy required by the organism to stay alive. In a resting state, although it may not look like it, your body is consuming 60 to 75% of the calories ingested, as it requires that energy to keep the body alive.It requires that energy to keep the heart pumping, to keep you breathing, and even to keep the mind functioning properly.

At basal state, the human brain can consume about 350 calories a day, that is, 20% of the BMR. It is not surprising that we feel tired after a long day of study, because this organ is literally a real focus of burning fat and other energy resources. In addition to thinking, breathing and Blood pumping, metabolic energy is also used in cell growth, body temperature control, nerve function and muscle contraction (both voluntary and involuntary). (both voluntary and involuntary).

This value can only be reliably calculated by a nutritionist, as it depends on factors intrinsic to the individual and certain environmental parameters. In any case, a rudimentary estimate can be obtained using the following equations:

• BMR in men = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5
• BMR in women = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161

Total energy expenditure (TEE)

Total energy expenditure is similar to the basal metabolic rate, but in this case the physical activity performed by the individual is taken into account.. We do not necessarily understand "physical activity" as running in a marathon, because standing at a bar, working as a waiter or simply walking to a specific place is an additional effort beyond the maintenance of vital functions.

In addition to physical activity, total energy expenditure also takes into account endogenous thermogenesis (TE), which in turn encompasses the thermic effect of food (ETA).. The latter parameter reflects the energy required to digest, absorb and metabolize nutrients. In this case, the metabolic energy directed to the process and obtained as a result of it depend on the nature of the food and its mixtures in the diet, but it accounts for approximately 10% of the total energy consumed.

Thus, we can gather all the terms included so far in a simple equation, which reflects where the metabolic energy obtained after the ingestion of organic matter from the environment goes:

Total energy expenditure (100%): Basal metabolic rate (70%) + physical activity (20%) + endogenous thermogenesis (10%).

Again, it is necessary to emphasize that these values vary widely between individuals. For example, a very sedentary person will spend 10% of energy on non-voluntary physical activity (getting up, going shopping or walking to work), whereas an athlete will use 50% of the calories consumed to exercise his muscles and body.

In addition to this, it is worth noting that the basal metabolic rate decreases by 1-2% for every decade after the age of 20. Thus, statistically, an 80-year-old resting person will burn fewer calories than a 20-year-old, simply because of his or her physiology and slowed metabolism.

Metabolic energy in other animals

We humans tend to focus on our own species, but we must not forget that what has been described so far is applicable to all homeothermic living beings, i.e. those that can maintain their metabolic energy in other animals.that is, those that can maintain a body temperature in spite of environmental changes (mammals and birds).

Beyond numbers and percentages, it is really interesting to know that animals make a clear exchange when it comes to obtaining metabolic energy. For example, when a cheetah hunts a herbivorous mammal, it is expending an astronomical amount of energy during the chase race in order to find prey. Is it worth it?

The theory of optimal foraging (TFO) is a predictive model of behavior that attempts to explain the behaviors of living organisms based on this premise.. This postulation announces the following: to maximize fitness, an animal adopts a foraging strategy that provides the greatest benefit (energy) at the lowest cost, maximizing the net energy obtained.

Thus, an animal will not eat anything that causes it to expend more energy in foraging than it obtains in consumption. Perhaps now you understand why, for example, some huge predators (such as bears) completely ignore small flying birds and other vertebrates belonging to the microfauna: it is simply not worthwhile for them to try to hunt them energetically.

Summary

As you have seen, the subject of metabolic energy ranges from ATP and the cell to the behavior of living organisms.. Organisms are open systems and, as such, we continuously exchange matter and energy with the environment. As such, we adapt in order to maximize the efficiency of our habits in order to stay longer and increase our chances of survival.

In the end, it all comes down to a balance: if what is gained outweighs what is spent, it is usually evolutionarily viable. If something brings more benefit than harm, it usually helps animals to survive one more day in order to reproduce.

Bibliographical references:

• Bonfanti, N., Fernández, J. M., Gomez-Delgado, F., & Pérez-Jiménez, F. (2014). Effect of two hypocaloric diets and their combination with physical exercise on basal metabolic rate and body composition. Nutrición Hospitalaria, 29(3), 635-643.
• Gutierrez, G. (1998). Foraging strategies. Handbook of experimental behavioral analysis, 359-381.
• Redondo, R. B. (2015). Resting energy expenditure. Assessment methods and applications. Rev Esp Nutr Comunitaria, 21(Suppl 1), 243-251.
• Vázquez Cisneros, L. C., López-Espinoza, A., Martínez Moreno, A. G., Navarro Meza, M., Espinoza-Gallardo, A. C., & Zepeda Salvador, A. P. (2018). Effect of feeding frequency and timing on diet-induced thermogenesis in humans, a systematic review. Hospital Nutrition, 35(4), 962-970.