Basal Metabolism: What It Is, How It Is Measured And Why It Allows Us To Survive
Living beings are not watertight compartments, since we have to obtain energy from the environment to remain over time.
Some taxa obtain energy by converting inorganic matter into organic matter (such as plants and photosynthesis), while all vertebrates obtain this energy through nutrition, whether based on vegetables, meat products and many other sources. organic more.
In addition to needing a minimum amount of energy to not die, we need more or less daily caloric intake based on our work and effort either. It has nothing to do with, for example, the amount of food consumed by a racehorse and a lurking snake in its den. In addition to having different metabolic pathways, the physical work performed by both is not even comparable.
In relation to this whole topic, today we come to bring you a truly interesting term from a biological point of view for researchers, doctors and zoologists alike. Let’s see what he is like basal metabolism: As complex as this concept may sound, we assure you that you will have a detailed idea of it after reading these lines.
General metabolism or metabolic requirements can be defined as the energy demands that an organism requires for the set of biochemical reactions and physicochemical processes that occur in its cells This set of reactions allows living beings to grow, reproduce, keep their physical structures in order and respond to external stimuli, among other things.
Basal metabolism or Basal Metabolic Rate (BMR) refers to the rate of energy expenditure per unit of time that endothermic animals require to remain at rest. In other words, it is the amount of heat (expressed in calories) that is generated in one hour by the subject kept at rest at a temperature of 18 degrees on an empty stomach after 12-14 hours, standardized conditions.
We have just introduced a term that attracts attention and must be explained: endothermy. Let’s lay the groundwork before continuing with more complex terminology.
Endotherms are living beings that use internally generated heat to maintain their body temperature, which tends to remain in a constant range despite environmental inclemencies, unless a pathological condition occurs. This physiological phenomenon is based on a premise: metabolic reactions are not 100% efficient and, therefore, energy “escapes” from the body in the form of heat.
On the other hand, ectotherms are animals that are not capable of generating heat in their metabolic processes, so their only way to thermoregulate is to go to energy sources or move away from them.
It is no coincidence that sunning behaviors are observed above all in reptiles: when a lizard is leaning on a stone “sunbathing,” what it really does is obtain the necessary energy in the form of heat to be able to carry out metabolic processes such as digestion or movement, among other things.
So that, When we talk about basal metabolism (BMR), we are referring only to the heat produced by endotherms which are mammals and birds.
If we wanted to quantify the amount of energy necessary for the survival of a reptile or amphibian, we would use a different term and methodology: the standard metabolic rate (SMR). This follows similar criteria to the basal metabolic rate, but the environmental temperature must be taken into account, since it completely modulates the energy availability of the ectothermic animal.
What other parameters accompany basal metabolism?
This value is very useful, as we will see later, but does not fully explain the individual’s energy demand Before continuing, you should keep the following in mind:
Total energy expenditure (TEG): Basal metabolic rate (BMR) + endogenous thermogenesis (TE) + physical activity (PA)
The World Health Organization (WHO) provides a very good definition of total energy expenditure, in which the BMR plays a very important role: “it is the level of energy necessary to maintain the balance between energy consumption and expenditure. , when the individual has weight, body composition and physical activity compatible with a good state of health.”
As you can imagine, This value fluctuates between individuals Well, you have to pay attention to age, gender, ethnicity, place of origin and many other things.
The basal metabolism represents the minimum cost of the organism so that it can carry out the vital maintenance functions that are not stopped consciously, such as cardiovascular, respiratory, endocrine, central nervous system, renal, hepatic, the immune system and the phenomena of thermogenesis (heat formation).
These “basal” conditions require a specific environment to be quantified: the individual must have slept 10-12 hours, be in a post-absorptive state (not having eaten any food for at least 12 hours) and be under conditions of thermoneutrality and in a state of physical and emotional rest. Of course, you cannot measure a person’s basal metabolic rate if they are on a mountain full of snow fleeing from a bear, since their energy demand is much greater and the situation is beyond normal.
How is basal metabolism measured?
To measure a basal metabolic rate effectively (without using predictive formulas), it is necessary to use direct or indirect calorimetry. In the first case, The amount of heat produced by the organism is measured in airtight chambers with insulating walls Here the stored energy and the energy lost through convection are recorded, after a stabilization period of at least 6 hours.
On the other hand, BMR can also be obtained using indirect calorimetry, a minimally invasive but very effective method. This is based on the uptake of oxygen and release of carbon dioxide: because anabolism requires oxygen and CO2 is released, the amount of heat produced is related to oxygen consumed and CO2 released. Here the respiratory coefficient comes into play, a parameter that we reserve for another opportunity
Basal metabolic rate formulas
If you search online, you will see that there are various calculators that try to estimate your basal metabolic rate without performing any medical tests. Although the indirect calorimetry method is appropriate to obtain a truly reliable value, these programs are based on mathematical formulas that take into account the following factors:
These parameters give us formulas like the following:
If you want to stick with a figure, we can tell you that certain studies have calculated average basal metabolic rates in individuals part of studies that range between 1027 Kilocalories/day and 2499 Kilocalories/day. This is the energy needed to simply exist so, based on exercise and activity, a variable caloric range must be added.
It is striking to know that, approximately, BMR decreases by 1-2% for each decade after 20 years of age, mainly due to the loss of purely fat mass.
Basal metabolic rate and size
It is common (and correct) to think that the net basal metabolic rate will be much higher in an elephant than in a mouse, since their weight moves on different scales and, naturally, a large animal will produce and lose much more heat than a small one. TRUE?
In absolute values this postulation is correct, but things get interesting if the BMR is divided by the mass of the animal. If divided by weight, the metabolic rate of a mouse per gram of tissue is 10 times greater than that of an elephant Although the mechanisms underlying this process are not yet fully understood, it is known that the surface/volume ratio of a small animal is higher, which favors heat loss.
Thus, small endothermic animals tend to have much shorter life cycles, since their cellular metabolism is very fast and tissues and organs fail sooner. If, on the other hand, you see a gecko with the same weight as a mouse, you will discover that it lives up to 7 times longer. Why?: Since the reptile does not generate heat, the energy demand and the work carried out by its body is much lower.
Summary
Fascinating, right? It turns out that, as anecdotal as it may seem, The basal metabolic rate in endotherms determines their life expectancy and vital strategies On a more medical than biological level, in addition, this parameter helps nutritionists and sports professionals know how many calories they should eat per day to maintain, increase or decrease the total mass of a specific organism.
