This article will focus on understanding the concept of metabolism and the implications that it can have in supporting the body’s functions and body composition .
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On the other hand, topics of little relevance will not be dealt with, such as, for example, finding out if one’s metabolism is high or low; in fact, it is not possible to discover its size without an accurate instrumental analysis. However, there are techniques for indirect detection of basal expenditure, conceived on large sampling algorithms, and some useful measures to increase energy consumption (which we will see below). Put simply, excluding real pathologies or paraphysiological conditions, the correlation between low and overweight metabolism does not exist; it is rather an alibi.
What’s this
What is metabolism?
By metabolism we mean the set of all the chemical reactions that sustain the life of an organism. The three main functions of metabolism are:
- the conversion of food into energy to support cellular processes
- the conversion of nutrientsand nutritional factors into components necessary for the endogenous synthesis of proteins , lipids, nucleic acids and some carbohydrates
- the elimination of nitrogen waste.
The multitude of reactions that support the three metabolic functions is catalyzed by enzymes that allow organisms to grow and reproduce , maintain the various structures and respond to environmental stimuli.
The word metabolism can also refer to the sum of all the chemical reactions that occur in living organisms, including the digestion and transportation of substances in and between the different cells ; in this case, all the cellular processes are called “intermediate metabolism”.
Types of metabolic reactions
Metabolic reactions can be classified as:
- Catabolic: the breakdown of compounds such as glucosein pyruvate through cellular respiration
- Anabolic: the construction (synthesis) of compounds such as, for example, proteins, carbohydrates, lipids and nucleic acids. Usually, catabolism releases energy and anabolism consumes energy .
The chemical reactions of the metabolism are organized into metabolic pathways , in which a chemical is transformed – through a series of steps – into another compound; each phase is facilitated by a specific enzyme (catalysis).
Importance of enzymes for metabolism
Enzymes (biological catalysts) play a fundamental role on metabolic processes, because they allow to carry out otherwise impossible reactions that require the use of energy, combining them with other spontaneous reactions that instead release energy. The enzymes act as catalysts – they allow a reaction to proceed more quickly – and also allow the regulation of the speed of a metabolic passage, for example in response to changes in the cellular environment or to signals from other cells.
The metabolism determines what is good and what is bad
The metabolic system of a particular organism determines which substances take on the role of nutrients and which of poisonous agent. For example, some prokaryotes (cells other than ours) use hydrogen sulfide as a nutrient, however, this gas proves to be highly poisonous for animals (therefore also for humans).
Metabolic pathways: the same from the bacterium to the elephant
Another striking feature of metabolism is the similarity of the basic metabolic pathways between very different species. For example, the set of carboxylic acids better known as intermediates in the citric acid cycle are present in all known organisms, being in extremely different species such as the single-cell bacterium Escherichia coli and the huge multicellular organisms such as elephants. These similarities in the metabolic pathways are probably due to their early appearance in the evolutionary history and their conservation due to a remarkable efficacy.
What determines the total metabolic consumption?
Total metabolic consumption is determined by:
- Basal metabolism: in turn influenced by age ( growth increases anabolic processes and therefore the energy cost), by the amount of lean and especially muscle mass ( muscles cost much more calories than other tissues), by sex (because correlated the amount of muscle mass ) etc.
- Motor physical activity level
- Digestion and metabolization of nutrients ( diet-induced thermogenesis)
- thermoregulation
- Excess Postexercise Oxygen Consumption(EPOC): it is the calorie consumption induced by the post workout oxygen debt ; the greater and longer the activity has been
- Diseases and pathologies: for example tumors, which significantly increase energy expenditure, or hypothyroidism , which instead decreases it.
Basal metabolism
What is basal metabolic rate?
The basal metabolic rate of an organism is the measure of the amount of energy consumed by all essential chemical reactions. More precisely, by Basal Metabolic Rate (BMR) we mean the rate of energy consumption at rest in the unit of time of endothermic ( warm- blooded ) animals .
What does the basal metabolic rate depend on?
We said, basal metabolic rate is the result of the algebraic sum of energy consumed for essential metabolic processes. On the other hand, each organism has its own basal metabolism, because the physiological properties that characterize it are different.
The higher the number of cells, the higher their activity, the higher the basal cost. The number of cells is attributable to the anthropometric characteristics of the subject and the size of the lean mass (especially muscle). Basal cellular activity, on the other hand, is largely regulated by the action of thyroid hormones ; however, it should be specified that, in a healthy subject, this parameter is not modifiable and works in a more or less identical way for everyone. Not to be overlooked, the anabolic factor of growth; in fact, for development, even at rest, the cells use much more energy than in maintenance conditions.
Various studies show that basal metabolic rate can vary more than decisively among individuals. In particular, work on 150 representative adults of the population in Scotland reported basal metabolic rates from a minimum of 1027 kilocalories per day ( kcal / day) to a maximum of 2499 kcal / day; the average corresponds to 1500 kcal / day. Statistically, the researchers calculated that 62.3% of this variation was attributable to the significant differences in lean body mass . Other factors explaining this variation included: fat mass(6.7%), age (1.7%) and the experimental error, including the difference between the subjects (2%). The rest of the variation (26.7%) was not justified, either by sex or by the size of the tissue of highly organsenergetic as the brain .
Significant differences in basal metabolic rate were also observed when comparing subjects with the same percentage of lean body mass. In another study, by comparing individuals with the same lean body mass, metabolisms 5% higher were 1.28-1.32 times than the lowest 5%. Furthermore, this study reports a case in which two individuals with the same lean mass of 43 kg had BMR of 1075 kcal / day and 1790 kcal / day. This difference of 715 kcal / day is equivalent to covering 10 km of running . However, this study did not take into account the sex, height , fasting status or body fat percentage of the subjects.
Detection of basal metabolic rate
Basal metabolic rate is estimated by measuring energy per unit of time, for example watt (joule / second), ml O2 / min, joule or calories per hour per kg of body mass [j or c (h · kg)]. For practical reasons, in the dietary context, the basal metabolic rate is calculated over 24 hours; in Italy the unit of measurement of kilocalories (kcal) is mainly used.
Correct measurement of basal metabolic rate requires compliance with a strict set of criteria. These include:
- Being in a totally undisturbed physical and mental state
- Stay in a thermally neutral environment
- Maintain a post-absorption state, not post-prandial, but not even in conditions of prolonged fasting.
In bradimetabolic animals, such as fish and reptiles, the equivalent term of standard metabolic rate (SMR) is used. This follows the same criteria as the BMR, but the temperature at which it is measured becomes a very important variable.
Flexibility
What is and what metabolic flexibility entails
Basal metabolic rate is a “flexible” trait, meaning it can be reversibly regulated within individuals. For example, lower outdoor temperatures result in higher basal metabolic rates.
There are two theories that explain how, especially in birds, BMR is regulated in response to temperature:
- Variable maximum model (VMM): according to which the maximum metabolic rate in response to cold (of the summit) would increase during the winter while what can be sustained indefinitely remains a constant fraction of the first
- Variable fraction model (VFM): according to which the vertex metabolism does not change, and the sustained metabolism is a large fraction of the same.
The increase and decrease of the basal metabolic rate is manifested with great relevance especially in certain warm-blooded animals capable of changing their habits according to the seasons (migratory birds, for example). For the human being, it is not exactly the same thing. No great seasonal flexibility is observed and the increase in caloric consumption due to climatic variation is attributable only to the process of thermoregulation.
However, there are other elements that fall within the capacity of human metabolic flexibility, but none of these have innate origins on the species. Habits and lifestyle are heavily affected; for example, the level of motor activity and the way of eating.
Increasing metabolic flexibility increases the ability to adapt to particular conditions such as increasing and reducing calories. This undoubtedly entails a better ability to use the nutrients taken with food without depositing them and a greater potential to oxidize fats in negative calorie balance conditions; ergo, you get less fat, there is the possibility of building more lean mass (obviously in the presence of the right training stimulus) and you lose weight faster.
Metabolism and Body Weight
Influence of metabolism on body weight
We now come to the correlation between metabolism and body weight , or more correctly between the total energy expenditure and the balance between lean and fat mass.
The muscle mass, which is part of the lean mass, is largely responsible for the total calorie expenditure, in movement but also at rest (basal metabolism). Although it is mainly determined by the individual’s predisposition, this can be increased by specific motor exercise. Physical activity then, in addition to directly increasing energy consumption (moving costs calories), also stimulates the metabolism in the immediate post-exercise (EPOC). Training therefore has a threefold effect on the optimization of body composition.
On the other hand, high levels of fat mass negatively affect the balance of the exchange (especially on blood sugar , lipemia and insulinemia ), on the tendency to systemic inflammation , on the appetite- satiety mechanism etc. In short, those who are fat have a greater aptitude for gaining weight and getting sick with metabolic disorders, inflammations, cardio-circulatory pathologies (but not only), joints, etc.
Sport, metabolism and weight loss
On the other hand, many people, while doing sports, do not lose weight. This is mostly due to the intake of excessive calorie levels with the diet; therefore, a hypothetical low cost of basal metabolic rate has nothing to do with it.
Nonetheless, as we said above, there are also very relevant interindividual differences in basal metabolic rate. So, taking for granted the full state of health, to those who unfortunately find themselves with a low basal metabolic rate, all that remains is:
- Calculate the most suitable caloric intaketo be taken with food (refer the topic to more specific articles concerning the low-calorie weight loss diet or the normal- calorie diet )
- Continue to play sports, with the most appropriate strategy for the case
- Attempt to improve your metabolic flexibility.
Which sport to practice?
To promote the right balance between lean and fat mass, it is crucial that sport has the following characteristics:
- Have an adequate load: given by the volume, intensity and density of the stimuli
- Be continuous and systematic, planned and programmed, constantly evaluated and modified
- It is sustainable, pleasant and subjectively appropriate
- Provides a significant aerobicstimulus , which allows you to oxidize reserve fats, but also a short-term anaerobic stimulus focused on strength and hypertrophy, which allows you to build muscle mass.
In this sense, as we have said, physical exercise acts in a multifaceted way on the energy cost and promotes body recomposition .
How to improve your metabolic flexibility?
Simply by changing habits. A lazy and / or inefficient metabolism is the result of a sedentary and monotonous lifestyle .
Those who do not eat all meals should start dividing at least 5-6 per day. Conversely, those who eat too often should try to increase the distance at least between snacks .
If by reducing the number of meals (to a total of 5) you are accused of a great desire to eat, especially carbohydrates, it means that the body is addicted to high availability of glycids in the diet. This is synonymous with poor efficiency in the use of fats. We should therefore roll up our sleeves and force a different distribution of nutrients, limiting carbon hydrates to 45-50% of total calories.
Most people who can’t lose weight have a long series of low-calorie diets behind them . This is wrong, for two reasons. The first is that, if they did not work, these nutritional styles certainly led the subject to insert small incorrect dietary habits (for example, eating a salad for lunch and two pizzasat dinner); this must be corrected. The second concerns the organism’s ability to get used to it. A failed attempt must be followed by a period of maintenance / restoration, because the metabolism (or unconsciously also the mind) tends to evolve saving energy. In this case it would be necessary to re-educate it by “resetting” (cit) these habits. To do this, it is necessary to invest a few months, or rather a year, during which the calories will increase gradually and in small steps. In this case the organism reacts positively: it adapts slowly without significantly accumulating other fat in the fat. At the same time, however, a sort of “habit” of energy surplus occurs. Once this phase is over, you can proceed with the caloric reduction, considerable and above all “healthy”.
It is advisable to distribute fats and carbohydrates correctly. By reducing one or the other macronutrient to the extreme, the metabolism loses the ability to use them correctly. In addition to going to a disadvantage of a possible sporting performance, every single period of “sgarro” would correspond to a poorly efficient and responsible metabolic reaction of the fat deposit .
Last but not least, although scarcely relevant to the topic of the article, we remember that alcohol contributes in an exorbitant way to increase the calorie intake of the diet. Suffice it to say that even in a low-calorie weight loss diet, which roughly reduces 30% of the energy compared to a normal calorie diet (i.e. about -660 kcal in a 2200 kcal), drinking two beers of 660 ml blonde per day compromises the calorie balance at enough to cancel weight loss.