Basal metabolism
Definition
Basal metabolic rate corresponds to the maintenance of homeostasis (internal stability of the organism) in an awake or resting subject. In other words, it's the transformation of nutrients into energy to ensure our body's vital functions (the heart, liver, brain and kidneys account for almost half of basic metabolism).
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60% of energy is expended by basic metabolism, 10% by diet-induced thermogenesis (the process by which the body produces heat) and 30% by physical activity (sport and movement combined).
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2 phases
Basic metabolism can be broken down into two phases:
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Catabolism: this is the process of breaking down macro-nutrients into small, unitary molecules. When degradation is complete, energy is produced. For example, when we eat bread, the carbohydrates it contains are broken down into glucose, which, once fully degraded, will be used as a source of energy for our cells.
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Anabolism: this is the process of synthesis (manufacture) from energy reserve molecules and intermediate molecules. For example, after the breakdown of carbohydrates into glucose, one part is used as energy and another part is stored as glycogen in our liver.
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Metabolism and weight
Many believe that a person's morphology is linked to their metabolism. So, if a person's metabolism is slow, they'll be thought to store weight more easily, which encourages weight gain. In reality, the opposite is true. Basal metabolic rate depends on body mass. In other words, a person with a heavier build will need more energy to maintain this greater mass, so metabolism will naturally be faster.
Metabolism and sport
Sport does indeed boost metabolism, but not just any sport! As explained above, it's body mass that counts. If you practice a resistance sport (crossfit, bodybuilding, pole dancing, etc.), you'll build up your muscle mass, which means your basic metabolism will adapt by burning more energy to maintain this extra mass.
Sport also tends to reduce the production of ghrelin, the appetite hormone. In concrete terms, not only do you increase your energy expenditure, but you also reduce your intake (appetite reduction). This is what leads to weight loss. However, it's important to find the right balance: if you reduce your appetite too much, you also run the risk of reducing your energy resources, which can lead to a slower metabolism.
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Metabolism and weight loss
The rule is simple: if you want to lose weight, you need to reduce your intake and increase your energy expenditure. However, if you cut your intake too much and don't eat enough, your body will go into a state of starvation, slowing down your metabolism and leading to slower weight loss. Moderate, gradual weight loss won't affect your metabolic rate, which is why it's so important to keep a close eye on your progress.
Metabolism is rarely the sole cause of weight gain, except in specific cases such as hypothyroidism.
Metabolism and intestinal microbiota
The intestinal microbiota is made up of billions of bacteria, representing around 2 kg. It is sometimes referred to as the “second brain” because of its crucial role in many processes, including carbohydrate metabolism, the synthesis of hormones such as serotonin, ghrelin, leptin and adrenalin, and the optimal absorption of vitamins and minerals.
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An unbalanced microbiota, or dysbiosis, can lead to weight gain for a number of reasons, such as :
Chronic low-grade inflammation caused by increased intestinal permeability,
Reduced production of the satiety hormone leptin,
increased fatty acid storage.​
To maintain a healthy intestinal microbiota, it's essential to eat a varied diet based on unprocessed foods, and rich in plant foods (particularly vegetables and legumes), as fiber nourishes the gut's good bacteria.
Studies have shown a correlation between a microbiota low in diversity and fiber, and weight gain. In one experiment, researchers transplanted the microbiota of an obese person into a group of mice, and that of a healthy person into another group. Although both groups were placed in an identical environment, the mice receiving the obese microbiota gained significantly more weight.
Conclusion
The rate of our basic metabolism is determined by our genes and our body mass. However, it is possible to increase it through physical activities such as weight training, crossfit or pole dancing. What's more, studies have shown that a healthy, diverse intestinal microbiota helps maintain a stable weight, while an impoverished, unbalanced microbiota can promote weight gain over the long term.
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