While the need for macronutrients is measured in grams, that for micronutrients is expressed in milligrams and in some cases in micrograms.
Nutrients provide us with:
- chemical energy (carbohydrates and lipids provide the body with the energy necessary to support the various bodily functions);
- plastic substrates (proteins are a class of molecules fundamental for the synthesis of new tissues or for the repair of existing ones);
- regulatory molecules (vitamins, proteins and various minerals intervene at various levels, regulating the development of innumerable metabolic reactions);
- hydration (water).
The energy contained in the macronutrients is not released all at once, but rather gradually, as the various metabolic reactions follow one another. In any case, this energy cannot be used directly by the cells but must be addressed in advance. to the synthesis of ATP. This molecule possesses a high energetic charge, as it is chemically unstable, therefore capable of transforming itself with extreme ease into a more stable by-product, releasing energy.
The conversion of one mole of ATP into ADP releases 7.3 Kcal of readily usable energy.
Since the energy provided by ATP supports all forms of biological work, it is the energy currency of our cells. Despite the importance of this molecule, the organism does not have large stocks of ATP. In fact, about 80-100 grams of ATP are crammed into the human body, capable of satisfying energy demands for only a few seconds.
For this reason, in order to keep energy levels constant, "ATP" must be continuously produced through the oxidative catabolism of nutrients.
is the amount of heat required to raise the temperature of 1 g of water by 1 ° C, bringing it from 14.5 to 15.5 ° C
In reality, it is too small a parameter to express the energetic movements of the organism. For this reason a thousand times larger size is used, called kilocalorie (Kcal)
The Kcal does not refer to the food source. For example, a bar of chocolate provides more or less the same calories as a dish of seasoned pasta. Although the amount of energy is the same, several factors change, including the weight of the food (lower for chocolate) and the fate of the individual nutrients.
The organism, in fact, uses nutrients in a different way, directing them towards different metabolic pathways depending on whether they are carbohydrates, proteins or lipids.
The energy supplied by food can also be expressed in Kilojoules:
- The kilojoule (KJ), used in Anglo-Saxon countries, corresponds to the energy needed to move the mass of 1 kg by 1 m in 1 sec.
- One kilocalorie equals 4.186 kilojoules (1 Kcal = 4.186 KJ)
To calculate the energy balance of an organism it is necessary to evaluate the energy taken with food (energy inputs) and the energy expenditure in the form of biological work and heat transferred to the environment (energy outputs).
For further information: Energy requirement and basal metabolism
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