Nutrients and their functions
Each food consists of a mixture of substances called NUTRIENTS, classifiable as:
- macronutrients (carbohydrates, lipids and proteins);
- micronutrients (vitamins and minerals);
- water.
While the need for macronutrients is measured in grams, that of 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).
Energy from Food
Our body has a continuous need for chemical energy, which it obtains through the catabolism of the various macronutrients (glucides, lipids and proteins).
The energy contained in the macronutrients is not released all at once, but with a certain gradualness, as the various metabolic reactions follow one another. In any case, this energy cannot be used directly by the cells but must be previously addressed to the synthesis of ATP. This molecule has a high energy charge, because it is chemically unstable, so it can easily transform into a more stable by-product, releasing energy.
The conversion of a mole of ATP into ADP liberates 7.3 Kcal of readily usable energy
Since the energy provided by the ATP supports all forms of biological work, it is the energy currency of our cells. Despite the importance of this molecule, the body does not have large stocks of ATP. In the human body, in fact, about 80-100 grams of ATP are crammed, able to satisfy energy requests only for a few seconds.
For this reason, in order to maintain constant energy levels, ATP must be continuously produced through the oxidative catabolism of nutrients.
Energy measurement unit
Calorie is the unit of measurement used to express both the chemical energy content of food and the body's energy expenditure in various functional processes.
The calorie 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 body's energy movements. For this reason we use a size that is a thousand times larger, called kilocaloria (Kcal)
Kcal do not refer to the food source. For example, a chocolate bar provides more or less the same calories as a seasoned pasta dish. Despite the amount of energy is the same, various factors change, including the weight of the food (lower for chocolate) and the fate of individual nutrients.
In fact, the body uses nutrients differently, orienting 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 in 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 assumed with food (energy inputs) and energy expenditure in the form of biological labor and heat transferred to the environment (energy outputs).
CONTINUE: Energy needs and basal metabolism »
