Every living being is made up of billions of cells . Health is maintained thanks to food, which provides our body with all the food principles necessary to:

• have the energy to preserve its vital functions and activities

• build and renew all its cells and tissues

• adjust and maintain its reactions, its metabolism

  Through metabolism the body derives from food the energy necessary to perform all vital functions (breathing, moving, making the heart beat ...). The unit of measurement of energy is the kilocalories (or a thousand calories, with the symbol Kcal). A calorie is the amount of heat needed to pass 1 liter of water from 19 to 20 degrees.

All food principles supplied by food can be divided into large categories : macro and micro-nutrients.

Macronutrient dietary principles: sugars or carbohydrates (carbohydrates, glucides, saccharides)

They are simple (present in common sugar, milk, honey) and complex (found in bread, pasta, rice, potatoes, corn). They are the fuel for our muscles, they are readily available and provide about 4 kcal per gram. They possess numerous essential biological functions.

The main carbohydrate deposits in our body are in the liver in the muscles. The reserve of carbohydrates in our body is limited to around 2000 Kca l. When these reserves are exhausted - after 24 hours of fasting or intense activity - the glucose needed to live is synthesized starting from the muscle proteins.

About 55-60% of daily calories should come from complex carbohydrates.

Macronutrient dietary principles : fats (lipids)

It's a vast family of substances. Based on the chemical bonds within them, they are divided into saturated fats (solids at room temperature, such as butter) and unsaturated fats (liquids at room temperature, such as oil). They are an important energy reserve : each gram of fat supplies 9 kcalories. They are used in the formation of the membranes that surround the cells, they are precursors of many hormones and of provitamin D. The adipose tissue represents the main energy source of reserve for our body and forms an insulating layer and mechanical protection of internal organs.

In the daily diet, fats should not exceed 20-30% of the total intake and it is preferable to consume polyunsaturated vegetable oils, which provide "good" vitamins and fats.

There is a group of essential unsaturated fatty acids, which the body does not know how to produce by itself and must be taken with the diet: linoleic acid (omega 6), linolenic acid (omega 3) and arachidonic acid (omega 6), are also they are constituents of cell membranes; regulate the maintenance of blood vessels and the efficiency of the nervous system. They are called "Vitamin F" and are found in various vegetable oils, fish fat, oil seeds, dried fruit.

Macronutrient dietary principles : proteins (protides)

They are the food principles found in foods of animal origin (meat, milk, eggs, fish) and vegetables (soy, wheat gluten, legumes). They form muscles, hormones and the immune system, they are receptors on cell membranes. They are formed by chains composed of 20 different units called amino acids, of which nine are essential because the body does not produce them and must be taken with the diet. An excessively high protein diet is dangerous to health. In fact, the waste products of protein metabolism are toxic to the body. One gram of protein provides 4 Kcalories. About 15-20% of daily calories should be of protein origin, about one gram for every pound of body weight.

Micronutrient dietary principles: vitamins, mineral salts and water

It does not have calories and only small quantities are needed, but they are very important regulators of vital functions. With the exception of only vitamin D (which can be produced by the body through exposure to the sun), all non-caloric dietary principles are essential, ie they must be introduced with food because the body is not able to produce them.

Vitamins : they intervene in the mechanisms of growth, blood coagulation, vision, iron absorption, prevention of aging processes and some diseases. They are divided into two groups: - water - soluble (soluble in water), easily absorbed by the intestine and eliminated, if in excess, through urine. They are the Vitamins C, B1, B2, B6, B12, PP, H, F, pantothenic acid, folic acid. - liposoluble (soluble in fats), absorbed in the intestine together with fats and then accumulated in the liver and adipose tissue in considerable quantities (with the risk of overdosing). They are little alterable to temperature variations but sensitive to oxygen. They are the Vitamins A, D, E, K.

Minerals : trace elements, contribute to the formation of bones and teeth, are activators of metabolic reactions and keep the internal and external environment constant to the cells. In humans they represent about 6% of body weight. Many mineral salts are related to each other: the excess of one limits the absorption of the other or carries out opposite actions. Even if present in small quantities, they are indispensable for health. Examples of mineral salts: sodium (Na), chlorine (Cl), potassium (K), calcium (Ca), phosphorus (P), magnesium (Mg), iron (Fe), zinc (Zn), iodine (I).

Water (H2O) : represents about 60% of body weight in adults and performs various functions in the balance of the body, in metabolism, in circulation. The quantity of water produced with the metabolism is not sufficient to cover the daily requirement. Under normal conditions, the daily water change corresponds to 15% of the body weight in the first months of life and about 10% in the adult.

To distinguish the different dietary principles present in foods, attention must be paid to the labels.