Food is everything we need to keep us alive: it provides us with energy for the production of heat, work or other forms of energy (through proteins, carbohydrates and lipids), material for the growth and repair of tissues (proteins and minerals), and catalytic material for the functioning of our metabolism (minerals and vitamins).
We nourish ourselves with foods and live on the nutrients they contain — carbohydrates or sugars, proteins and lipids or fats, which provide calories, as well as water, minerals and vitamins, which do not.
One of the most important needs of the body, met by nutrition, is the need for energy: to carry out any kind of work — even simply to stay alive — energy is required.
Through food, the body is able to perform any activity, such as growing, moving and renewing itself. The energy provided by foods is usually calculated using the calorie system: calories indicate the capacity of nutrients to generate energy, which can either be used immediately by the body or set aside as a reserve. Excess energy, for example, can be stored in the form of fats (in adipose tissue) or glycogen (in the muscles and liver), to be drawn upon when needed.
The calorie count, used for example in the well-known points-based diets, indicates only the energy potential of a food, but says nothing about its nutritional value
in terms of vitamins, mineral salts, protein quality, biological functionality and so on; it is therefore not sufficient for assessing the overall nutritional value and effects of foods. In practice, it is wrong to consider a food nutritious simply because it is very high in calories.
The energy provided by foods is calculated using the calorie system. Calories indicate the capacity of nutrients to generate energy, which can either be used immediately by the body or set aside as a reserve. Excess energy, for example, can be stored in the form of fats (in adipose tissue) or glycogen (in the muscles and liver), to be drawn upon when needed.
Technically, one calorie is the amount of heat required to raise the temperature of 1 gram of water from 14.5 to 15.5°C. Nutrients vary in their caloric content: the most caloric are fats, followed by carbohydrates and then proteins.
Carbohydrates are organic compounds derived mostly from plant sources — in the form of sugars, oligosaccharides, starches and fibres — made up of carbon, hydrogen and oxygen, synthesised by plants through photosynthesis. Once in the body, they are converted into carbon dioxide and water, and this process releases the energy we use for vital functions.
Carbohydrates therefore serve to fuel muscular activity and to support the tissues of the heart, liver and nervous system.
The preferred carbohydrates are the complex ones found in bread, pasta and wholegrain cereals, legumes and tubers, which provide slow-release energy. The woody and fibrous parts of all plants, although they do not perform a strictly nutritional function (fibre is indigestible for humans), are also a carbohydrate of great importance to intestinal function, even though they do not serve to deliver energy.
In addition to providing energy, nutrition literally serves to build the body (bones, muscles, tendons) and to renew it — that is, it meets what is known as the plastic requirement. The substances needed for the construction and continual renewal of tissues are numerous: from proteins, of which muscles are composed, to the mineral salts required for bone structure, to water (the human body is made up of approximately 65% water), and so on.
Proteins are the principal organic constituents of cells, the building blocks with which our body constructs and reconstructs itself. They are known as biological effectors: they play a role in the composition of all tissues as well as of blood (haemoglobin), and, in food, are also a source of energy.
And finally, food has a protective function, and with the right approach, a therapeutic one too. Fibres, vitamins, mineral salts and thousands of micronutrients, abundant in healthy foods — we will see which ones, and how to make the most of them — contribute decisively to our vitality, good health, youthfulness and to combating certain diseases.
The calorie count, used for example in the well-known points-based diets, indicates only the energy potential of a food. Proteins in themselves should not be consumed in excess or out of proportion. The percentage of carbohydrates or proteins says nothing about nutritional value in terms of vitamins, mineral salts, protein quality, biological functionality, balance of its components, vitality, taste and pleasure.
For this reason, a correct diet cannot disregard a comprehensive, all-round assessment of each individual's needs.