Every food is made up of several nutrients. It is the quantity and quality of nutrients that provide nutritional value. The ability of the human body to digest and absorb nutrients from food given also determines its nutritional value.

There are six major classes of nutrients:

These categories can be classified as either :

Macronutrients (needed in relatively large amounts). These are :
  • lcarbohydrates (which also includes fiber),
  • lipids (fats),
  • lproteins,
  • water

The role of macronutrients (excluding fiber and water) provide energy and structural materials. These are amino acids, which are the basic elements for the construction of proteins, lipids which are constructed from cell membranes and some signaling molecules.

Some of the structural material can be used to generate energy internally, and in this case it is measured in kilocalories.

Carbohydrates and proteins provide about 4 kcal of energy per gram, while fats provide 9 kcal per gram.

However, the net energy absorbed depends on the efforts of digestion and absorption required for assimilation, which vary considerably from one nutrient to another.

Micronutrients (needed in smaller quantities). These are :
  • minerals
  • vitamins.

Vitamins, minerals, and water do not provide energy, but are required for other reasons. A third class of food materials, the fibers (that is to say digestible material such as cellulose), is also necessary, for reasons both mechanical and biochemical.

Other micronutrients, antioxidants and photochemical compounds have an effect on the functioning of body systems. Their necessity is not as vital as in the case of, for example, vitamins. But there is evidence that they play a major role in health

Most foods contain a mixture of some or all of the categories of nutrients, together with other substances, such as various toxins. Some nutrients can be stored internally (eg, the fat soluble vitamins), while others are expected to be consumed more or less continuously.

Needs a nutrient or energy, defined by scientists CNERNA-CNRS, are defined as the quantity of the nutrient or energy required for maintenance (or maintenance), metabolic and physiological functioning of healthy individual (homeostasis) including needs related to physical activity and thermoregulation, and the requirements for certain periods of life such as growth, pregnancy and lactationn.

The recommended dietary intake (RDI) are equal to the measured average nutritional needs of a group of individuals, which are added 2 standard deviations représentatntb most often 15% of the average statistical margin of safety to account for interindividual variability and allow cover the needs of the majority of the French population, 97.5% of individuals.

lNational Health and Nutrition Program (PNNS), which aims to improve the general health of the entire French population by acting on one of its major determinants: Nutrition, finds that :

  • The role of nutrition as a protective factor or a risk of the most common diseases in France is becoming better understood, whether it is cancer, cardiovascular disease, obesity, osteoporosis, or the Type 2 diabetes
  • Adequate nutrition is a factor in health protection
  • Advances in research have clarified the role of inadequate dietary intake and lack of physical activity in the determination of many cancers and cardiovascular diseases, which account for over 55% of the 550,000 annual deaths in France