The human body needs a balanced food supply, enough and not excessive, to grow, to produce energy, to eliminate waste, and to balance and regulate its different metabolisms. Therefore, a diet has to supply the body with appropriate proportions of proteins, lipids, glucides, water, mineral salts, vitamins and cellulose. For example, for a healthy adult, it is estimated that proteins have to supply 10 to 20% of energy, lipids 20 to 25%, and glucides 55 to 70 %.

1°) Energy needs
Individual need of energy is very variable and depends on nutritional habits (as for a weight loss diet). In fact, each individual adapts to what he/she eats and finds a balanced nutrition that might not be suitable to another individual with same weight and lactivities. Therefore and as an example, we estimate that man who weights 65 kg needs 2500 kcal (10500 kJ) per day if he is not active and 4000 kcal ( 16700 kJ) if he is very active.

2°) Protein needs
Proteins essentially play an important role of construction or reconstruction of tissues. Amino acids are basic constituents of proteins: each protein is a particular amino acid chain. Among the twenty amino acids that are supplied by food, eight are essential because our body does not produce them and therefore must be in our food. If one of them is not included in our diet, the whole chain of protein will cease to function.
Animal proteins are of a higher biological quality than vegetable ones. The latter lack one or several essential amino acids. However, proteins derived from animals are associated to bad fat (saturated); that's why it is recommended to consume it with moderation.
Each source of protein has to contribute with half of the total required quantity. A healthy adult needs 1g of proteins per kilogram of weight and per day. The calculation is done on the ideal rather than real weight. Thus, an adult weighing 60 kg needs 60 g of proteins per day, 30g of which must be derived from animals and 30g from vegetables.
1g of proteins supplies 4 cal/17kj.

3°) Carbohydrates needs
The carbohydrates supply covers essentially the needs in dynamic energy ;
It is evaluated that a healthy adult requires up to 5g of carbohydrates (one gram provides 4 kcal) per kilogram and per day. Thus, a 60 kg adult will need 60*5 = 300g of carbohydrates. In nutrition, there are two kinds of carbohydrates:
- ‘rapid' carbohydrates: rapidly and easily digested. These are ‘simple' carbohydrates: lactose (found in milk), fructose (in fruit), sucrose (domestic sugar) .
- ‘complex' carbohydrates: whose digestion is slow and chemical composition is complex. These are cereal, rice, potato and manioc starch.

4°) Lipids needs
Lipids provide the body mainly with its requirements in caloric energy.
1 g of lipids provides 9 cal (or 38 kj).
Lipids are of two kinds that must complete each other in everyday nutrition :
- Animal fat, which is solid in ambient temperature and rich in saturated fat acids and cholesterol;
- Vegetable fat, which is fluid in ambient temperature, rich in unsaturated fat acids and low in cholesterol.
The human body needs around 1g of lipids per kilogram and per day.

5°) Mineral salts and vitamins needs
Except in some particular cases (pregnancy, illness, convalescence, climate changes etc.), a varied and balanced diet largely satisfies the body needs in salts and vitamins.

6°) Waste elimination
Vegetable fibres and water have a cleansing function; because the body does not assimilate them, they constitute the faecal bowl and ensure its progression in the bowels. Thus they actively help avoid constipation.