The word protein comes from a Greek word mean "that holds the first place." They consist of chains of amino acids of lengths, shapes, compositions and different functions and distinct. Proteins are the main structural components and functional cells of the body: enzymes, transport molecules for blood and cell membranes, hair, nails, etc.. It is therefore mandatory to consume more than enough to maintain good health.

There are 22 amino acids 9 are therefore recognized as being essential: Valine, Leucine, Isoleucine, Threonine, Methionine, Phenylalanine, Tryptophan, Histidine, Lysine, which all come from animal protein.

The other amino acids (that our bodies can synthesize) conditionally indispensable, cystine, cysteine, tyrosine, taurine, glycine, arginine, glutamine, proline, alanine, serine, asparagine, aspartic acid and glutamic acid that `there are more special in nature and in plants.

It is mainly in the liver that amino acids not used are transformed into urea, ammonia and uric acid. Urea is a neutral molecule and is easily excreted in urine. In consequence, ammonia and uric acid, when produced in excess, can have adverse health effects: toxicity, acidity, excretion of other alkaline minerals.

There are a number of factors that determine whether the amino acids are used in the synthesis of new proteins or are to be burned to provide energy

1. The law of all or nothing All the amino acids necessary for the elaboration of `given protein must be present at the same time and in sufficient quantity in the same cell. As the essential amino acids can not be stored,those who are not used immediately in the synthesis are either oxydised to produce energy or converted into carbohydrates or fat.

2. A sufficient energy intake: For the synthesis of proteins to take place under optimum conditions, carbohydrates or lipids present in the diet should provide enough energy for the production of ATP

3. Nitrogen balance: There is talk of positive nitrogen balance when the rate of protein synthesis is higher than the rate of degradation and destruction (which is normal in growing children and pregnant women). It is also positive when the tissue grow back or to heal, a result of an illness or injury. A positive nitrogen balance still indicates that the amount of protein entering the tissue is higher than the amount that is degraded or used to produce energy savings.

4. Hormonal regulation: Certain hormones called anabolic hormone accelerates protein synthesis and growth. The effects of these hormones vary continuously throughout life.

Note: The proteins are abundant in the plant world. A balanced vegan diet therefore provides ample protein to meet our needs, while a diet of meat (animal source), contains too much: