Whey is best known for its role in building muscle. Proteins are the core of our body: our muscles, hormones, enzymes, antibodies are made of amino acids. These are the constituents of proteins. Proteins are essential to the proper functioning of the human body and their role goes beyond muscle building.
All proteins are made up of 20 amino acids, 8 of which are essential for our body. Our body is not able to manufacture its own amino acids, so we must provide them through our diet. 
And no, protein is not only used when you want to gain weight. It promotes the increase of muscle mass of course, but it also prevents the loss of this mass during a caloric restriction. It also helps reduce the natural loss of muscle and strength, induced by age or inactivity.
 
The choice of the protein to consume will vary according to the objective, the starting morphology of the person and possible food allergies/intolerances.
We will mention here the 4 basic proteins, if you want to know more about all types of proteins, it happens on this article.

Whey concentrate, the base protein 

Inexpensive, it is found very easily in shops. But beware, this does not take away its quality! It has remarkable nutritional qualities and can provide protein quickly assimilated by your muscles after training.
This whey is obtained during the manufacture of cheese: once the water and casein are removed from this product, a whey protein concentrate remains. It is rich in immunoglobulins, peptides, essential fatty acids, branched-chain amino acids, with a high level of leucine, as well as a high amount of glutamic acid, the direct precursor of glutamine. It is presented as a powder which can contain between 30 and 90 % of proteins on dry matter, a dose containing on average 20g of proteins according to the various marks. 
 
How to consume it?
 
Whey concentrate can be consumed at breakfast, as a snack and especially after training to meet your protein needs. It is a protein with a medium-rapid diffusion which has a very interesting assimilation in view of its complete amino acidogram.