What are Proteins?

Proteins are versatile macromolecules present in all living systems and serve vital functions in practically all biological processes: they contribute to the growth and maintenance of muscle mass, aid in the maintenance of normal bones, function as catalysts, play a role in the transport and storage of other molecules such as oxygen, provide mechanical support as a constituent of some structures of the human body, are the major component of the chemical structure of antibodies, which causes them to intervene directly in the functioning of the immune system, are essential in muscular contraction, transmit nerve impulses, and play a role in DNA synthesis and cell division.

Proteins consist of hundreds or even thousands of smaller units we call amino acids, which are connected by peptide bonds and form long chains. There are essential, semi-essential and non-essential amino acids. Essential amino acids are those that cannot be synthesised by the body itself and therefore must be acquired by food intake. Semi-essential amino acids are created inside the body from essential amino acids, and non-essential amino acids can be obtained from certain food but can also be produced by the body.

Some protein sources, such as milk and eggs, have high biological value proteins that provide the 9 essential amino acids (leucine, isoleucine, valine, lysine, methionine, phenylalanine, threonine,tryptophan, and histidine), among others. In a vegetarian diet, it is necessary to combine different foods to obtain all essential amino acids and meet daily protein intake requirements.

Major dietary sources of protein include red meat, chicken and eggs, fish, milk and dairy products, soy and legumes (i.e. beans, chickpeas, and lentils).

Positive actions of Proteins:

  • Contribute to muscle mass growth
  • Plays a role in the maintenance of muscle mass
  • Plays a role in the maintenance of normal bones


Berg J.M., Tymoczko J.L, Stryer L. Biochemistry. 5th edition. New York: W. H. Freeman; 2002.

EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA); Scientific Opinion on the substantiation of health claims related to protein and increase in satiety leading to a reduction in energy intake (ID 414, 616, 730), contribution to the maintenance or achievement of a normal body weight (ID 414, 616, 730), maintenance of normal bone (ID 416) and growth or maintenance of muscle mass (ID 415, 417, 593, 594, 595, 715) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal 2010;8(10):1811. [ 24 pp.]. doi:10.2903/j.efsa.2010.1811.

Pasiakos, S. M. et al. The Effects of Protein Supplements on Muscle Mass, Strength, and Aerobic and Anaerobic Power in Healthy Adults: A Systematic Review. Sports Medicine. 2014;45(1):111-131. doi:10.1007/s40279-014-0242-2

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