The term “protein” often conjures up images of a large steak, chicken breast or salmon fillet. But protein, the nutrient, is actually a complex, multifunctional group of molecules called amino acids, which influence everything from coat color to antibody production in the body. In this article we will discuss the role of proteins in the body, the difference between essential and non-essential amino acids, how protein is digested, and how protein quality is defined.
Protein is the main structural component of hair, skin, organs, blood cells and cartilage. It comprises enzymes for metabolism—the hormones that act as the body’s messengers and the antibodies that comprise the immune system. Protein also provides energy, and as mentioned before, amino acids.
What is an amino acid? Amino acids are small molecules made of nitrogen plus other elements organized into units called side chains. The side chains determine the functionality of the amino acid. For example, methionine and cysteine are two amino acids that have sulfur in the side chain and are important for hair coat strength. Dietary amino acids can be divided into two categories: essential amino acids (EAA) and non-essential amino acids (NEAA). EAA must be supplied in the diet because pets cannot synthesize them, whereas NEAA are synthesized by combining parts of EAA with other elements supplied by the body. Conditionally, EAA are not usually required by healthy pets but may be needed during certain metabolic stresses.
How are dietary proteins digested? Dietary proteins are large bulky molecules which require energy and enzyme resources to be broken down into chains of 2 or 3 amino acids that are absorbed from the intestine into the body.
How is protein quality determined? There are two things that determine protein quality: digestibility and EAA content. Protein digestibility is defined as the efficiency of absorption of amino acids from the intestine into the body. Highly digestible proteins provide more readily available amino acids to be used by the body for new protein synthesis. In addition, highly digestible proteins leave fewer undigested amino acids in the large intestine. Undigested amino acids can cause digestive intolerance like flatulence or digestive upset.
There is no single protein source that provides all of the EAA in the correct proportion. So in healthy pets it’s a good idea to use diets with a combination of protein sources in order to balance the contributed amino acids. Protein quality is not determined by ingredients sources but instead by digestibility and EAA content.
Protein, unlike carbohydrates or fats, is not stored in the body. All the proteins in the body have a function and it is critical for overall health that high-quality dietary protein containing EAA are provided daily for normal cell turnover, organ and tissue maintenance, hair coat and skin strength and proper immune system function.