The body daily rebuilds tissue as part of normal regeneration. For example, skeletal muscle tissue is renewed quite fast: it takes 1.5 to 3 months to completely renew the muscles in arms and legs! We need not just any protein. Apart from the amount of protein, quality is important as well. Dairy protein is considered to be of high quality.

 Protein quality is defined by the amount of so-called essential amino acids. Proteins are built from long chains of various amino acids. During digestion in the intestines, proteins are broken down into amino acids. The body uses amino acids to make new proteins for muscles and bones.

Some of these amino acids can be made by the body, but others (the essential amino acids) have to be taken from food. Proteins with higher amounts of these essential amino acids, like dairy proteins, are regarded as being of a higher quality for the body.

Protein quality also refers to digestibility: how efficiently can the body use proteins from food. Processing such as heating influences the digestibility of the proteins.

Plant-based proteins need more processing to be edible. On top of that they contain less essential amino acids, both leading to a lower quality.