There are varied sources of protein such as meat, fish, eggs and milk and they differ greatly in their quality. Higher quality proteins are easier to digest and offer a complete amino acid profile. They have higher biological value. The ability of a protein to adequately satisfy the amount of amino acids required for human growth and repair dictates its biological value.
Foods that contain most all of the essential amino acids are of higher quality. Complete proteins contain all of the essential amino acids. Eggs contain all of the essential amino acids making them a complete and high quality protein.
Protein sources can be categorized broadly into those that are animal based and those that are vegetable based. Animal proteins typically foot the bill of being higher quality, complete proteins. This includes foods such as meat, fish, eggs and cheese. Plant based proteins are of lesser quality as they do not contain all of the essential amino acids and their overall amino acid profile is not sufficient to meet the needs of the body for growth and repair.
However, plant proteins can be combined to create a more complete amino acid profile such as by combining grains (corn, rice etc.) with legumes (kidney beans, split peas, etc.). This is a fairly common practice which results in a perfectly suitable, high quality protein meal.
Some common foods and their protein content:
*Approximate Values; Source Jean Carper’s Total Nutrition Guide