A complete protein (or whole protein) is a source of protein that contains an adequate proportion of all nine of the essential amino acids necessary for the dietary needs of humans or other animals. Some incomplete protein sources may contain all essential amino acids, but a complete protein contains them in correct proportions for supporting biological functions in the human body.
The following table lists the optimal profile of the essential amino acids, which comprises a complete protein, as recommended by the Institute of Medicine's Food and Nutrition Board:
The following table shows the amino acid requirements of adults as recommended by the World Health Organization calculated for a 62-kilogram adult, and the amino acid profile of 2530 kilocalories of baked potatoes (9 large baked potatoes), which comprise a day's worth of calories for a 62-kilogram (136 lb.) adult:
Nearly all foods contain all twenty amino acids in some quantity, and nearly all of them contain the essential amino acids in sufficient quantity. Proportions vary, however, and some foods are deficient in one or more of the essential amino acids. Though some vegetable sources of protein contain sufficient values of all essential amino acids, many are lower in one or more essential amino acids than animal sources, especially lysine, and to a lesser extent methionine and threonine. However, as shown in the example of potatoes, above, nearly all foods provide sufficient amino acids to satisfy human requirements.
Consuming a mixture of plant-based protein sources can increase the biological value of food. For example, to obtain 25 grams of complete protein from canned pinto beans requires consuming 492 grams (423 kcal); however, only 364 g of pinto beans (391 kcal) are required if they are combined with 12 grams of Brazil nuts. Complementary proteins need not be eaten at the same meal for your body to use them together. Studies now show that your body can combine complementary proteins that are eaten within 24 hours.
According to Dr. John A. McDougall, "any single one or combination of these plant foods provides amino acid intakes in excess of the recommended requirements...it is impossible to design an amino acid–deficient diet based on the amounts of unprocessed starches and vegetables sufficient to meet the calorie needs of humans. Furthermore, mixing foods to make a complementary amino acid composition is unnecessary."
Sources of complete protein
Generally, proteins derived from animal foods (meats, fish, poultry, eggs) are complete. Proteins derived from plant foods (legumes, grains, and vegetables) tend to have less of one or more essential amino acid. Some are notably low, such as corn protein, which is low in lysine and isoleucine.
Certain traditional dishes, such as Mexican corn and beans, Japanese soybeans and rice, and Cajun red beans and rice, combine grains with legumes to provide a meal that is high in all essential amino acids.