Complete protein

Main article: Protein (nutrient)

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.^[1] 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:^[2]

Essential Amino Acid	mg/g of Protein
Tryptophan	7
Threonine	27
Isoleucine	25
Leucine	55
Lysine	51
Methionine+Cystine	25
Phenylalanine+Tyrosine	47
Valine	32
Histidine	18

Nearly all whole foods contain protein, and nearly all forms of protein contain all twenty protein-forming amino acids in some quantity. However, proportions vary, and some forms of protein are partly lacking in one or more of the essential amino acids. Meals prepared with a mix of protein foods can provide a better balance of the essential amino acids and therefore a more complete protein source. Apart from some exceptions such as quinoa or soybeans, vegetable sources of protein are more often lower in one or more essential amino acids than animal sources, especially lysine, and to a lesser extent methionine and threonine.^[3] Nonetheless, although cereal protein is particularly low in lysine compared to animal protein, even the lysine in cereals is adequate for adult needs.^[3] Because of growth, children and infants have a greater requirement for complete protein than adults.^[3]

A variety of proteins in the diet is one way of assuring that the body's amino acid needs are met. All the essential amino acids can be obtained on their own from various everyday plant sources, which, contrary to popular belief, do not need to be combined in the same meal (see Protein combining).^[4]

Sources of complete protein

• Generally, proteins derived from animal foods (meats, fish, poultry, cheese, eggs, yogurt, and milk) are complete, though gelatin is an exception.^[1] Proteins derived from plant foods (legumes, grains, and vegetables) tend to be limited in essential amino acids. Some are notably low, such as corn protein, which is low in lysine and tryptophan.^[5]
• Some foods contain all the essential amino acids on their own in a sufficient amount to qualify as a "complete protein". Complete protein foods that also obtain the highest possible PDCAAS score of 1.0 are certain dairy products (including whey), egg whites, and soy protein isolate. Other foods, such as amaranth, Aphanizomenon flos-aquae^{[citation needed]}, buckwheat, hempseed, meat, poultry, Salvia hispanica, soybeans, quinoa, seafood, and spirulina also are complete protein foods, but may not obtain a PDCAAS score of 1.0.^[1][6]

Notes

1. ^ ^{a b c} "Protein in diet". Medline Plus Medical Encyclopedia. U.S. National Library of Medicine and National Institute of Health. September 2, 2003. http://www.nlm.nih.gov/medlineplus/ency/article/002467.htm. Retrieved 2006-10-28. 
2. ^ Recommended by the Institute of Medicine's Food and Nutrition Board http://www.iom.edu/CMS/3788/4576/4340.aspx http://www.nutritiondata.com/help/analysis-help#protein-quality
3. ^ ^{a b c} Young VR, Pellett PL (1994). "Plant proteins in relation to human protein and amino acid nutrition" (PDF). AMERICAN JOURNAL OF CLINICAL NUTRITION 59 (5 Suppl): 1203S-1212S. PMID 8172124. http://www.ajcn.org/content/59/5/1203S.long. 
4. ^ "Vegetarian Diets". United States Department of Agriculture. http://www.mypyramid.gov/tips_resources/vegetarian_diets.html. Retrieved 2008-05-12. 
5. ^ http://www.faqs.org/nutrition/Ca-De/Corn-or-Maize-Based-Diets.html Retrieved 23 June 2010
6. ^ "Quinoa: An emerging "new" crop with potential for CELSS (NASA Technical Paper 3422)" (PDF document). NASA. November 2003. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19940015664_1994015664.pdf. Retrieved 2006-10-28.