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:
|Essential Amino Acid||mg/g of Protein|
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:
|Essential Amino Acid||Requirement mg/day/62 kg adult||9 large baked potatoes|
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, though gelatin and milk products are exceptions. 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.
- Most unrefined foods contain all the essential amino acids on their own in a sufficient amount to qualify as a "complete protein". Foods that also obtain the highest possible Protein Digestibility Corrected Amino Acid Score (PDCAAS) score of 1.0 are certain dairy products (including whey), egg whites, and soy protein isolate. Other foods, such as amaranth, 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. However, most unrefined plant foods (excepting fruits) provide more than enough of all essential amino acids even after you account for any differences in digestion or protein quality.
- "Protein in diet". Medline Plus Medical Encyclopedia. U.S. National Library of Medicine and National Institute of Health. September 2, 2003. Retrieved 2006-10-28.
- [dead link] http://www.nutritiondata.com/help/analysis-help#protein-quality
- World Health Organization, Protein and Amino Acid Requirements in Human Nutrition http://whqlibdoc.who.int/trs/WHO_TRS_935_eng.pdf, p. 245
- National Nutrient Database for Standard Reference Release 25, Nutrient data for 11357, Potatoes, white, flesh and skin, baked http://ndb.nal.usda.gov/ndb/foods/show/3070?fg=&man=&lfacet=&count=&max=25&qlookup=potatoes&offset=&sort=&format=Full&_action_show=Apply+Changes&Qv=1&Q5733=9&Q5734=1.0&Q5735=1.0
- Interactive DRI for Healthcare Professionals http://fnic.nal.usda.gov/fnic/interactiveDRI/dri_results.php
- 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.
- Woolf, P. J.; Fu, L. L.; Basu, A. (2011). "VProtein: Identifying Optimal Amino Acid Complements from Plant-Based Foods". In Haslam, Niall James. PLoS ONE 6 (4): e18836. doi:10.1371/journal.pone.0018836. PMC 3081312. PMID 21526128.
- McDougall, John (2002). "Plant Foods Have a Complete Amino Acid Composition". CIRCULATION 105.
- Campbell N, Reece J, Mitchell L (1999). Biology. Benjamin Cummings. ISBN 0-8053-6573-7.
- "The majority of plant proteins are incomplete because they lack at least one essential amino acid. As different plant sources are low in specific amino acids, you can combine complementary plant sources to create a nutritionally complete protein. For example, grains supply the essential amino acids missing in legumes, and legumes supply the essential amino acids missing in grains. Eating black beans on a corn tortilla, for instance, supplies your diet with all your essential amino acids." Livestrong.com webpage entitled NUTRITIONAL SOURCES OF ESSENTIAL AMINO ACIDS
- "Tillery points out that a number of popular ethnic foods involve such a combination, so that in a single dish, one might hope to get the ten essential amino acids. Mexican corn and beans, Japanese rice and soybeans, and Cajun red beans and rice are examples of such fortuitous combinations."
- "Quinoa: An emerging "new" crop with potential for CELSS (NASA Technical Paper 3422)" (PDF). NASA. November 2003. Retrieved 2006-10-28.[dead link]
- "Setting the record straight: Vegetables have plenty of protein, and they're complete proteins as well" http://wayback.archive.org/web/20080317001659/http://michaelbluejay.com/veg/protein.html