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Protein combining or protein complementing is a dietary theory for
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
nutrition that purports to optimize the biological value of protein intake. According to the theory,
vegetarian Vegetarianism is the practice of abstaining from the consumption of meat (red meat, poultry, seafood, insects, and the flesh of any other animal). It may also include abstaining from eating all by-products of animal slaughter. Vegetariani ...
and
vegan Veganism is the practice of abstaining from the use of animal product—particularly in diet—and an associated philosophy that rejects the commodity status of animals. An individual who follows the diet or philosophy is known as a vegan. ...
diets may provide an insufficient amount of some
essential amino acids An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life form ...
, making protein combining with multiple foods necessary to obtain a complete protein food. The terms ''complete'' and ''incomplete'' are outdated in relation to plant protein. The position of the
Academy of Nutrition and Dietetics The Academy of Nutrition and Dietetics is a 501(c)(6) trade association in the United States. With over 112,000 members, the association claims to be the largest organization of food and nutrition professionals. It has registered dietitian n ...
is that protein from a variety of plant foods eaten during the course of a day supplies enough of all essential amino acids when caloric requirements are met. Though it is undisputed that diverse foods can be combined to make up for their respective limiting amino acids, a general consensus has emerged among nutrition scientists and writers contrary to the original vegetarian nutrition dogmas of the 1970s. Though historically, protein combining was promoted as a method of compensating for supposed deficiencies in vegetables as foods, studies on essential amino acid contents in plant proteins have shown that vegetarians and vegans typically do not need to complement plant proteins in each meal to reach the desired level of essential amino acids as long as their diets are varied and caloric requirements are met. The
American Dietetic Association The Academy of Nutrition and Dietetics is a 501(c)(6) trade association in the United States. With over 112,000 members, the association claims to be the largest organization of food and nutrition professionals. It has registered dietitian nut ...
and
Dietitians of Canada Dietitians of Canada (DC), or Les Diététistes du Canada in French, is the professional organization and "nation-wide voice of dietitians in Canada". As an organization DC is active at the local, provincial, national and international levels and h ...
support this position. In fact, the
American Dietetic Association The Academy of Nutrition and Dietetics is a 501(c)(6) trade association in the United States. With over 112,000 members, the association claims to be the largest organization of food and nutrition professionals. It has registered dietitian nut ...
states that complementary proteins do not need to be consumed at the same meal and plant proteins can meet all requirements. It is however indeed possible for one to develop an amino acid deficiency if they, for example, ate solely rice and in quantities limited to that necessary to meet caloric intake needs. To avoid such a deficiency, either a complementary food high in the limiting amino acid (such as legumes which are high in lysine, in the case of rice) or quantities of rice greater than that necessary to meet caloric intake needs would be required. This is not an issue when eating a varied diet. Amino acids are not stored and may be excreted sooner than complemented, under limiting conditions.


Concept

Protein nutrition is complex because any
proteinogenic amino acid Proteinogenic amino acids are amino acids that are incorporated biosynthetically into proteins during translation. The word "proteinogenic" means "protein creating". Throughout known life, there are 22 genetically encoded (proteinogenic) amino aci ...
may be the
limiting factor A limiting factor is a variable of a system that causes a noticeable change in output or another measure of a type of system. The limiting factor is in a pyramid shape of organisms going up from the producers to consumers and so on. A factor not l ...
in
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...
. Mixing
livestock feed Fodder (), also called provender (), is any agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food given to the animals (includin ...
s can optimize for growth, or minimize cost while maintaining adequate growth. Similarly,
human nutrition Human nutrition deals with the provision of essential nutrients in food that are necessary to support human life and good health. Poor nutrition is a chronic problem often linked to poverty, food security, or a poor understanding of nutritiona ...
is subject to
Liebig's law of the minimum Liebig's law of the minimum, often simply called Liebig's law or the law of the minimum, is a principle developed in agricultural science by Carl Sprengel (1840) and later popularized by Justus von Liebig. It states that growth is dictated not by t ...
: The lowest level of one of the essential amino acids will be the limiting factor in metabolism. :If the content of a single indispensable amino acid in the diet is less than the individual’s requirement, then it will limit the utilization of other amino acids and thus prevent the normal rates of synthesis even when the total nitrogen intake level is adequate. Thus the "limiting amino acid" will determine the nutritional value of the total nitrogen or protein in the diet. Plants are thus rated as protein sources by their limiting amino acids.


Examples of "limiting" amino acids in plant protein

According to WHO, human need for proteins is 0.66 g per kg of bodyweight per day. For a 70 kg person has an estimated protein requirement of 46.2g (70 kg x 0,66 g/kg). In addition, there is a specific need of essential amino acids quantities. See Essential amino acid#Recommended daily intake for a table of the values; the tables below use a percentage of the requirement. In the above examples, neither whole rice nor canned chickpeas have sufficient amounts of all required amino acids when used as the only source of 46.2 g of daily protein. The insufficient amino acid is called the "limiting" amino acid: for rice it's lysine and for chickpeas it's methionine. Consuming the specific quantity for long periods of time might result in deficiency of the amino acid. In the above example, the combination of both whole rice and canned chickpeas has no limiting amino acids, that means that only consuming rice and chickpeas, in these specific quantities of 306g/day and 261g/day respectively, for long periods of time, would not result in any of the essential amino acid deficiency, at least to the extent they are metabolized at the time. As the data of the example show, all essential amino acids are found in a specific plant, however one of them may or may not be limiting, that is, present in quantities below the WHO daily recommendation. For this reasons vegan and vegetarian diets need to be varied in terms of plants consumed.


Plant protein research

The first biochemist to enter the field was Karl Heinrich Ritthausen, a student of Justus von Liebig. Thomas Burr Osborne continued what Ritthausen started and published ''The Vegetable Proteins'' in 1909. Thus
Yale University Yale University is a Private university, private research university in New Haven, Connecticut. Established in 1701 as the Collegiate School, it is the List of Colonial Colleges, third-oldest institution of higher education in the United Sta ...
was the early center of protein nutrition, where
William Cumming Rose William Cumming Rose (April 4, 1887 – September 25, 1985) was an American biochemist and nutritionist. He discovered the amino acid threonine, and his research determined the necessity for essential amino acids in diet and the minimum daily re ...
was a student. Osborne also worked to determine the essentials, and later led the
Biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
Department at the
University of Chicago The University of Chicago (UChicago, Chicago, U of C, or UChi) is a private university, private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park, Chicago, Hyde Park neighborhood. The University of Chic ...
. When Ritthausen died in 1912, Osborne praised his efforts in biochemistry: :As a result of his later work he proved that wide differences exist between different food proteins; and he was the first to direct attention to this fact, and to discuss its probable bearing on their relative value in nutrition. Osborne then joined forces with
Lafayette Mendel Lafayette Benedict Mendel (February 5, 1872 – December 9, 1935) was an American biochemist known for his work in nutrition, with longtime collaborator Thomas B. Osborne, including the study of Vitamin A, Vitamin B, lysine and tryptophan. ...
at the
Connecticut Agricultural Experiment Station The Connecticut Agricultural Experiment Station (CAES) is the Connecticut state government's agricultural experiment station, a state government component that engages in scientific research and public outreach in agriculture and related fields. I ...
to determine the
essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life form ...
s. In the 1950s and 1960s,
Nevin S. Scrimshaw Nevin Stewart Scrimshaw (January 20, 1918 – February 8, 2013) was an American food scientist and Institute Professor emeritus at the Massachusetts Institute of Technology. Scrimshaw was born in Milwaukee, Wisconsin. During the course of hi ...
took this knowledge to
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
and Guatemala. He designed meals using local vegetables to fight against the scourge of kwashiorkor. In Guatemala he used the combination of cottonseed flour with maize, while in India he combined peanut flour with wheat.


Popularization

In 1954, Adelle Davis published ''Let's Eat Right to Keep Fit'', which described the importance of combining "incomplete" proteins to make "complete" proteins, and advised that any incomplete proteins not complemented within one hour could not be used by the body. In 1971,
Frances Moore Lappé Frances Moore Lappé (born February 10, 1944) is an American researcher and author in the area of food and democracy policy. She is the author of 19 books including the three-million-copy selling 1971 book '' Diet for a Small Planet'', which the ...
published ''
Diet for a Small Planet ''Diet for a Small Planet'' is a 1971 bestselling book by Frances Moore Lappé, the first major book to note the environmental impact of meat production as wasteful and a contributor to global food scarcity. She argued for environmental vegeta ...
'', which explained how essential amino acids might be obtained from complementary sources in vegetarian nutrition. The book became a bestseller : :An extension of a one-page handout that Lappé had circulated among her fellow improvisors in Berkeley, ''Diet for a Small Planet'' (1971) soon became ''the'' vegetarian text of the
ecology movement The environmental movement (sometimes referred to as the ecology movement), also including conservation and green politics, is a diverse philosophical, social, and political movement for addressing environmental issues. Environmentalists advoc ...
, selling in the next ten years almost two million copies in three editions and six languages. Lappé wrote: :Complementary protein combinations make for delicious recipes – they are combinations that formed the basis of the world’s traditional cuisines. We use them naturally in our cooking without even being aware of it. The three most common complementary protein combinations are: :#Grains (rice, corn, wheat, barley, etc.) + legumes (peas, beans, lentils) :#Grains and milk products :#Seeds (Sesame or sunflower) +legumes Lappé, Frances Moore (1981) ''Diet for a Small Planet'', In 1975, both
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and
American Journal of Nursing The ''American Journal of Nursing'' (AJN) is a monthly peer-reviewed nursing journal established in 1900. the editor-in-chief was Maureen Shawn Kennedy and it is published by Lippincott Williams & Wilkins. In 2009 the journal was selected as one o ...
carried articles describing the principles and practice of protein combining. For a time, The American National Research Council and the
American Dietetic Association The Academy of Nutrition and Dietetics is a 501(c)(6) trade association in the United States. With over 112,000 members, the association claims to be the largest organization of food and nutrition professionals. It has registered dietitian nut ...
(ADA) cautioned vegetarians to be sure to combine their proteins. In 1985, the principle of protein combining was explained by J. Rigó: :The biological value of proteins in general, hence also of grain-proteins, is fundamentally determined by the ratio between the essential amino acids to be found in cereals and the requirement of essential amino acids of the living creature, consuming protein...the most important way of raising the biological value ... sgiven by the technique of complementing. In 2011 PLOS ONE published an article investigating the specifics of protein combining for 1251 plant-based foods. The bases of reference are the amino acids indispensable to human nutrition, and the ideal proportioning of these amino acids in a meal. They explain, "complementation involves consuming two or more foods together to yield an amino acid pattern that is better than the sum of the two foods alone." In contrast to pairings based on food groups, such as pairing a grain with a bean, the investigators reported that pairing by food group was not supported by their work: "Examining the top 100 pairings for each food, we found no consistent pattern of food group-food group pairings."


Criticism

Protein combining has drawn criticism as an unnecessary complicating factor in
nutrition Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient ...
. In 1981,
Frances Moore Lappé Frances Moore Lappé (born February 10, 1944) is an American researcher and author in the area of food and democracy policy. She is the author of 19 books including the three-million-copy selling 1971 book '' Diet for a Small Planet'', which the ...
changed her position on protein combining from a decade prior in a revised edition of ''
Diet for a Small Planet ''Diet for a Small Planet'' is a 1971 bestselling book by Frances Moore Lappé, the first major book to note the environmental impact of meat production as wasteful and a contributor to global food scarcity. She argued for environmental vegeta ...
'' in which she wrote: :"In 1971 I stressed protein complementarity because I assumed that the only way to get enough protein ... was to create a protein as usable by the body as animal protein. In combating the myth that meat is the only way to get high-quality protein, I reinforced another myth. I gave the impression that in order to get enough protein without meat, considerable care was needed in choosing foods. Actually, it is much easier than I thought. :"With three important exceptions, there is little danger of protein deficiency in a plant food diet. The exceptions are diets very heavily dependent on
fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
or on some tubers, such as sweet potatoes or
cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names), is a woody shrub of the spurge family, Euphorbiaceae, native to South America. Although a perennial plant, cassava is extensively cultivated ...
, or on
junk food "Junk food" is a term used to describe food that is high in calories from sugar and/or fat, and possibly also sodium, but with little dietary fiber, protein, vitamins, minerals, or other important forms of nutritional value. It is also known as ...
(refined flours, sugars, and fat). Fortunately, relatively few people in the world try to survive on diets in which these foods are virtually the sole source of calories. In all other diets, if people are getting enough calories, they are virtually certain of getting enough protein." Necessity of protein combining was not asserted. Rather, the increased biological value of meals where proteins are combined was noted. In a concession, Lappé removed from the second edition "charts that indicate exact proportions of complementary proteins". The American Dietetic Association reversed itself in its 1988 position paper on vegetarianism. Suzanne Havala, the primary author of the paper, recalls the research process: :There was no basis for rotein combiningthat I could see.... I began calling around and talking to people and asking them what the justification was for saying that you had to complement proteins, and there was none. And what I got instead was some interesting insight from people who were knowledgeable and actually felt that there was probably no need to complement proteins. So we went ahead and made that change in the paper. ote: The paper was approved by peer review and by a delegation vote before becoming official. In 1994, Vernon Young and Peter Pellett published their paper that became the definitive contemporary guide to protein metabolism in humans. It also confirmed that complementing proteins at meals was totally unnecessary. Thus, people who avoid consuming animal protein do not need to be at all concerned about amino acid imbalances from the plant proteins that make up their usual diets. While many plant proteins are lower in one or more essential amino acids than animal proteins, especially lysine, and to a lesser extent methionine and threonine, eating a variety of plants can serve as a well-balanced and complete source of amino acids. Pediatrician Charles R. Attwood wrote, "The old ideas about the necessity of carefully combining vegetables at every meal to ensure the supply of essential amino acids has been totally refuted." In 2002, Dr. John McDougall wrote a correction to the American Heart Association for a 2001 publication that questioned the completeness of plant proteins, and further asserted that "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." Later that year, Dr.
Andrew Weil Andrew Thomas Weil (, born June 8, 1942) is an American celebrity doctor who advocates for alternative medicine including the 4-7-8 breathing technique. Early life and education Early years Andrew Thomas Weil was born in Philadelphia on June 8, ...
wrote that "you don’t have to worry that you won’t get enough usable protein if you don’t put together some magical combination of foods at each meal." In ''Healthy Times'' Jeff Novick wrote that the necessity of protein combining is a "myth that won’t go away". In 2005, Dr.
Joel Fuhrman Joel Fuhrman (born December 2, 1953) is an American celebrity doctor who advocates what he calls a "micronutrient-rich diet". His practice is based on his nutrition-based approach to obesity and chronic disease, also referred to as a nutritarian ...
wrote: :...plant foods have plenty of protein and you do not have to be a nutritional scientist or dietitian to figure out what to eat and you don’t need to mix and match foods to achieve protein completeness. Any combination of natural foods will supply you with adequate protein, including all eight essential amino acids as well as unessential amino acids. Dr. T. Colin Campbell wrote in 2006: :We now know that through enormously complex metabolic systems, the human body can derive all the essential amino acids from the natural variety of plant proteins that we encounter every day. It doesn’t require eating higher quantities of plant protein or meticulously planning every meal. In 2009, the
American Dietetic Association The Academy of Nutrition and Dietetics is a 501(c)(6) trade association in the United States. With over 112,000 members, the association claims to be the largest organization of food and nutrition professionals. It has registered dietitian nut ...
wrote: :Plant protein can meet protein requirements when a variety of plant foods is consumed and energy needs are met. Research indicates that an assortment of plant foods eaten over the course of a day can provide all essential amino acids and ensure adequate nitrogen retention and use in healthy adults, thus, complementary proteins do not need to be consumed at the same meal. The American Heart Association now states: :You don’t need to eat foods from animals to have enough protein in your diet. Plant proteins alone can provide enough of the essential and non-essential amino acids, as long as sources of dietary protein are varied and caloric intake is high enough to meet energy needs. Whole grains, legumes, vegetables, seeds and nuts all contain both essential and non-essential amino acids. You don’t need to consciously combine these foods (“complementary proteins”) within a given meal. Some institutions use the
Protein Digestibility Corrected Amino Acid Score Protein digestibility-corrected amino acid score (PDCAAS) is a method of evaluating the quality of a protein based on both the amino acid requirements of humans and their ability to digest it. The PDCAAS rating was adopted by the US FDA and the Fo ...
to assess diets without consideration of protein combining and hence find the use of combinations to be a challenge to their methodology. On the other hand, the site 2000KCAL.CZ asserts that any regular-sized protein source can be converted into a high-quality protein if combined with a small quantity of whey protein supplement. Without making a direct case for or against the practice of protein combining, the site challenges the notion that protein combining has to be complicated.Protein Quality and Protein Combining: Visual tools for the PDCAAS method
2000kcal.cz


References

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External links


When Your Friends Ask: "Where Do You Get Your Protein"
McDougall Newsletter
The Protein-Combining Myth
NutritionFacts.org
The Myth of Complementary Protein
Forks Over Knives
Plant-Based Protein: Requirements, Foods, Combinations
Holy Peas Nutrition Vegetarianism Proteins as nutrients