Protein quality

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Protein quality is the digestibility and quantity of essential amino acids for providing the proteins in correct ratios for human consumption. There are various methods that rank the quality of different types of protein, some of which are outdated and no longer in use, or not considered as useful as they once were thought to be. The Protein Digestibility Corrected Amino Acid Score (PDCAAS), which was recommended by the Food and Agriculture Organization of the United Nations (FAO), became the industry standard in 1993. FAO has recently recommended the newer Digestible Indispensable Amino Acid Score (DIAAS) to supersede PDCAAS.

Contents

PDCAAS versus DIAAS

The main limitations of PDCAAS is that it does not take into account anti-nutrient factors like phytic acid and trypsin inhibitors, which limit the absorption of protein among other nutrients, and its use of fecal digestibility, whereas in the DIAAS system, ileal digestibility of the essential amino acids is emphasized as a more accurate measure of protein absorption. [1] [2] [3] For this reason, DIAAS is promoted as the superior method and preferable over the PDCAAS. [2] [4] Due to not factoring in anti-nutritional content into the digestibility equation, the PDCAAS has consequently been criticized for overestimating protein quality. [5] Other older methods like BV, PER, NPU and nitrogen balance may not reveal much about the amino acid profile and digestibility of the protein source in question, but can still be considered useful in that they determine other aspects of protein quality not taken into account by PDCAAS and DIAAS.

Due to the difficulties of measuring amino acid digestion through the ileum, a minimally invasive dual-tracer method has been developed for the DIAAS method. [6]

Protein sources

Protein ranking methods and standards
Protein type PER NPU BV Protein
Digestibility
(PD)
Protein
absorption
rate
Amino
Acid
Score
(AAS)
PDCAAS DIAAS Limiting
amino
acid
Complete
protein
?
Cow's milk 2.5 [1] 82% [1] 91 [1] 3.5 g/h [7] 1.0 [1] NoneYes
Whey 3.2 [1] 92% [1] 104 [1] 8–10 g/h [7] 1.0 [1] 0.9731.09 [2] [4] Histidine [8] Yes
Casein 2.5 [1] 71.2% [9] 77 [1] 94.0% [9] 6.1 g/h [7] 1.19 [10] 1.0 [1] 1.45 [9] NoneYes
Egg 3.9 [1] 94% [1] 100 [1] 97–98% [11] 1.32.8 g/h [7] 1.19 [10] 1.0 [1] 1.13 [12] NoneYes
Beef 2.9 [1] 73% [1] 80 [1] 94–98% [11] 0.94 [10] 0.92 [1] Tryptophan Yes
Oat 72, [13] 91% [10] 0.63 [10] 0.57 [14] Lysine No
Wheat 0.8 [1] 67% [1] 64 [1] 96–99% [11] 0.26, [11] 0.44 [10] 0.25–0.51 [1] [8] 0.45 [8] Lysine [8] No
Maize 1.23 [15] 85%, [13] 89% [16] 0.67 [16] Lysine [16] No
Rice 2.2 [15] 0.42 [2] 0.37 [2] LysineNo
Quinoa 75.7% [17] 82.6 [17] 91.7% [17] 0.97 [18] 0.667 [19] NoneYes
Soy 2.2 [1] 61% [1] 74 [1] 95–98% [11] 3.9 g/h [7] 0.911.0 [4] [1] [2] 0.90–0.91 [2] Meth+Cyst [8] Yes [4] [1] [2]
Black bean 0.75 [1] 0.53-0.65 [20] Meth+CystNo
Pea 88% [10] [13] 0.89 [2] 0.82 [2] Meth+CystYes
Peanut 1.8 [1] 94 [13] 0.75 [21] 0.52 [1] LysineNo
Hemp 8794.9% [14] 0.64 [14] 0.61 [14] Lysine [14] No
Mycoprotein 86% [22] 0.996 [22] Meth+CystNo
Spirulina 1.8-2.6 [15] 53–92% [15] 68 [23] 83–90%1.10 [24] LysineYes
Chlorella Meth+CystNo

Amino acid profile

The amino acid score is based on the prevalence of the essential amino acids and depends on if they reach sufficient quantity. PDCAAS scores do not take into account the quantity of the non-essential amino acids. Despite the insufficient essential amino acid profiles of most plant-based proteins, it is possible to combine low lysine with low methionine plant-based proteins, which would yield a more complete protein. [25] [1]

Below follows a table that compares the complete amino acid profiles of various proteins.

  First limiting amino acid
  Second limiting amino acid, especially depending on certain age requirements and demanding conditions for EAAs
  Amino acid is technically complete, but might turn out incomplete anyway after digestibility has been factored in
Amino acid profiles and requirements
Essential Amino AcidsRequired
per 100 g
of protein DRI [26] [27] [28] [29]
Human breast milk [30] Quinoa [31] Corn [32] Oat [33] Hemp
seeds
(shelled)
[34]
Green peas [35] Soybeans (Edamame) [36] Spirulina [37] Chlorella [38] Whey [39] Casein [40] Egg white [41]
Histidine 1.8 g2.230 g3.455 g2.710 g2.414 g2.821 g2.495 g2.756 g1.888 g3.3 g1.974 g3.2 g2.660 g
Isoleucine**2.5 g5.673 g4.279 g3.928 g4.137 g3.744 g4.547 g4.514 g5.584 g3.5 g5.001 g5.4 g6.064 g
Leucine**5.5 g9.623 g7.132 g10.597 g7.654 g6.296 g7.532 g7.334 g8.608 g6.1 g9.475 g9.5 g9.321 g
Lysine 5.1 g6.888 g6.503 g4.172 g4.179 g3.714 g7.392 g6.138 g5.264 g10.2 g8.554 g8.5 g7.394 g
Meth + Cyst 2.5 g4.052 g4.346 g2.832 g4.292 g4.672 g2.658 g2.178 g3.151 g1.6 g3.684 g3.5 g6.293 g
Phen + Tyr 4.7 g10.029 g7.302 g8.132 g8.751 g7.889 g7.332 g8.316 g9.328 g5.6 g5.790 g11.1 g10.486 g
Threonine 2.7 g4.660 g3.574 g3.928 g3.428 g3.694 g4.734 g4.087 g5.168 g2.9 g5.001 g4.2 g4.119 g
Tryptophan 0.7 g1.722 g1.418 g0.700 g1.395 g1.074 g0.863 g1.243 g1.616 g2.1 g2.106 g1.4 g1.147 g
Valine**3.2 g6.382 g5.043 g5.633 g5.585 g5.173 g5.480 g4.562 g6.111 g5.5 g5.001 g6.3 g7.422 g
Total EAAs28.7 g51.259 g43.052 g42.632 g46.014 g39.077 g43.033 g41.128 g46.718 g40.8 g46.586 g53.1 g54.906 g
Non-Essential Amino AcidsRequired? Human breast milk Quinoa Corn Oat Hemp
seeds
(shelled)
Green peas Soybeans (Edamame) Spirulina Chlorella Whey Casein Egg white
Alanine Varies3.647 g4.992 g8.983 g5.252 g4.448 g5.597 g4.609 g7.856 g7.7 g4.343 gN/A6.458 g
Arginine*4.3569.263 g3.989 g7.106 g13.245 g9.981 g8.253 g7.216 g15.8 g2.764 g3.7 g5.945 g
Asparagine*N/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/A
Aspartic acid 8.307 g9.628 g7.430 g8.632 g10.660 g11.567 g11.943 g10.080 g6.4 g9.738 gN/A11.192 g
Cysteine*N/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/A
Glutamic acid 17.018 g15.834 g19.366 g22.127 g18.249 g17.280 g19.269 g14.592 g7.8 g17.898 gN/A14.220 g
Glutamine*N/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/A
Glycine*2.634 g5.892 g3.867 g5.013 g4.690 g4.291 g4.269 g5.392 g6.2 g1.842 gN/A3.789 g
Proline*8.307 g6.563 g8.891 g5.568 g4.649 g4.034 g4.807 g4.1457.2 g5.922 gN/A3.991 g
Selenocysteine N/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/A
Serine*4.356 g4.814 g4.659 g4.471 g4.987 g4.221 g5.710 g5.2173.3 g4.606 gN/A7.321 g
Tyrosine*5.369 g2.267 g3.745 g3.409 g3.677 g2.658 g3.675 g4.496 g2.8 g2.500 gN/A4.193 g
Total non-EAAs53.994 g58.257 g60.93 g61.578 g64.605 g59.629 g62.535 g58.994 g57.2 g49.613 gN/A57.109 g
22nd Amino AcidRequired? Human breast milk Quinoa Corn Oat Hemp
seeds
(shelled)
Green peas Soybeans (Edamame) Spirulina Chlorella Whey Casein Egg white
Pyrrolysine Not used
by humans
N/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/AN/A

*Semi-essential, under certain conditions
**Branched-chain amino acid (BCAA)

Different essential amino acid requirements based on age

While the amino acid scores for PDCAAS and DIAAS are based on toddler requirements (1–3 year olds), [26] the essential amino acid requirements differ for adults and infants. [26] The most demanding essential amino acid requirements are for infants, and as children get older and transition into adulthood, the less proportions of essential amino acids they will need. This also means that many of the vegan protein sources that are limited in one or more essential amino acids, are actually less deficient in essential amino acids for adults, perhaps not deficient at all. The essential amino acid requirements for infants is based on the essential amino acid proportions in human breast milk. [26]

Essential amino acid requirements
Amino Acid required mg per g of protein Infants [26] 1–3 year olds [26] Adults (18+ y) [26]
Histidine 231817
Isoleucine 572523
Leucine 1015552
Lysine 695147
Methionine + Cysteine 382523
Phenylalanine + Tyrosine 874741
Threonine 472724
Tryptophan 1876
Valine 563229
Total mg of Essential Amino Acids per g of protein496287262

Related Research Articles

A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excreted by cells to create non-cellular structures, such as hair, scales, feathers, or exoskeletons. Some nutrients can be metabolically converted to smaller molecules in the process of releasing energy, such as for carbohydrates, lipids, proteins, and fermentation products, leading to end-products of water and carbon dioxide. All organisms require water. Essential nutrients for animals are the energy sources, some of the amino acids that are combined to create proteins, a subset of fatty acids, vitamins and certain minerals. Plants require more diverse minerals absorbed through roots, plus carbon dioxide and oxygen absorbed through leaves. Fungi live on dead or living organic matter and meet nutrient needs from their host.

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 forms, the nine amino acids humans cannot synthesize are valine, isoleucine, leucine, methionine, phenylalanine, tryptophan, threonine, histidine, and lysine.

The net protein utilization, or NPU, is the percentage of ingested nitrogen that is retained in the body. It is used to determine the nutritional efficiency of protein in the diet, that is, it is used as a measure of "protein quality" for human nutritional purposes.

<span class="mw-page-title-main">Dietary supplement</span> Product providing additional nutrients

A dietary supplement is a manufactured product intended to supplement a person's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources, or that are synthetic. The classes of nutrient compounds in supplements include vitamins, minerals, fiber, fatty acids, and amino acids. Dietary supplements can also contain substances that have not been confirmed as being essential to life, and so are not nutrients per se, but are marketed as having a beneficial biological effect, such as plant pigments or polyphenols. Animals can also be a source of supplement ingredients, such as collagen from chickens or fish for example. These are also sold individually and in combination, and may be combined with nutrient ingredients. The European Commission has also established harmonized rules to help insure that food supplements are safe and appropriately labeled.

<span class="mw-page-title-main">Mycoprotein</span> Type of single-cell fungal protein

Mycoprotein, also known as mycelium-based protein or fungal protein, is a form of single-cell protein derived from fungi for human consumption.

<span class="mw-page-title-main">Spirulina (dietary supplement)</span> Blue-green algal genus (cyanobacteria) used in food

Spirulina is a biomass of cyanobacteria that can be consumed by humans and animals. The three species are Arthrospira platensis, A. fusiformis, and A. maxima.

<span class="mw-page-title-main">Omega-6 fatty acid</span> Fatty acids where the sixth bond is double

Omega-6 fatty acids are a family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the n-6 position, that is, the sixth bond, counting from the methyl end.

Linoleic acid (LA) is an organic compound with the formula HOOC(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are cis. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 cis-9,12. A linoleate is a salt or ester of this acid.

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.

<span class="mw-page-title-main">Whole grain</span> Cereal containing endosperm, germ, and bran

A whole grain is a grain of any cereal and pseudocereal that contains the endosperm, germ, and bran, in contrast to refined grains, which retain only the endosperm.

<span class="mw-page-title-main">Amaranth grain</span> Edible grain of the Amaranth genus

Species belonging to the genus Amaranthus have been cultivated for their grains for 8,000 years. Amaranth plants are classified as pseudocereals that are grown for their edible starchy seeds, but they are not in the same botanical family as true cereals, such as wheat and rice. Amaranth species that are still used as a grain are Amaranthus caudatus L., Amaranthus cruentus L., and Amaranthus hypochondriacus L. The yield of grain amaranth is comparable to that of rice or maize.

A complete protein or whole protein is a food source of protein that contains an adequate proportion of each of the nine essential amino acids necessary in the human diet.

Biological value (BV) is a measure of the proportion of absorbed protein from a food which becomes incorporated into the proteins of the organism's body. It captures how readily the digested protein can be used in protein synthesis in the cells of the organism. Proteins are the major source of nitrogen in food. BV assumes protein is the only source of nitrogen and measures the amount of nitrogen ingested in relation to the amount which is subsequently excreted. The remainder must have been incorporated into the proteins of the organisms body. A ratio of nitrogen incorporated into the body over nitrogen absorbed gives a measure of protein "usability" – the BV.

<span class="mw-page-title-main">Protein (nutrient)</span> Nutrient for the human body

Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal per gram; in contrast, lipids provide 9 kcal per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.

Protein combining or protein complementing is a dietary theory for protein nutrition that purports to optimize the biological value of protein intake. According to the theory, vegetarian and vegan diets may provide an insufficient amount of some essential amino acids, 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. In fact, all plant foods contain all 20 essential amino acids including the 9 essential amino acids in varying amounts.

<span class="mw-page-title-main">Pea protein</span> Food product and protein supplement derived from Pisum sativum

Pea protein is a food product and protein supplement derived and extracted from yellow and green split peas, Pisum sativum. It can be used as a dietary supplement to increase an individual's protein or other nutrient intake, or as a substitute for other food products. As a powder, it is used as an ingredient in food manufacturing, such as a thickener, foaming agent, or an emulsifier.

Digestible Indispensable Amino Acid Score (DIAAS) is a protein quality method proposed in March 2013 by the Food and Agriculture Organization to replace the current protein ranking standard, the Protein Digestibility Corrected Amino Acid Score (PDCAAS).

Protein digestibility refers to how well a given protein is digested. Along with the amino acid score, protein digestibility determines the values for PDCAAS and DIAAS.

<span class="mw-page-title-main">Vegetarian and vegan dog diet</span> Adequate meat-free or animal-free nutrition

As in the human practice of veganism, vegan dog foods are those formulated with the exclusion of ingredients that contain or were processed with any part of an animal, or any animal byproduct. Vegan dog food may incorporate the use of fruits, vegetables, cereals, legumes including soya, nuts, vegetable oils, as well as any other non-animal based foods.

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