Is collagen a complete protein?

The definition and the score sheet: the nine essentials, the two scoring methods, and where common proteins sit

Is collagen a complete protein is a definition question, and the honest page answers it from the definition rather than from the shelf, because complete has a precise meaning in nutrition, two scoring methods that apply it, and a position for collagen on both that is exact and unflattering, which the shelf avoids by using the word protein without the adjective. Of the twenty amino acids that human proteins are built from, the body can synthesise eleven for itself from other molecules and cannot synthesise nine, which must therefore be supplied by food and are called essential or indispensable: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. A complete protein is one that supplies all nine in at least the proportions that human protein synthesis requires, so that a person eating enough of it alone would meet their requirement for every essential amino acid; an incomplete protein is short of one or more, so that a person eating it alone, however much, would fall short of the amino acid it lacks. The scoring methods make the definition quantitative. The protein digestibility-corrected amino acid score, the method the food system used for decades, takes each essential amino acid in a protein, divides its amount by the human requirement for that amino acid, finds the lowest ratio, which belongs to the most limiting amino acid, and multiplies it by the protein's digestibility, capping the result at one, so that a protein whose least abundant essential amino acid just meets the requirement scores one and a protein whose least abundant essential falls to half the requirement scores a half. Its successor, the digestible indispensable amino acid score, does the same with better data on how well each individual amino acid is digested and absorbed and without the cap, so that proteins richer than the requirement can score above one. On either sheet the common proteins line up in an order every lifter should know. Whey, egg, milk and casein score at or near the maximum, with whey above one on the uncapped method, since none of their essential amino acids falls below the requirement and whey carries leucine at around eleven percent. Soy and meat, fish and poultry score at or near the maximum too. Wheat and rice score lower, around a half, because lysine is their limiting amino acid and falls to about half the requirement, which is why cereals are complemented by pulses. Pea protein scores moderately, limited by methionine, and the blends of pea and rice score well because their limits differ. And collagen scores zero, on both methods, which is the position the definition assigns and the sheet records.

Why collagen scores zero, what the zero does and does not mean, the roster collagen does fill, and the worked example

Collagen scores zero because its most limiting essential amino acid is not low but absent. Collagen contains no tryptophan at all, and the scoring methods, which grade a protein by its most limiting amino acid, divide zero by the requirement and return zero, whatever the protein's other amino acids are doing; the logic is not a quirk of the method but the biology it encodes, since a protein chain being synthesised that calls for tryptophan at a given position cannot be completed from a pool that collagen alone has supplied, and a person eating collagen as their only protein would, however much they ate, make no tryptophan-containing protein and would in time run short of the serotonin and niacin that tryptophan is also the precursor for. The absence is not collagen's only shortfall, though it is the one that sets the score: collagen carries around one percent leucine against whey's eleven, so that 25g delivers a quarter of a gram against the 2.5 to 3g that switches muscle protein synthesis on; it carries lysine, methionine, isoleucine and the other essentials in small amounts below the requirement's proportions; and a third of its weight is glycine with a quarter in proline and hydroxyproline, amino acids the body makes for itself and that no scoring method counts, since they are not essential. Collagen is the only protein on the supplement shelf that scores zero, gelatin being the same protein and scoring the same, and the roster with its empty seats is on the collagen protein and recovery page. What the zero means and does not mean is worth stating with care, because the shelf exploits the ambiguity in both directions. It means that collagen cannot be a person's protein: a reader cannot meet their protein requirement from collagen, cannot build or repair muscle from collagen alone and cannot count a collagen serving as the complete protein that a meal needs, and a tub that prints the register's muscle-mass sentences, lawful on any source of protein by energy, is printing them on a protein that scores zero for the purpose the sentences describe. It does not mean that collagen is useless or that its grams vanish: under the complementation rule that lets rice and beans count for each other across a day, collagen's grams join the day's pool and count as filler above a complete-protein base, on the collagen and daily protein for lifters page, and adding tryptophan to collagen lifts its score on paper without making it a muscle protein, the two meanings of complete on the make collagen complete page. And the zero says nothing about the tissues collagen is actually sold for, because those tissues keep a different roster. Connective tissue, the collagen of tendon, ligament, skin, bone and cartilage, is built from exactly the amino acids collagen carries in abundance, glycine at every third position of the helix and proline and hydroxyproline between, and the trials that found anything for collagen, the skin elasticity trials at 2.5 to 10g, the joint questionnaire trials at around 10g, the pre-loading tendon protocol at 15g and the bone density trial at 5g, were trials of substrate for connective tissue rather than of protein for muscle, which is why a protein that scores zero for completeness has a literature at all. So collagen is incomplete in a way that is precisely stated and not useless: it fails the definition of a complete protein by the absence of one essential amino acid, it is the shelf's only zero, and its roster is the connective tissue roster, for which it is sold and for which, on this site, it is stated on its true terms. The worked example is that incomplete protein stated as one: two capsules, 1200mg hydrolysed type 1 marine collagen with 12mg vitamin C at 15% of its reference value plus zinc, 120 for £16.99 at 28p a day, lab tested and UK made, a gram of protein scoring zero for completeness and sold for cartilage and bone through vitamin C's collagen formation sentence, with no muscle claim printed on it because the sheet says there should not be. Is collagen a complete protein: no, by definition and by both scores, and the zero is why it is sold for tendons, skin, joints and bone and not for muscle.

What to check on the label