Does collagen build connective tissue?

The glycine budget: the one substrate argument worth taking seriously

Does collagen build connective tissue is a question that gets two bad answers from the two sides of the shelf, the tub's yes, it is the building block, and the sceptic's no, it is just protein, and the honest page sits between them by taking seriously the one substrate argument for collagen that deserves it, because a reader who understands it understands both what collagen might do and what it cannot. The argument is the glycine budget. Collagen is around a third glycine by amino acid count, the simplest amino acid and the one that lets collagen's three chains pack into their tight helix, and the body needs glycine in large quantities every day: for synthesising its own collagen, which is a quarter to a third of all the protein in the body and turns over continuously in skin and bone; for glutathione, the main intracellular antioxidant; for creatine, which muscle uses in quantity; for bile salts, haem, purines and the detoxification of various compounds in the liver. Glycine is classed as non-essential because the body can make it, from serine mainly, and an ordinary diet supplies a few grams a day from meat, fish, dairy and pulses. The budget argument, set out in a metabolic analysis that has been widely cited and debated, adds up the body's daily glycine uses and estimates that endogenous synthesis plus an ordinary diet falls short of the total by several grams a day, perhaps ten, with the shortfall largest for collagen synthesis because collagen is where most of the body's glycine ends up; if the arithmetic is right, glycine is conditionally essential, the body is running its collagen synthesis below its potential for want of glycine, and collagen or gelatin, the richest dietary glycine sources by a wide margin, would be the natural way to close the gap, 15g of collagen supplying around 5g of glycine against the few grams in a day's ordinary protein. The honest page states the argument at full strength because it is the real reason collagen might do something that whey does not, and then states its status with the same care: the analysis is a metabolic model rather than a measurement, its assumptions about synthesis rates and requirements are contested, isotope studies of glycine flux in humans do not straightforwardly confirm a deficit in fed adults, and no outcome trial has given glycine or collagen to close the proposed gap and shown more connective tissue built as a result. It is a hypothesis with a mechanism, a plausible population in which it might matter, and no proof, which is exactly where the collagen synthesis marker trial also sits, since the doubling of a synthesis marker after 15g of gelatin with vitamin C is consistent with substrate mattering and is a marker rather than tissue.

The other half of the answer: supply builds nothing without the signal, and where the budget might be short

The other half of the answer is the one the tub leaves out, and it is the half that decides what the word build means. Connective tissue is built by cells, fibroblasts in skin, ligament and fascia, tenocytes in tendon, osteoblasts in bone, chondrocytes in cartilage, and those cells build in response to a signal, which for every load-bearing connective tissue is mechanical strain: a loaded tendon raises collagen synthesis with a peak a day later, a loaded ligament aligns its scar to the force, a loaded bone builds where strain is highest, and an unloaded tendon lowers synthesis below baseline however full the amino acid pool around it is, which is why a tendon rested in a cast loses strength in weeks while a tendon in a loading programme gains it over months, and why no quantity of glycine builds a connective tissue that nothing is asking to be built. Supply is a condition, and the signal is the cause; the glycine budget, if it is real, describes a condition that might be limiting in some people, and the loading describes the cause that is limiting in everyone who does not load. The two halves together give the honest answer to the question. Collagen supplies connective tissue's materials, glycine above all, more richly than any other food, and if the budget is short the supply may let the cells build more when they are signalled to; it builds nothing on its own, and a reader who takes it without loading has filled a pool nobody is drawing from. Where the budget might genuinely be short is the practical question, and the candidates are specific: people on low-protein diets, where glycine intake is low along with everything else; vegans, whose plant proteins are lower in glycine than animal ones, though soya and pulses supply some; periods of high collagen turnover, growth, healing from a large wound or burn, recovery from a fracture, where the pressure ulcer trials in under-nourished patients are the one place collagen improved an outcome; and perhaps heavy connective tissue loading in training, which is the pre-loading protocol's rationale. For a fed lifter eating 1.6 to 2.2g of protein per kilogram from mixed sources, the budget is least likely to be short, the signal is already present in the programme, and collagen is a modest top-up to a pool that is probably adequate, which is a fair reason to take it and not a reason to expect building. The UK register agrees with the two halves: the connective tissue sentences belong to copper, which contributes to the maintenance of normal connective tissues, and manganese, which contributes to its normal formation, the cofactors of the enzymes that do the building, and collagen holds no connective tissue sentence, since supply is not an effect. The worked example is a glycine top-up with the cofactor beside it, stated on its true terms: 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, around 400mg of glycine a day, below the 2.5 to 15g research band, carrying vitamin C's collagen formation sentence and zinc's protein synthesis sentence and no connective tissue claim. Does collagen build connective tissue: it supplies the richest glycine there is to cells that build only when loaded, and the budget argument says that supply might matter more than a sceptic allows and less than a tub claims.

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