Analysis: the body may fall about 10 g a day short of the glycine it needs

What they did

This is a calculation based on published research, not a new experiment. The authors had previously argued that the main route for making glycine, from another amino acid called serine, has a built-in limit. Here they compiled all the reported figures for glycine production and use in an adult human to test whether that limit leaves a shortfall.

What they found

Making glycine from serine accounted for more than 85% of the body's own glycine production. That production, about 3 g a day, plus 1.5 to 3.0 g from a typical diet, may fall significantly short of the body's total needs, including collagen production, by about 10 g a day for a 70 kg person.

The authors say this supports earlier suggestions that glycine is semi-essential, meaning the body cannot always make enough, and that it should be taken as a supplement.

What it can't tell us

This is an estimate built from other studies' figures, not a measurement of glycine shortage in real people. The size of the gap depends on the figures chosen. It does not look at cartilage, glutathione or any health outcome, and it does not test what happens when people take extra glycine.

Why it matters

Glycine is one of the three building blocks of glutathione, and in the Sekhar 2011 study older adults had much less glycine in their red cells than younger adults. This analysis offers a reason glycine might run short: the body's own production may not cover everything it is used for. It is a hypothesis about supply, not proof of a deficiency.

The paper

1. Meléndez-Hevia E, De Paz-Lugo P, Cornish-Bowden A et al. A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. J Biosci 2009.
   PMID 20093739DOI 10.1007/s12038-009-0100-9

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