A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis.
Level 5 - mechanism / opinion, no new human data
Mechanism-based reasoning and theoretical metabolic flux modeling with no new primary human data.
PubMed 20093739 · doi:10.1007/s12038-009-0100-9
What was done
The authors conducted a theoretical stoichiometric and metabolic flux accounting analysis for an adult human. They compiled published flux estimates for all known pathways of endogenous glycine production and compared total available glycine from de novo synthesis and typical dietary intake against total metabolic demand, particularly for collagen synthesis, in a reference 70 kg human.
What was found
Synthesis from serine accounted for over 85% of total endogenous production, providing approximately 3 g/day. Total available glycine from endogenous synthesis (~3 g/day) plus typical diet (1.5–3.0 g/day) was estimated to fall short of metabolic demand by approximately 10 g/day for a 70 kg human.
Why it matters
This stoichiometric analysis suggests human endogenous synthesis of glycine is constrained and insufficient to meet total metabolic needs, supporting arguments that glycine is a conditionally essential amino acid.
Limits
The study is a theoretical calculation based on secondary literature flux estimates rather than direct human experimental measurements. It did not directly test clinical deficiency states, inter-individual metabolic variability, or in vivo compensatory adaptations.
Cited by
- supports The human body requires more than 10 grams of glycine per day but can synthesize only about 3 grams per day, resulting in a 7 to 10 gram daily glycine deficit.