II. Glutamine and glutamate.
Level 5 - mechanism / opinion, no new human data
Narrative review detailing biochemical mechanisms and physiological roles without systematic methodology or original human trial data.
PubMed 12481981 · doi:10.1016/s0753-3322(02)00285-8
What was done
This paper provides a narrative review synthesizing the physiological, biochemical, and clinical roles of the glutamate family of amino acids, focusing on glutamine and glutamate in human health, metabolism, and pathological states.
What was found
The authors report that glutamine and related amino acids account for 25% of dietary amino acid intake, with glutamate comprising 11% to 22% of animal protein and up to 40% of plant protein by weight. Physiological mammalian glutamine levels are approximately 650 µmol/L. Glutamine becomes conditionally essential during severe physiological stress—including major trauma, major surgery, sepsis, bone marrow transplantation, and intensive chemo- or radiotherapy—due to consumption outpacing endogenous synthesis. The review also describes glutamine's role in ammoniagenesis, enterocyte and lymphocyte proliferation, and nitrogen balance, as well as glutamate's primary role as the main excitatory neurotransmitter in the central nervous system and precursor for GABA and glutathione.
Why it matters
It outlines the metabolic rationale for considering glutamine as conditionally essential in critical illness and highlights its central connections to energy production, antioxidant defense, and neurotransmission.
Limits
As a narrative review, it does not employ systematic search methods, quality assessment of cited studies, or quantitative meta-analysis. The abstract provides biochemical and physiological summaries rather than controlled clinical outcome data or comparative trial statistics.
Cited by
- supports Glutamine is metabolized into glutamate for cellular energy and into alpha-ketoglutarate, which serves as an energy substrate for gut cells.