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  • Letter to the Editor
  • Published:

No consensus on glutamate

European Journal of Clinical Nutrition volume 62, pages 1252–1253 (2008)Cite this article

Sir, with irritation I took notice of the consensus meeting paper, ‘monosodium glutamate – an update’, by Beyreuther et al., published in Eur J Clin Nutr, 2006. The authors conclude, ‘a maximum (GLU) intake of 16.000 (sixteen dot triple zero) mg/kg body weight is regarded safe’. The number is misleading. It might be interpreted as 16 mg/kg body weight or 16 000 mg/kg, that is 16 g/kg body weight. Reading the manuscript itself, the confusion increases. When addressing the question, ‘can we define a safe level of intake regarding adding GLU?’ the authors state, ‘based on dietary animal studies (metabolic control), a ‘no observed adverse effect level’ of 16000 mg/kg body weight was calculated in weaning animals …’. Yet, on page 7, evidence is cited that ‘the oral dose that is lethal to 50% of subjects (LD50) in rats and mice is 15 000–18 000 mg/kg bw, respectively’. This is difficult to understand.

Even when disregarding misprints, the consensus paper is far from being a consensus. In 1995, Monno et al. (1995) studied the effect of high doses of monosodium glutamate (MSG) on the extracellular concentration of glutamate (GLU) in the hypothalamus and in the hippocampus of freely moving rats. MSG at 4 g/kg (40% solution) given by gavage caused a significant increase in plasma (5.3±0.4-fold, P<0.01) and extracellular GLU in the hippocampus (4.2±0.6-fold, P<0.01) and in the hypothalamus (8.9±1.7-fold, P<0.01) compared to control rats receiving a 40% sucrose solution (10 ml/kg). The peak increase was found within 40 min after MSG administration, then declining to baseline in the next 80 min. In 1995, Currie et al. (1995) examined paraventricular nucleus extracellular amino-acid concentrations in awake, freely behaving rats following gavage of equicaloric loads of a balanced amino-acid mixture, glucose (0.89 g) or water. Dialysate levels of GLU, isoleucine, leucine, methionine, threonine, tyrosine and valine showed reliable increases after amino-acid treatment. The authors concluded that specific brain regions may respond uniquely to amino-acid ingestion and further imply that dietary composition may influence the amino-acid profiles of the extracellular fluid in brain.

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  1. University of Kiel Germany, Altenhof, Germany. E-mail: hermanussen.aschauhof@t-online.de,

    M Hermanussen

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Hermanussen, M. No consensus on glutamate. Eur J Clin Nutr 62, 1252–1253 (2008). https://doi.org/10.1038/sj.ejcn.1602828

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