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Commentary on "A dietary restriction influences the progression but not the initiation of MSG-induced nonalcoholic steatohepatitis".

Dear Editor-in-Chief: Ioffer the following critical comments on the article entitled ‘‘A dietary restriction influences the progression but not the initiation of monosodium glutamate (MSG)induced nonalcoholic steatohepatitis’’ by Fujimoto et al. The comments relate to the use of MSG in food and concern the interpretation that the authors have drawn from their results. The article focuses on the MSG-induced obesity model, which is produced by subcutaneous injection of MSG at the neonatal stage (2 mg/g body weight MSG from birth to 5 days of age, daily). The authors indicate that MSG appears to be a critical factor in the initiation of obesity, based on the result that restricted calorie intake resulted in the reduction of body weight gain but could not prevent the initiation of obesity. They also suggest the possibility that MSG used in food as an additive may be involved in the onset of obesity and that the effect of maternal MSG intake on the fetus should be considered. The MSG-induced obesity model is a well-known animal model, which was first reported by Dr. Olney in 1969. What Dr. Fujimoto et al. reported in their article is almost the same as that reported by Dr. Olney. That is, Dr. Olney reported that subcutaneous injection of MSG at the neonatal stage, daily from 1 to 10 days after birth, induced obesity at a later stage of life (up to 150 days of age) as well as fatty livers, with slightly decreased food consumption. He attributed these symptoms to brain lesions observed within a few hours after the MSG injection. The joint FAO/WHO Expert Committee on Food Additives ( JECFA) evaluated the safety of MSG rigorously in 1987, including neurotoxicity followed by endocrinological disturbance. The observed obesity is associated with an impaired pituitary function, which results in atrophy of related target organs such as thyroids and adrenals. The reduced level of prolactin and growth hormone was also reported. JECFA scrutinized the possibility that neurotoxicity might be induced by MSG and the other salts of glutamate used as food additives from various points of view, including metabolism, kinetics, nutritional aspect (intake), and long-term study. Finally, JECFA concluded that the acceptable daily intake should be not specified, because of a very low toxicity. The following are the key arguments indicating that neurotoxicity followed by obesity is not induced by MSG when used as a food additive.