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Division of Nutrition and Biochemical Medicine, Department of Medicine and Research Center, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand
3To whom correspondence should be addressed.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • monosodium glutamate • glutamic acid • amino acids • plasma • diet • humans
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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reported that the average daily intake of MSG in
Thai adults was 1.5 g. It has previously been shown in adults that
the ingestion of meals containing added MSG (3 g) and the consumption
of MSG (2.8 g) with meals for 5 d are not associated with Chinese
Restaurant Syndrome (Tanphaichitr et al. 1983
and 1985
).
Nonetheless, the public is still concerned about the safety of
long-term dietary MSG use. Therefore, we examined plasma glutamate
(GLU) concentrations in adult Thais identified on the basis of their
chronic use of MSG in the diet. |
SUBJECTS AND METHODS |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The strict criteria for this study were based on the definition of MSG
nonusers as individuals who had not consumed MSG regularly in their
homes for at least 1 y, and who refused to take meals outside
their homes that contained added MSG. The selection of MSG users was
straightforward. Only 10 healthy female Thai adults, aged 20–53 y, met
the nonuser criteria. They were therefore studied with another group of
10 female MSG users. Height and body weight were measured in each
subject, and the body mass index (BMI) was calculated
(Tanphaichitr 1994
).
Dietary assessment.
Dietary intakes in each subject were obtained for the 3-d period
preceding venipuncture. Daily intakes of energy, protein, fat,
carbohydrate and amino acids were then calculated for each subject with
the use of standard food composition tables (The Nutrient Data Laboratory 1997
).
Biochemical determinations.
Venous blood samples were obtained from each subject in the morning
after a 12- to 14-h fast. Plasma was separated from a heparinized
sample and used for the determination of amino acids by HPLC
(Cohen et al. 1989
) within 2 wk after storage at
-70°C. Serum was separated from a clotted sample and used to
determine total protein by biuret assay (Bender 1972
),
albumin by the bromocresol green dye-binding technique
(General Diagnostic 1974
), transferrin by the
immunochemical reaction with a specific antibody (Turbiquant,
Behringworke AG, Marburg, Germany), and retinol-binding protein
(RBP) by a single radial immunodiffusion technique (LC-Partigen,
Behringworke AG).
Statistical analysis.
Statistical analysis was performed using the SPSS for Windows Release 7.5.1 (Chicago, IL). Results were expressed as means ± SEM Comparisons were made between the two groups by a two-tailed Student’s t test. Linear and multiple regressions were used to evaluate the relative importance of the correlations among the various parameters.
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RESULTS |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The daily energy intakes of female non-MSG users and MSG users were 7150 ± 680 and 7180 ± 780 kJ (means ± SEM), respectively. Their total daily protein intakes were 51.5 ± 4.0 and 53.6 ± 4.9 g, respectively [0.97 and 1.01 g/(kg·d)], and their daily protein intakes from animal sources were 31.2 ± 4.3 and 36.9 ± 4.4 g, respectively. Daily GLU intakes (free + protein-bound) from natural sources by female non-MSG users and female MSG users were 8.50 ± 0.64 and 8.65 ± 0.71 g, respectively [160 and 162 mg/(kg·d)]. The intake of added MSG was not determined because of the assumptions and inaccuracies inherent in attempting to make such calculations.
BMI and biochemical assessment.
Table 1
shows protein-energy status in the two groups assessed by BMI and
serum protein levels including total protein, albumin, transferrin and
RBP levels. Table 2
presents fasting plasma amino acid levels.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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65.0 g/L), albumin (35.0 g/L,), transferrin (2.0 g/L) and RBP
(35 mg/dL) (Tanphaichitr 1994
). The significantly
higher serum RBP concentrations in the female MSG users, compared with
those in the female non-MSG users, however, cannot be related to a
difference in either protein or energy intakes. At present, we lack an
explanation for this difference.
The major form in which GLU is ingested in the diet is as a constituent
of protein. If our MSG users had a daily MSG intake of 1.5 g
(Pothisiri et al. 1983
) (equivalent to 1.17 g free
GLU), this amount would contribute only ~11.9% of the total daily
GLU intakes by female MSG users. Small, transient increases in plasma
GLU concentrations have been observed when MSG is ingested with meals
(Stegink 1984
, Tanphaichitr et al. 1983
).
The current data confirm that long-term MSG intake does not lead to
a chronic elevation in fasting plasma GLU concentrations (when user
values are compared with those of nonusers; see Table 2
). They suggest
further that there was no significant correlation between GLU intakes
and fasting plasma GLU concentrations. These findings are consistent
with recent studies involving intragastric infusions of isotopically
labeled glutamate, which have revealed that >90% of enteral glutamate
is catabolized by the tissues of the splanchnic bed (Battezzati et al. 1995
, Matthews et al. 1993
), largely by
the intestine (Reeds et al. 1996
).
The significantly lower plasma glutamine concentrations in the MSG
users compared with that in non-MSG users (Table 2)
could be due to
the decrease in synthesis or increase in catabolism of this amino acid
in these women.
In conclusion, these findings indicate that long-term intake of MSG is not associated with a chronic elevation of fasting plasma GLU concentrations; thus, the inference of toxicity based on assumptions of prolonged elevations in plasma glutamate is untenable. Further, these data add further indirect support to the large body of data affirming the safety of MSG for human consumption.
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FOOTNOTES |
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2 Supported by a research grant from International Glutamate Technical Committee.
4 Abbreviations used: BMI, body mass index; GLU, glutamate; MSG, monosodium glutamate; RBP, retinol-binding protein.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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1.
Battezzati A., Brillon D. J., Matthews D. E. Oxidation of glutamic acid by the splanchnic bed in humans. Am. J. Physiol. 1995;269:E269-E276
2. Bender G. T. Chemical Instrumentation: A Laboratory Manual: Based on Clinical Chemistry 1972:14-16 W..B. Saunders Co Philadelphia, PA.
3. Cohen S. A., Meys M., Tarvin T. L. The Pico 1989 Tag Method. Millipore Company Bedford, MA.
4. General Diagnostic Albustrate serum albumin reagent for manual automated analysis 1974 Warner-Lambert Morris Plains, NJ.
5.
Matthews D. E., Marano M. ., Campbell R. G. Splanchnic bed utilization of glutamine and glutamic acid in humans. Am. J. Physiol. 1993;264:E848-E854
6. Pothisiri P., Lawonprasert Y., Tanphaichitr V., Srianujata S. An investigation of apparent susceptibility of Chinese Restaurant Syndrome due to monosodium glutamate intake. Program and Abstracts of Fourth Asian Congress of Nutrition 1983:332 Saeng Printing Bangkok, Thailand abs.
7.
Reeds P. J., Burrin D. G., Jahoor F., Wykes L., Henry J., Frazer E. M. Enteral glutamate is almost completely metabolized in first-pass by the gastrointestinal tract of infant pigs. Am. J. Physiol. 1996;270:E413-E418
8. Stegink L.D. Aspartate and glutamate metabolism. Stegink L. D. Filer L. J., Jr eds. Physiology and Biochemistry 1984:47-75 Marcel Decker New York, NY.
9. Tanphaichitr V. Evaluation of nutritional status. Wahlqvist M. L. Vobecky J. S. eds. Medical Practice of Preventive Nutrition 1994:333-343 Smith-Gordon and Co., Ltd London, UK.
10. Tanphaichitr V., Srianujata S., Leelahagul P., Kulapongse S., Patchamisiri S., Pothisiri P. Effect of monosodium L-glutamate intake on protein-calorie status in healthy Thai adults. Nutr. Rep. Int. 1985;32:1073-1080
11. Tanphaichitr V., Srianujata S., Pothisiri P., Sammasut R., Kulapongse S. Postprandial responses to Thai foods with and without added monosodium L-glutamate. Nutr. Rep. Int. 1983;28:783-792
12. The Nutrient Data Laboratory (NDL) Composition of Foods: Raw Processed Prepared, USDA Nutrient Database for Standard Reference, Release No. 12 1997 Agricultural Research Service (ARS), Beltsville Human Nutrition Research Center, U.S. Department of Agriculture Beltsville, MD.
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