Please see related articles and author responses: http://www.nutritionandmetabolism.com/content/9/1/50 http://www.nutritionandmetabolism.com/content/10/1/10 http://www.nutritionandmetabolism.com/content/10/1/13 ABSTRACT: The article entitled “Monosodium glutamate (MSG) intake is associated with the prevalence of metabolic syndrome in a rural Thai population”, concluded that higher amounts of individual’s MSG consumption are associated with the risk of having the metabolic syndrome and being overweight independent of other major determinants. However, this epidemiological study is the only study indicating such a relationship between MSG intake and the prevalence of metabolic syndrome and there is no direct supporting evidence for a causal relationship between MSG intake and prevalence of metabolic syndrome. This study does not indicate that MSG causes metabolic syndrome. Furthermore, there are several questionable points concerning study methods. Further carefully designed studies taking into account all glutamate sources are necessary to demonstrate the relationship between overweight, metabolic syndrome, MSG intake and umami sensitivity

Michael D Rogers

Nutrition & Metabolism

PubMed

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Rogers Nutrition & Metabolism 2013, 10:14
http://www.nutritionandmetabolism.com/content/10/1/14LETTER TO THE EDITOR Open AccessFurther studies are necessary in order to
conclude a causal association between the
consumption of monosodium L-glutamate (MSG)
and the prevalence of metabolic syndrome in the
rural Thai population
Michael D Rogers
Please see related articles and author responses:
http://www.nutritionandmetabolism.com/content/9/1/50
http://www.nutritionandmetabolism.com/content/10/1/10
http://www.nutritionandmetabolism.com/content/10/1/13Abstract
The article entitled “Monosodium glutamate (MSG) intake is associated with the prevalence of metabolic syndrome
in a rural Thai population”, concluded that higher amounts of individual’s MSG consumption are associated with
the risk of having the metabolic syndrome and being overweight independent of other major determinants.
However, this epidemiological study is the only study indicating such a relationship between MSG intake and the
prevalence of metabolic syndrome and there is no direct supporting evidence for a causal relationship between
MSG intake and prevalence of metabolic syndrome. This study does not indicate that MSG causes metabolic
syndrome. Furthermore, there are several questionable points concerning study methods. Further carefully designed
studies taking into account all glutamate sources are necessary to demonstrate the relationship between
overweight, metabolic syndrome, MSG intake and umami sensitivity.
Keywords: Monosodium glutamate, Intake, Overweight, Metabolic syndromeBackground
Recently, Insawang et al., reported that Monosodium
glutamate (MSG) intake is associated with the preva-
lence of metabolic syndrome in a rural Thai population
[1]. However, there is no supporting evidence for a
causal relationship between MSG intake and the preva-
lence of metabolic syndrome. We consider that it is pre-
mature to draw any conclusion that MSG consumption
increases the risk of metabolic syndrome and over-
weight. In this commentary, we would like to point out
some problems regarding their study and interpretation.Correspondence: michael.rogers@skynet.be
International Glutamate Technical Committee, Avenue Jules Bordet 142,
B-1140, Brussels, Belgium
© 2013 Rogers; licensee BioMed Central Ltd. T
Commons Attribution License (http://creativec
reproduction in any medium, provided the orDiscussion
The authors claim that “recent cross-sectional and longi-
tudinal studies in healthy Chinese subjects correlated
MSG intake with an increased risk of being overweight
irrespective of the total calorie intake and physical activ-
ity” and cited two articles from the same research group
that suggest an association of MSG intake and over-
weight in the Chinese population. A problem of these
studies is the large difference of MSG intake, one is only
0.33 g/day and the other is 2.2 g/day, which raises ques-
tions regarding the accuracy of the MSG intake. Further-
more, they do not mention another study that showed
no association between MSG intake and obesity in the
Chinese population [2]. In addition, a recent studyhis is an Open Access article distributed under the terms of the Creative
ommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
iginal work is properly cited.
Rogers Nutrition & Metabolism 2013, 10:14 Page 2 of 3
http://www.nutritionandmetabolism.com/content/10/1/14showing no association between MSG intake and over-
weight in the Vietnamese population was published [3].
Thus, the results of epidemiological studies on MSG in-
take and overweight are inconsistent, may be in part
because of the difficulties of assessing accurate MSG in-
take and difference in countries, population and setting.
The authors also claim that “animal models support a
causative association between obesity and neonatal or
maternal administration of high doses of MSG” and
cited four animal studies. It has been shown that when
neonatal rodents are injected with huge amounts of
MSG, blood glutamate levels becomes extremely high,
which can develop lesions in certain parts of the brain
because the blood–brain barrier in neonatal rodents is
immature, and these brain lesions resulted in obesity [4].
It has also been shown that when fasted human subjects
ingested MSG in water, consommé or a liquid meal,
blood glutamate level were transiently raised [5-7], how-
ever, the level is not high enough to develop brain
lesions and even this change did not affect the brain be-
cause, in humans, blood glutamate does not pass the
blood–brain barrier. In addition, the peak blood glutam-
ate levels could be attenuated by other food components
[8]. Thus, the circadian variation of blood glutamate
level is small during the day in humans ingesting MSG
as a food constituent [9]. The fact that the neurotoxicity
seen in neonatal rodent studies is not relevant to the
safety of MSG used as a food additive for humans has
been confirmed by authoratative risk assessment expert
bodies of the FAO/WHO, EC and USA [10].
In this study, the authors measured only the additional
MSG consumption they provided and did not take into
account other sources of glutamate. MSG is only one
among many other foods that contains glutamate. There
are two forms of glutamate in food, free and protein
bound glutamate, protein bound glutamate is digested in
the intestine to free amino acids and small peptides,
both of which are absorbed into mucosal cells where
peptides are hydrolyzed to free amino acids. Therefore,
glutamate from added MSG and free glutamate derived
from food are chemically identical and are metabolized
in the same way in humans ingesting them orally. The
human body cannot distinguish glutamate from different
sources. Glutamate rich seasonings such as fish and soy
sauce, shrimp paste, and MSG containing premix sea-
sonings, are very popular in Thailand and the total
amount of glutamate from those seasonings and espe-
cially the glutamate from proteins is usually higher than
that from MSG. It is very unlikely that exclusively the
added glutamate from MSG causes overweight and
metabolic syndrome because it is logical to assume that
glutamate from other sources also should have the same
effect. By and large, it is very unlikely that only one in-
gredient becomes the cause of obesity and metabolicsyndrome, which are complex multifactorial diseases
and this epidemiological study does not indicate MSG
causes obesity and/or metabolic syndrome. Overall,
there is a consensus that obesity is the cumulative result
of the net balance of energy intake and expenditure. In
this study, there is no association between MSG intake
and energy intake or physical activity. Thus, the possible
hypothesis that MSG makes food palatable and increases
total energy intake is not applied. Several human studies
of the elderly have demonstrated that MSG had no effect
on total energy intake and body weight, although the
effects of MSG on food intake were varied [11-13]. Thus,
there isn’t any convincing evidence for a causal relation-
ship between MSG intake and overweight or metabolic
syndrome. The BMI median and the median and per-
centage values of any of the five criteria of ATP III are
not significantly different cross-sectionally in association
with MSG intake. As a result, these data suggest a differ-
ent interpretation of the study. Recently, it was reported
that obese women have a lower MSG taste sensitivity
and prefer higher concentrations than do normal-weight
women [14]. Therefore, increased MSG intake may be,
in part, a result rather than a cause, and overweight may
be a cause rather than a result. There is the possibility
that overweight people tend to use more MSG because
of their taste preference for higher concentration and
this tendency might affect reported inconsistent associa-
tions between MSG intake and overweight. In this hy-
pothesis, the association of only MSG among other
glutamate sources seems rather convincing. Recently, it
has been suggested that glutamate or the taste of glu-
tamate, the umami taste, may play an important role in
appropriate food intake [15].
In addition, there are several questionable points
regarding the study methods as follows;
1. According to their previous study, subjects who met
exclusion criteria were excluded from the 349
subjects resulted in 315 participants [16]. Although
the exclusion criteria are the same for both studies,
participants were 349 in this study. Participants may
be the same because the median MSG intake and
interquartile range are the same for both studies,
thus, there is a discrepancy about the number of
participants.
2. They provided 250 g MSG in a box and measured
weight of returned box to assess MSG consumption
under the assumption that MSG intake measured
during 10 days reflect past MSG intake behavior.
This method seems to be similar to the weighted
food component measurement which is often used
for food consumption studies and thought to be
more accurate than other methods such as 24 h food
recall or food frequency questionnaire. However, in
Rogers Nutrition & Metabolism 2013, 10:14 Page 3 of 3
http://www.nutritionandmetabolism.com/content/10/1/14the usual weighted food component measurement,
participants use their own ingredient whereas these
participants used free MSG which was given by the
investigator in this study. This circumstance is quite
different from the usual evaluation for participants,
and possibly affected the results. If free MSG is
provided, it is very likely that individuals use more
MSG than usual because it is free. Thus, this method
could not be considered to be in the same category
as the usual weighted food component measurement
and validation information should be provided.
3. In rural areas of Thailand, multi generations are often
living together in the family home. There may be a
number of children in each such family home, but the
study excluded children under 10 years regardless of
the number of children in the calculation, and this
possibly affected the MSG consumption data, although
the statistical analysis was adjusted for age.
4. None of the median and percentage values of the five
criteria of ATP III were individually associated with
MSG intake cross-sectionally. Only the percentage of
the metabolic syndrome (defined as three or more of
the five criteria are met) is associated with MSG
intake. This seems to be an oversight. More detailed
data should be provided. In addition, the observed
associations are very weak with the very small odds
ratios for overweight and metabolic syndrome (1.16
and 1.14 respectively) although statistically significant.
5. They chose MSG users only so there is no
comparison of the non-MSG users and MSG users.
Conclusions
This epidemiological study only showed a relationship
between MSG intake and the prevalence of metabolic
syndrome and there is no direct supporting evidence for
a causal relationship. This study does not indicate that
MSG causes metabolic syndrome. Further carefully
designed studies taking into account all glutamate
sources are necessary to demonstrate the relationship
between overweight, metabolic syndrome, MSG intake
and umami sensitivity.
Competing interests
M.D.R is the Chairman of the International Glutamate Technical Committee
(IGTC), a worldwide research organization having NGO status and carrying
out or sponsoring extensive research on the efficacy, application and safety
of glutamic acid and its salts especially as used in food. IGTC receives
financial support from glutamate producers and users.
Received: 3 September 2012 Accepted: 11 January 2013
Published: 24 January 2013
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doi:10.1186/1743-7075-10-14
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conclude a causal association between the consumption of
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Further studies are necessary in order to conclude a causal association between the consumption of monosodium L-glutamate (MSG) and the prevalence of metabolic syndrome in the rural Thai population

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Further studies are necessary in order to conclude a causal association between the consumption of monosodium L-glutamate (MSG) and the prevalence of metabolic syndrome in the rural Thai population

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