Can dietary supplementation of monosodium glutamate improve the health of the elderly?

Ochanomizu University Graduate School, Tokyo, Japan.
American Journal of Clinical Nutrition (Impact Factor: 6.77). 08/2009; 90(3):844S-849S. DOI: 10.3945/ajcn.2009.27462X
Source: PubMed


Dietary free l-glutamate has been known for a century to improve taste and palatability. Recent evidence suggests that this effect is mediated through specific l-glutamate receptors located on the taste buds. However, l-glutamate receptors are also present elsewhere in the gastrointestinal tract, such as the stomach. Here, l-glutamate exerts physiologic actions beneficial to gut function by stimulating l-glutamate receptors linked to the gastric vagus nerve. In addition, dietary l-glutamate also appears to be an important energy substrate for gut tissue. Can such l-glutamate effects on taste and gut function be clinically useful? Elderly people often develop health problems related to their nutritional status that can be linked to insufficient energy and nutrient intake. A number of studies have examined the potential usefulness of l-glutamate, added to food in the form of monosodium glutamate (MSG), in promoting better nutrition in the elderly and in patients with poor nutrition. Some positive effects have been observed. This article reviews the physiologic roles of dietary l-glutamate in relation to alimentation and examines the evidence linking the utility of MSG supplementation to the improvement of nutrition in elderly and hospitalized patients.

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    • "This newly developed method for brain functional change observation in well-trained awake rats using a fMRI after nutrient stimulation in the gut by gastric intubation into the stomach was recently confirmed by c-fos expression in similar rats, suggesting that gut–brain communication through chemical senses of nutrient, particularly Glu, becomes available to research using awake animals in connection with non-invasive treatment [39, 58] due to an understanding why rats, fed a high-fat and high-sugar diet, do not become obese when Glu solution is available to drink with this food intake through higher thermogenesis due to energy expenditure. Dietary Glu and glutamine as a precursor for Glu signaling are positively promoted as a function of the alimentary tracts in infants as well as the elderly because of the biosynthesis capacity of free Glu is not sufficient in the exo- and endocrine organs [60]. "
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    ABSTRACT: Dietary glutamate (Glu) stimulates to evoke the umami taste, one of the five basic tastes, enhancing food palatability. But it is also the main gut energy source for the absorption and metabolism for each nutrient, thus, only a trace amount of Glu reaches the general circulation. Recently, we demonstrated a unique gut sensing system for free Glu (glutamate signaling). Glu is the only nutrient among amino acids, sugars and electrolytes that activates rat gastric vagal afferents from the luminal side specifically via metabotropic Glu receptors type 1 on mucosal cells releasing mucin and nitrite mono-oxide (NO), then NO stimulates serotonin (5HT) release at the enterochromaffin cell. Finally released 5HT stimulates 5HT3 receptor at the nerve end of the vagal afferent fiber. Functional magnetic resonance imaging (f-MRI, 4.7 T) analysis revealed that luminal sensing with 1 % (w/v) monosodium L-glutamate (MSG) in rat stomach activates both the medial preoptic area (body temperature controller) and the dorsomedial hypothalamus (basic metabolic regulator), resulting in diet-induced thermogenesis during mealing without changes of appetite for food. Interestingly, rats were forced to eat a high fat and high sugar diet with free access to 1 % (w/w) MSG and water in a choice paradigm and showed the strong preference for the MSG solution and subsequently, they displayed lower fat deposition, weight gain and blood leptin. On the other hand, these brain functional changes by the f-MRI signal after 60 mM MSG intubation into the stomach was abolished in the case of total vagotomized rats, suggesting that luminal glutamate signaling contributes to control digestion and thermogenesis without obesity.
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    • "GABA possesses several well-known physiological functions (i.e., anti-hypertension [3] and anti-diabetic [4]) and glutathione plays a key role in the protection of the mucosa from peroxide damage and from dietary toxins [5]. Furthermore, a number of studies have shown the possible usefulness of glutamic acid in enhancing nourishment in the elderly and in patients with poor nutrition [6,7]. At the present time, glutamic acid is largely produced through microbial fermentation because the chemical method produces a racemic mixture of glutamic acid (d- and l-glutamic acid) [8]. "
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    ABSTRACT: The oral gustatory perception during a meal has very important physiological roles such as inducing appetite, smoothing mastication and swallowing, promoting digestion and each nutrient availability. One hundred years ago, L-glutamate was discovered as a new taste substance in Japan. Since then, Japanese taste physiologists have lead the research to establish L-glutamate as the prototype molecule for the fifth basic taste (umami taste), in addition to saltiness, sweetness, bitterness and sourness. Meanwhile, various lines of evidence demonstrated that taste perception is linked to taste stimuli-oral/pharyngeal reflexes. In this review, we focus on the efficacy of L-glutamate for human salivation and discuss the possible application of umami taste simulation to the nutritional management for the elderly due to amelioration of their quality of life (QOL).
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