Is Monosodium Glutamate (MSG) bad?

Injections are bad (please don't inject MSG) and can be used as a mouse model of obesity if injected into the brain, but oral consumption of MSG doesn't seem harmful in moderation. There is some validity to the claim of people having MSG-induced headaches


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What does MSG do?

Practical Usage

Monosodium Glutamate (MSG) is a flavor enhancer commonly used to enhance the flavor of umami, which is savory or meaty flavors.[1] Persons with a preference for dietary protein[2] or with repeated exposure to MSG[3] also appear to be more receptive (taste-wise) to the addition of MSG, while MSG increases subjective rating scores of 'meatiness' of a meal.[2]

It is thought to contribute to the obesity epidemic due to its association with obese persons,[4] although this data has been called into question,[5] and due to injections of MSG into newborn rats being able to induce obesity later in life due to disrupting caloric regulation.[6]

Causes food to possess a meaty/meatier taste, associated with obese persons (causation not established) and thought to contribute to obesity due to MSG being used in a research model to induce obesity in newborn rats (via injection)

Mechanisms

MSG appears to be one of the more potent (yet not necessarily adverse) stimulators of salivation; citric acid can outperform MSG on a weight basis but may not be consumed in as high doses.[7] The mechanism of enhanced sensation of meat, however, may be due to MSG acting on similar receptors as some peptides (which are components of meat) suggesting the mGlu4a receptor may induce the sense of umami.[8]

It may raise plasma glutamate levels, and in adult men consuming 75mg/kg and 150mg/kg this has been recorded to be elevated by 375% or 556%, respectively.[9] Another study using 150mg/kg bodyweight MSG noted increased plasma glutamate measured at 18-fold when ingested and compared to resting subjects, but this difference was attenuated during exercise;[10] exercise normally increases glutamate (in this study, to 470+/-52uM) while the increase seen in MSG combined with exercise was 630+/-63uM (134% of placebo).[10] MSG also appeared to increase circulating levels of Taurine, alanine, and aspartate which paralleled the circulating levels of glutamate, and a slow but steady increase in Glutamine thought to be from conversion from glutamate.[10]

May stimulate glutamate receptors where MSG reaches (such as the tongue) and may also increase circulating glutamate levels after oral ingestion, although other amino acids are increased


Interventions

A few blinded interventions have been conducted with MSG. It should be noted that blinding is both desired due to the social perception of MSG being 'bad', yet difficult due to the unique sensory properties of MSG; many studies attempt to mimic the taste of MSG with NaCl or inosine monophosphate-5, another umami flavoring.[11]

Food Intake and Body Weight

As pertaining to issues with body weight, MSG (1.2g) appears to reduce appetite and hunger for up to 210 minutes after consumption when added to chicken broth (double-blind study) yet did not reduce subsequent food intake; did not increase either.[12] This study also noted that the addition of added fats was successful in reducing subsequent food intake, but conferred added calories.[12] Another study in 22 persons pairing MSG with a high protein meal also noted that the addition of MSG did not further suppress appetite or measured biomarkers (insulin, GLP-1) any more than the high protein meal itself, but increased food intake slightly (0.64+/-0.2 MJ, which is 152.8 calories).[13]

Other studies measuring food intake as a secondary outcome may also note increased food intake associated with MSG, even when blinded.[1] However, these are countered with other studies failing to note increases in energy intake overall.[14]

At least one study looking at food preferences noted a shift towards starch products, and less yogurt and lemon juice; suggesting food availability may play a role.[14]

Does not appear to significantly influence appetite or hunger in any way, but it has been reported to increase food intake when blinded although this is inconsistent. Neither the possibility of nutrient partitioning (eating more starches) or the possibility of making food more delicious cannot be refuted at this time due to lack of evidence

Limited studies are conducted on MSG for a prolonged period of time, but this study over 16 weeks in a nursing home (where food intake is easily measured) noted that the addition of 300mg MSG daily was not associated with an increase in food intake or weight at the end of the study.[15]

Adverse Symptoms

In regards to headaches, a study with 14 health men consuming 75mg/kg or 150mg/kg bodyweight MSG that was blinded was able to find a significant increase in headache frequency in the MSG group, which may have been due to the increase in systolic blood pressure observed (diastolic and heart rate unaffected) during 2 hours after consumption or the increase in plasma glutamate.[9] Although no men reported headaches when they consumed the drink laced with salt (NaCl), four reported headaches at 75mg/kg (the lower dose) and and only one at 150mg/kg. On a subjective scale of 1-10, the headaches were rated 1, 1, 4, and 4 for the lower dose and 3.5 for the higher dose.[9] A later study (with a larger sample of 130) noted that there was indeed an association (of 'general symptoms' of which headache/cerebral blood pressure was a major one) that held when blinded, where people who self-reported as being sensitive to MSG were more likely to report side effects with 5g of MSG relative to placebo[16] and these results have been replicated elsewhere.[17] The former study did note, however, that there was inconsistency with repeated trials, and no significant side-effects were seen.[16] The symptoms reported appear to be related mostly to fatigue, muscle tightness or cramping, and headaches.[17][16]

Limited evidence exists, but it supports the existence of the 'MSG symptom complex' (also known as the Chinese Restaurant Syndrome) and supports the association between people who self-report sensitivity to MSG and actually experiencing the effects


Possible Benefits?

One study that induced intestinal lesions in rats with the use NSAID drug overdose noted that giving the rats MSG in their food supply (at 5%) after the lesion was induced prevented the NSAID drug from impairing recovery rate.[18] These protective effects have been replicated in vitro (outside of a living body)[19][20] and an improved intestinal defense against acids (from inducing secretion of sodium bicarbonate) was noted.

The currently hypothesized mechanism is that MSG is negating the enterobacterium invasion that precedes NSAID-induced ulcers and lesions, thus hindering the pro-inflammatory actions of the bacteria to almost the level of control.[18]

Moderate to high doses may exert protective effects against NSAID-induced intestinal damage


MSG-Obese Rat Model?

The MSG-Obese rat model (sometimes also called glutamate-obese) is an animal model where neonatal mice or rats are injected with MSG into their brains. This technique damages monoamine metabolism in the brain acutely[21] which prolongs until the adult life and may cause increased food intake in rats.[22] Even independent of food intake, impairment to the thyroid gland and its hormones also occur in adult rats to a small degree[23][24] and impair growth hormone fluctuations as well.[25][26] These effects are due to injections of MSG into the brain inducing a excitotoxic reaction, and destroying the ventromedial nucleus[27] and arcuate nucleus[28] in the hypothalamus and permanent hormonal and nerve damage.

This is a rat model mainly used to study obesity as it pertains to catecholamines (dopamine, adrenaline) or deficiencies in other monoamines (serotonin); deficiencies of which are sometimes seen in humans who are obese.

There is no evidence currently that oral administration of MSG can induce these effects in adult animals, despite the reliability of intracerebral injections to neonatal rats in doing so.


Overall

Injecting MSG is unsafe. Especially when injected directly into the brain.

While it would be incorrect to state MSG as being proven safe, it would be equally incorrect to state that MSG is unsafe. Provided you do not feel any side-effects, MSG consumption is likely safe for you.

Tags: MSG, monosodium, glutamate, glutamine, sodium, chinese, restaurant, syndrome, headache

  1. Yeomans MR, et al. Acquired flavor acceptance and intake facilitated by monosodium glutamate in humans. Physiol Behav. (2008)
  2. Luscombe-Marsh ND, Smeets AJ, Westerterp-Plantenga MS. Taste sensitivity for monosodium glutamate and an increased liking of dietary protein. Br J Nutr. (2008)
  3. Kobayashi C, Kennedy LM. Experience-induced changes in taste identification of monosodium glutamate. Physiol Behav. (2002)
  4. He K, et al. Consumption of monosodium glutamate in relation to incidence of overweight in Chinese adults: China Health and Nutrition Survey (CHNS). Am J Clin Nutr. (2011)
  5. Bursey RG, Watson L, Smriga M. A lack of epidemiologic evidence to link consumption of monosodium L-glutamate and obesity in China. Am J Clin Nutr. (2011)
  6. Kanarek RB, et al. Juvenile-onset obesity and deficits in caloric regulation in MSG-treated rats. Pharmacol Biochem Behav. (1979)
  7. Hodson NA, Linden RW. The effect of monosodium glutamate on parotid salivary flow in comparison to the response to representatives of the other four basic tastes. Physiol Behav. (2006)
  8. Monastyrskaia K, et al. Effect of the umami peptides on the ligand binding and function of rat mGlu4a receptor might implicate this receptor in the monosodium glutamate taste transduction. Br J Pharmacol. (1999)
  9. Baad-Hansen L, et al. Effect of systemic monosodium glutamate (MSG) on headache and pericranial muscle sensitivity. Cephalalgia. (2010)
  10. Mourtzakis M, Graham TE. Glutamate ingestion and its effects at rest and during exercise in humans. J Appl Physiol. (2002)
  11. Wifall TC, et al. An analysis of 5'-inosine and 5'-guanosine monophosphate taste in rats. Chem Senses. (2007)
  12. Carter BE, et al. Supplementing chicken broth with monosodium glutamate reduces hunger and desire to snack but does not affect energy intake in women. Br J Nutr. (2011)
  13. Luscombe-Marsh ND, Smeets AJ, Westerterp-Plantenga MS. The addition of monosodium glutamate and inosine monophosphate-5 to high-protein meals: effects on satiety, and energy and macronutrient intakes. Br J Nutr. (2009)
  14. Bellisle F, et al. Monosodium glutamate affects mealtime food selection in diabetic patients. Appetite. (1996)
  15. Essed NH, et al. No effect of 16 weeks flavor enhancement on dietary intake and nutritional status of nursing home elderly. Appetite. (2007)
  16. Geha RS, et al. Multicenter, double-blind, placebo-controlled, multiple-challenge evaluation of reported reactions to monosodium glutamate. J Allergy Clin Immunol. (2000)
  17. Yang WH, et al. The monosodium glutamate symptom complex: assessment in a double-blind, placebo-controlled, randomized study. J Allergy Clin Immunol. (1997)
  18. Amagase K, et al. New therapeutic strategy for amino acid medicine: prophylactic and healing promoting effect of monosodium glutamate against NSAID-induced enteropathy. J Pharmacol Sci. (2012)
  19. Akiba Y, et al. Luminal L-glutamate enhances duodenal mucosal defense mechanisms via multiple glutamate receptors in rats. Am J Physiol Gastrointest Liver Physiol. (2009)
  20. Akiba Y, Kaunitz JD. Duodenal chemosensing and mucosal defenses. Digestion. (2011)
  21. Johnston CA, Tesone M, Negro-Vilar A. Steroid-monoamine feedback interactions in discrete brain regions using as a model the monosodium glutamate (MSG)-lesioned rat. Life Sci. (1984)
  22. Nakagawa T, et al. Effects of chronic administration of sibutramine on body weight, food intake and motor activity in neonatally monosodium glutamate-treated obese female rats: relationship of antiobesity effect with monoamines. Exp Anim. (2000)
  23. Miskowiak B, Partyka M. Effect of neonatal treatment with MSG (monosodium glutamate) on thyroid of the adult male rats. Histol Histopathol. (1999)
  24. Miśkowiak B, Partyka M. Effects of neonatal treatment with MSG (monosodium glutamate) on hypothalamo-pituitary-thyroid axis in adult male rats. Histol Histopathol. (1993)
  25. Maiter D, et al. Neonatal treatment with monosodium glutamate: effects of prolonged growth hormone (GH)-releasing hormone deficiency on pulsatile GH secretion and growth in female rats. Endocrinology. (1991)
  26. Millard WJ, et al. Evidence that reduced growth hormone secretion observed in monosodium glutamate-treated rats is the result of a deficiency in growth hormone-releasing factor. Endocrinology. (1982)
  27. Zhang WM, Kuchár S, Mozes S. Body fat and RNA content of the VMH cells in rats neonatally treated with monosodium glutamate. Brain Res Bull. (1994)
  28. Nemeroff CB, et al. Growth, endocrinological and behavioral deficits after monosodium L-glutamate in the neonatal rat: possible involvement of arcuate dopamine neuron damage. Psychoneuroendocrinology. (1977)

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