Is Monosodium glutamate (MSG) toxic?

Monosodium glutamate (MSG) is a food additive used to flavor food such as Chinese food, soups and other food to make them tastier.

Some reports claim MSG can cause “Chinese Restaurant Syndrome” or headaches, obesity, fatigue and depression.

CONCLUSION

Claim: MSG is toxic to humans. It is poisonous, dangerous or somehow harmful to eat.

A few studies show a link to headaches, though hundreds of other studies show little to no evidence that MSG is harmful.

EVIDENCE

A Little More on MSG

MSG is a chemically modified form of glutamic acid.

What is glutamic acid? It’s a non-essential amino acid. A quick chemistry reminder, amino acids are the building blocks of protein. Protein is responsible for maintaining muscles, organs, bones and blood, among other important things. Glutamic acid is called non-essential because your body can make it, while essential amino acids come from eating foods with protein (different foods have different amino acids).

Even though your body can make it, glutamic acid is found in chicken, turkey, beef, peanut butter, salmon and much more.

So what’s the difference between glutamic acid and MSG?
In 1907, Japanese scientist Kikunae Ikeda isolated glutamate from glutamic acid and determined it was responsible for the savory, meaty taste in food with protein. Adding sodium (aka salt) to the glutamate crystallized the product and gave us monosodium glutamate or MSG.

You may have heard of the four basic tastes: sweet, sour, salty and bitter. But it turns out that many scientists now recognize this meaty taste as a fifth basic taste called umami.

What the Authorities Say

According to the Food and Drug Administration, the World Health Organization, and the Food and Agriculture Organization of the United Nations¹Walker, R., & Lupien, J. R. (2000). The safety evaluation of monosodium glutamate. The Journal of nutrition, 130(4), 1049S-1052S., MSG is a safe food ingredient.

Research

I’m not just taking their word for it. I found hundreds of MSG-related studies, papers and books. Several of them claimed some disturbing links between MSG and health issues.

Cases Against MSG

Brain Lesions, Obesity, and Other Disturbances in Mice Treated with Monosodium Glutamate²Brain Lesions, Obesity, and Other Disturbances in Mice Treated with Monosodium Glutamate
John W. Olney. Science 9 May 1969: 164 (3880), 719-721. [DOI:10.1126/science.164.3880.719] Newborn mice were injected with monosodium glutamate which caused brain lesions. As the mice grew, they showed stunted skeletal development, marked obesity, and female sterility.

Excitotoxins: The Taste That Kills³Blaycock, R. (1997). Excitotoxins–the taste that kills. Sante Fe, New Mexico: Health. A book by Dr. Russell L. Blaylock which argues that monosodium glutamate is one of several excitotoxins that causes damage to human brain cells. He claims that excitotoxins may be the cause of many degenerative diseases like Parkinson’s, Huntington’s, ALS and Alzheimer’s Disease

The toxicity/safety of processed free glutamic acid (MSG): a study in suppression of information⁴Adrienne Samuels: The Toxicity/Safety of MSG; A study in suppression of information. Accountability in Research 1999: 6(4): 259-310. This study of studies by Adrienne Samuels highlights research for the case against MSG and also calls into question some of the research that defends MSG. While not adding much medical evidence to the debate, Samuels does make a pretty good case against some of the MSG defending research, since some of the research was funded by the MSG industry.

Combination of Studies
The medical community tends to agree that our bodies are able to process natural glutamic acid, using what we need and getting rid of the excess with no side effects. Those who see MSG as harmful hypothesize that since glutamic acid is usually part of a chain of amino acids (kind of like one bead on a necklace) and monosodium glutamate is isolated or ‘free,’ our bodies rapidly absorb the latter which causes toxicity.

Digging a Little Deeper

It would take a long time to summarize and list all of the studies that found no toxic effects of MSG. Fortunately, several major organizations and independent researchers evaluated hundreds of studies and all reached the same conclusion: MSG is not toxic.⁵Walker, R., & Lupien, J. R. (2000). The safety evaluation of monosodium glutamate. The Journal of nutrition, 130(4), 1049S-1052S.⁶FASEB (1995) Analysis of Adverse Reactions to Monosodium Glutamate (MSG), Report. Life Sciences Research Office, Federation of American Societies for Experimental Biology, Washington, DC.⁷Joint FAO/WHO Expert Committee on Food Additives (1988) L-glutamic acid and its ammonium, calcium, monosodium and potassium salts. Toxicological Evaluation of Certain Food Additives and Contaminants :97-161 New York Cambridge University Press.

How do you explain the contradictory research?

A simple answer is that not all research is good. The studies where MSG caused lesions in mice used high levels of MSG that were injected rather than digested. Other studies showed that mice didn’t develop lesions when ingesting MSG and 19 out of 21 studies found primates didn’t develop lesions in either case.⁸Walker, R., & Lupien, J. R. (2000). The safety evaluation of monosodium glutamate. The Journal of nutrition, 130(4), 1049S-1052S.

Worth noting: The only 2 out of 21 studies that found lesions in primates from MSG were both completed by Olney (the same scientist who first reported the mice lesions).⁹Olney, J. W. & Sharpe, L. G. (1969) Brain lesions in an infant rhesus monkey treated with monosodium glutamate. Science (Washington DC) 166:386-388. ¹⁰Olney, J. W., Sharpe, L. G. & Fergin, R. D. (1972) Glutamate-induced brain damage in infant primates. J. Neuropathol. Exp. Neurol. 31:464-488.

Other studies found that there is little difference in how we digest natural glutamic acid and ‘free’ monosodium glutamate.¹³Burrin, D. G., & Stoll, B. (2009). Metabolic fate and function of dietary glutamate in the gut. The American journal of clinical nutrition, 90(3), 850S-856S.

The study by Samuels (the one that questioned conflicts of interest from the researchers and glutamate industry) did raise some ethical questions for studies, though she had no new or compelling evidence that MSG is harmful at normal levels when digested.

A handful of studies looked at obesity, energy, effects on the brain and other possible health issues caused by MSG. The majority of these studies showed no correlations. ¹⁴Brosnan, J. T., Drewnowski, A., & Friedman, M. I. (2014). Is there a relationship between dietary MSG obesity in animals or humans?. Amino acids,46(9), 2075-2087.¹⁵Zumin Shi, Natalie D. Luscombe-Marsh, Gary A. Wittert, Baojun Yuan, Yue Dai, Xiaoqun Pan and Anne W. Taylor (2010). Monosodium glutamate is not associated with obesity or a greater prevalence of weight gain over 5 years: findings from the Jiangsu Nutrition Study of Chinese adults. British Journal of Nutrition, 104, pp 457-463. doi:10.1017/S0007114510000760.¹⁶Geha RS, Beiser A, Ren C, et al. (2000) Review of alleged reaction to monosodium glutamate and outcome of a multicenter double-blind placebo-controlled study. The Journal of Nutrition. (4S Suppl):1058S-62S.

Headaches

There were a few that seemed to show a correlation between MSG and headaches, though these studies were not consistently repeatable and often required high doses, even without food.

Photo by Joe Green