Update February 17, 2020: In response to following the trail from the first comment below by Adrienne Samuels, I have turned around 180 degrees in my views on monosodium glutamate. See my post “The Case Against Monosodium Glutamate—Why MSG is Dangerous (as are Other Sources of Free Glutamate) and How the Dangers Have Been Covered Up.” Other than this Update, I have kept the text of what I wrote for the sake of the historical record and as a foil for what I say in post “The Case Against Monosodium Glutamate—Why MSG is Dangerous (as are Other Sources of Free Glutamate) and How the Dangers Have Been Covered Up.”

When I was in elementary school back in the 1960’s we were taught that, leaving aside the contribution of smell to taste, there were four basic tastes: salty, sweet, sour and bitter. It was late in the 20th century before I learned of the fifth basic taste: umami, which can be translated roughly as “savory.”

The Wall Street Journal article “From MSG Scare to MVP Status: How We Learned to Love Umami” by Elizabeth Dunn not only celebrates umami, but also works to rehabilitate monosodium glutamate, which heightens umami when the right amount is added. I had coded monosodium glutamate as unhealthy, but googling around shows the evidence is a lot weaker than one might think. Placebo-controlled trials at relevant dosages do not show an increase in headaches or allergy-like reactions. Moreover I found the Ken Lee’s argument in his interview with Chau Tu for the 2014 article “Is MSG Bad For Your Health?” persuasive:

Lee breaks down his reasoning: “MSG stands for monosodium glutamate. So sodium—everybody knows what that is—[is] the first ingredient in common table salt.” (Natural salt found in foods accounts for about 10 percent of a person’s total daily intake, according to the Food and Drug Administration.) Meanwhile, glutamate, the basic component of MSG, “is a synonym for glutamic acid [and] is a naturally occurring amino acid. It’s one of the building blocks of protein,” says Lee. In aqueous solutions, MSG breaks down to sodium and glutamate.

Although I have argued that concerns about ordinary table salt and the sodium it contains are overblown (“Salt Is Not the Nutritional Evil It Is Made Out to Be,” “Should the Typical Person be Restricting Salt Intake?” and “Confirmation Bias in the Interpretation of New Evidence on Salt”), I have little doubt that there exists a large enough quantity of salt consumption that it would be bad for health. Similarly, I have little doubt that that there exists a large enough quantity of glutamic acid consumption that it would be bad for health. Nevertheless, both sodium and glutamic acid are common in many ordinary foods that have been tested by time. So it would have to be hooking sodium and glutamic acid together chemically that was harmful for monosodium glutamate to be terrible. But it is hard to see why that would be so when the combination breaks apart into sodium and glutamic acid in any watery solution—such as saliva.

Even compounds that safe in food aren’t necessarily safe when injected into muscles (as monosodium glutamate often is in rat experiments) or into the brain. But Chris Mohr’s 2019 Men’s Health article “But Is MSG Bad for You? No—and Here's Why” has this reassuring passage:

In December 2018, John Fernstrom, Ph.D., professor of psychiatry and pharmacology at the University of Pittsburgh, published a study review on the supposed ill effects of MSG.

His team’s conclusion: “Findings from our data and other human studies provide important evidence that MSG in the food supply presents no hazard to the human brain. Oral ingestion of glutamate does not cross the blood brain barrier."

What is the level of harm one might worry about from glutamic acid? First, too much protein is not good, and protein is made of amino acids like glutamic acid. (See “Meat Is Amazingly Nutritious—But Is It Amazingly Nutritious for Cancer Cells, Too?”) But note that glutamic acid is not the same thing as (and is not easily converted into) the amino acid glutamine that is especially easy for cancer cells to metabolize for energy, as I discuss in “How Fasting Can Starve Cancer Cells, While Leaving Normal Cells Unharmed.”

Second, each particular amino acid probably has a variety of hormonal effects. Make these hormonal effects too strong in any one direction and it probably isn’t good.

Third, there is a genuine worry that by making unhealthy, cheap food tastier, the sodium and glutamate in MSG will lead people to eat more unhealthy, cheap food. There the principle to remember is that if food is unhealthy to begin with, sprinkling MSG on top certainly can’t transform it into healthy food! I take this point from “But Is MSG Bad for You? No—and Here's Why” where Chris Mohr reports:

“Umami is a really important factor in terms of making foods taste delish—and MSG is a concentrated form of umami,” says Ellie Krieger, R.D.N., and host of Ellie’s Real Good Food. “I think one of the biggest issues with MSG is the company it keeps—meaning the foods it’s often found in. It’s not MSG itself that’s of concern, but it can make poor-quality food taste great too so they may be more appealing than they would otherwise be.”

Umami is not all from glutamate. As Elizabeth Dunn writes in “From MSG Scare to MVP Status: How We Learned to Love Umami”:

Though the term is Japanese, umami is a global phenomenon. The same savory magic in pork and oysters runs through anchovies, seaweed and mushrooms, not to mention breast milk and amniotic fluid. In addition to glutamate, two other molecules, inosinate and guanylate, emit umami. Aging, caramelizing, drying and fermenting intensify it. Garum, the fermented fish sauce ancient Romans adored, teemed with umami, as do oyster sauce in China, miso in Japan, Worcestershire sauce in England and Maggi seasoning the world over. 

(You can learn a lot more about creating umami in the well-done Anime series “Food Wars,” which many of my family marathoned when we were together around Christmas. I recommend you do the version with subtitles. Few Anime shows have good English dubbing.)

Overall, I am willing to bet that it is safer to get the umami taste from some a reasonably balanced combination of glutamic acid, inosinate and guanylate than from an unusually large amount of glutamic acid. But glutamic acid in normal amounts seems to be part of the story of naturally occurring umami.

For annotated links to other posts on diet and health, see:

• Miles Kimball on Diet and Health: A Reader's Guide