Lifestyle & Belief

Science suggests MSG really isn't bad for your health after all

Monosodium_glutamate_crystals.jpg

Monosodium glutamate, popularly known as MSG, is a common food additive that has sparked a backlash for years.

Credit:

Ragesoss/Wikimedia Commons

Order from any number of Chinese takeout restaurants these days, and you may notice that many menus boast “NO ADDED MSG.” The label can also be found in supermarket aisles on snack foods or on packaged seasonings.

The labels are meant to ease consumers’ worries, because MSG, which is used as a flavor enhancer, has for decades been popularly linked to various health problems, such as headaches and allergic reactions. It's even been considered a factor in infant obesity.

“I see people all the time who are absolutely convinced that their allergic reactions are caused by MSG — it causes this, it causes that,” says allergist and immunologist Katharine Woessner of the Scripps Clinic Medical Group, who conducted a study on MSG's effects. But, she says, “I think there’s a great misunderstanding.”

Indeed, most scientists today agree that the notion that MSG causes sickness in humans is unfounded.

“It’s ridiculous,” says Ken Lee, a professor and the director of food innovation at Ohio State University. “It’s wacko, it’s weird; it’s not true that MSG has any kind of toxic or causative role in food allergies.”

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.

Most living things on earth contain glutamate, says Lee, and it’s also in many foods, including tomatoes, walnuts, pecans, Parmesan cheese, peas, mushrooms and soy sauce. An average adult consumes about 13 grams of glutamate each day from the protein in food, according to the FDA; added MSG contributes another 0.55 grams.

Monosodium glutamate was discovered more than 100 years ago by a Japanese chemist named Kikunae Ikeda, who derived it from seaweed and discovered that it had unique flavor-enhancing properties. These days, MSG is made by fermenting starch, sugar beets, sugar cane, or molasses, according to the FDA

The additive's negative reputation can be traced back to the 1960s, when The New England Journal of Medicine published a letter from a Maryland doctor named Robert Ho Man Kwok. Kwok wrote that he experienced symptoms similar to those of an allergic reaction every time he ate food from a Chinese restaurant, and he questioned the cause. Was it the wine he was drinking, the spices in the food, or the MSG? Kwok's letter — which referred to the collection of symptoms as “Chinese Restaurant Syndrome,” or CRS — prompted people to write in to the journal with their own experiences feeling flushed or getting headaches after consuming Chinese food, according to Lee.

On the heels of Kwok’s letter, a neuroscientist named John Olney published a study on MSG in Science. In his experiment, he injected the additive directly into white laboratory mice and found that the tests caused a number of neurological problems in his subjects, including brain lesions or impaired development. Taken together, Kwok’s letter and Olney’s study implicated MSG as the likely culprit behind CRS.

But there are problems relating Olney’s experiments to human subjects. He chose to inject mice with MSG under their skin, whereas the only way humans consume MSG is by eating it, says John Fernstrom, a professor of psychiatry, pharmacology and chemical biology at the University of Pittsburgh School of Medicine, and glutamate is largely metabolized in the gut. “You have to read between the lines very carefully to see when there is [a study about] MSG-induced brain damage,” says Fernstrom, “It’s always by injection.”

Furthermore, Olney injected the MSG into his mouse subjects in doses that were actually fit for horses — far higher than what any human would ever consume. “Anything consumed in excess is no good,” says Lee. “Everything consumed in excess could be toxic, including MSG. However, that being said, I have yet to see any documented account of somebody killing [himself] by consuming vast quantities of MSG. It would be extremely difficult to do.”

Subsequent experiments have helped dismantle the MSG-is-bad-for-you theory. For instance, in one study from 1993, researchers tested 71 subjects for reactions to MSG in relation to CRS, concluding that “rigorous and realistic scientific evidence linking the syndrome to MSG could not be found.”

In 1999, Katherine Woessner’s team conducted a single-blind, placebo-controlled study to test the effects of MSG on 100 asthmatic patients (an earlier paper suggested that asthmatics with a sensitivity to aspirin might be sensitive to MSG). The researchers found that, while 30 participants believed they had a history of CRS, only one showed signs of reduced lung function after exposure to MSG. When that subject was tested again — this time in a double-blind, placebo-controlled challenge — the test came out negative.

Then in 2000, researchers conducted the largest double-blind, placebo-controlled study on MSG, consisting of 130 subjects who said they were sensitive to the additive. The researchers found that MSG produced short-lasting and minor reactions in a subset of people — but these could not be reproduced consistently upon retesting. (Read about more MSG-related experiments in this peer-reviewed essay appearing in Clinical Correlations: The NYU Langone Online Journal of Medicine.)

Meanwhile, the FDA calls MSG “generally recognized as safe” (a classification that the agency originally made in 1959). On its website, the agency writes, “Although many people identify themselves as sensitive to MSG, in studies with such individuals given MSG or a placebo, scientists have not been able to consistently trigger reactions.”

So what about Chinese food? “If you think you get a reaction to Chinese food, maybe you do — it’s just not the MSG,” says Fernstrom, who is also a scientific advisor to the International Glutamate Technical Committee, which funds MSG research. “The thing is, there are all kinds of spices in Chinese food that are obviously plant-based — and people get allergic reactions to plants.”

Adds Woessner: “As humans, we like to have an explanation for things, and we have to eat every day,” so if you aren’t feeling well, she says, it’s normal to trace your steps back to the last meal you ate. But what’s important to keep in mind is, “Yes, you had that meal, yes you had those symptoms — but they're not necessarily cause and effect.”

This story first appeared as a blog post from PRI's Science Friday with Ira Flatow.