On April 4, 1968, a biomedical researcher wrote a letter that would forever change how America eats. In it, Robert Ho Man Kwok described a strange illness he contracted at Chinese restaurants -- specifically those that cooked with the flavoring MSG.

MSG was popular in the United States at the time. But when Kwok’s letter hit the New England Journal of Medicine, the ingredient's fortunes reversed: Consumers spurned it. Food-makers axed it. Scientists threw themselves into critical MSG research.

Fifty years later, 4 in 10 U.S. consumers still say they actively avoid MSG, according to the International Food Information Council, an industry-funded nonprofit that advocates for science in nutrition. That's despite repeat studies that have shown MSG does not produce numbness, weakness or heart palpitations, the symptoms Kwok experienced.

In hindsight, analysts say, the mania has proven both a rare glimpse into consumer biases -- and a prediction of the “clean eating” age. Many food companies now find themselves exorcising unpopular artificial or chemical ingredients, just as they did with MSG in the late 1960s and '70s. 

“That was one of the first ingredients people started getting really concerned about,” said Stephanie Mattucci, a global food science analyst at market research firm Mintel. “We’ve only seen a continuation of those fears and concerns.”

Unfortunately, when it comes to MSG, there’s a great deal of evidence that consumer fears have been misplaced.

A chemical variant of glutamate -- a substance that occurs naturally in high-umami foods, such as Parmesan cheese, walnuts, soy sauce and tomatoes -- monosodium glutamate has been widely eaten since the early 20th century, when a Japanese scientist first distilled it from seaweed.

On its own, MSG doesn’t taste like much of anything. But when added to other foods, it boosts their savoriness and overall flavor profile. That has made it popular in Asian cooking, as Kwok’s letter mentions, and in processed food products such as canned soups, frozen dinners, cold cuts, dressings and Doritos. According to the Food and Drug Administration, Americans consume roughly half a gram of MSG each day on average.

As MSG’s defenders have noted, this statistic should help show that the flavoring does not provoke the myriad symptoms that have been attributed to it. Few people claim to suffer what Kwok dubbed “Chinese restaurant syndrome” when they pop open a bag of chips.

On top of that, numerous high-quality studies of MSG have failed to demonstrate significant symptoms, even in people who claim to suffer from MSG reactions. In the 1990s, the FDA commissioned an independent review that found MSG only caused adverse effects in a small minority of “sensitive individuals” who ate large amounts on an empty stomach.

Instead, historians and researchers have blamed the initial symptoms that Kwok and others attributed to MSG on a variety of other sources: excess sodium or alcohol consumed with restaurant meals, a version of the placebo effect, growing skepticism of corporations, and deep-seated, anti-Asian prejudice.

As for the unlikely persistence of MSG-aversion, those factors are equally complicated, said Megan Meyer, the director of science communications at the International Food Information Council. 

On one hand, people tend to disbelieve scientific assertions when they contradict their personal experience, Meyer said. In other words, if you believe MSG has made you ill in the past, you are unlikely to believe research that shows it didn’t.

At the same time, IFIC's polling shows that many consumers no longer trust traditional authorities, such as the government, health-care professionals or the mainstream media, for information about what food is good or safe for them.

“The influencers that rise to the top, in our research, are friends, family and health-focused blogs and websites,” Meyer said. “I think that erosion of trust in institutions and science is not a great trajectory -- but we are clearly on it."

In some ways, Meyer and other experts see the story of MSG repeating -- and deepening -- in the current "clean-eating" trend. Where MSG was once the ingredient to banish, many big food brands are culling all chemical, artificial and genetically modified ingredients at consumers' behest.

But most of these ingredients have been used safely for decades. And many improve the nutrition and shelf life of packaged foods. Nadia Berenstein, a PhD student at the University of Pennsylvania researching the history of flavor, recently wrote that removing them is often "more about catering to a culture’s fears and biases than the genuine pursuit of better-for-you food."

“Sometimes it’s easier to put a 'free from X' label on something than to actually educate consumers about it,” said Lisa Watson, the spokeswoman for the Glutamate Association, an MSG trade group. “Personally I wish food companies would take the longer view.”

Watson says her industry is still trying to dig out from the MSG backlash, five decades later. According to Mintel, the number of new processed foods with MSG is decreasing. And sales of products advertised as “MSG-free” are expected to grow 22 percent between 2016 and 2021, according to market research firm Euromonitor.

In an effort to push back, Watson and her member companies regularly meet with chefs and nutritionists to talk up the merits of MSG. She has been heartened by statistics that show younger consumers are not quite as adverse to the product as their parents were. She has been glad to see media outlets run debunks of the MSG myth, and celebrity chefs, such as Hugh Acheson and David Chang, vocally embrace the seasoning.

The "foodie movement" also has revived interest in cooking that shows off science, said Sarah Tracy, an adjunct professor at UCLA's Institute for Society and Genetics who will publish a history of MSG this year. While Tracy isn't entirely willing to give the seasoning her seal of approval -- it is being researched for its possible role in promoting weight gain, she points out -- she sees other cooks and consumers embracing the seasoning as a sign of their culinary savviness.

Lately, Watson said, the Glutamate Association has tracked the same trend. It monitors references to MSG on social media, and they have grown more positive. Asked if the online sentiment was good overall, however, or just good compared to years past, Watson laughed.

“Let’s not put the cart before the horse,” she said. “It’s pretty clear that there are still a lot of misconceptions.”

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