IN 1968 a Chinese-American physician wrote a rather lighthearted letter to The New England Journal of Medicine. He had experienced numbness, palpitations and weakness after eating in Chinese restaurants in the United States, and wondered whether the monosodium glutamate used by cooks here (and then rarely used by cooks in China) might be to blame.

The consequences for the restaurant business, the food industry and American consumers were immediate and enormous. MSG, a common flavor enhancer and preservative used since the 1950s, was tagged as a toxin, removed from commercial baby food and generally driven underground by a new movement toward natural, whole foods.

“It was a nightmare for my family,” said Jennifer Hsu, a graphic designer whose parents owned several Chinese restaurants in New York City in the 1970s. “Not because we used that much MSG  although of course we used some  but because it meant that Americans came into the restaurant with these suspicious, hostile feelings.”

Even now, after “Chinese restaurant syndrome” has been thoroughly debunked (virtually all studies since then confirm that monosodium glutamate in normal concentrations has no effect on the overwhelming majority of people), the ingredient has a stigma that will not go away.