Last week, Allison wrote: “I recently read the NYTimes article about MSG [monosodium glutamate] and although you were quoted, I’d love to hear more of your thoughts.”

This is a tough one. My files on MSG go back to 1971 when the FDA said this flavor enhancer, the sodium salt of an amino acid that forms part of virtually all proteins, was safe for everyone “except for those who are individually sensitive to the substance.” By these, it meant people who reacted to foods containing MSG with headaches, tingling, flushing or other such neurological symptoms. Because Chinese food contained a lot of MSG, the symptoms came to be known as “Chinese Restaurant Syndrome.” In the late 1970s, scientists weighed in with reports of placebo-controlled trials that showed no reaction to MSG except for the first half hour after eating it. By 1980, scientists concluded that MSG only caused problems for a small percentage of individuals who had a genetic susceptibility. Placebo-controlled trials continue to find no difference in symptoms when people consume MSG or a placebo. That is why I told the reporter that there was no clinical evidence for problems and why “I thought the issue was settled though I know a lot of people will never believe that.” I wish what I had said next had been included because I went on to explain that such studies cannot account for the very real experience of people who experience symptoms, such as those whose letters appear in today’s Times.

How to make sense of this? MSG susceptibility falls into the category of many other food sensitivities and allergies, most of which are exceedingly difficult to diagnose. The science of food sensitivities, like much of nutrition science, is difficult to do, especially when serious symptoms are relatively rare in the population (it is too expensive to do studies on a large enough sample of individuals to get meaningful results).

If you are one of those people who experiences symptoms from MSG, there is only one thing to do: avoid it. And that brings us to the need to have more informative food labels. One again, we are in the realm of food politics.