Adam Kuban's recent curry rice feature prompted a few commenters to fret about MSG, a phenomenon that always reminds me of the essay from Jeffrey Steingarten's collection It Must've Been Something I Ate, in which he points out that a) the Chinese, who eat MSG every day, are not suffering from debilitating headaches en masse, and b) foods like Parmesan cheese and ketchup contain enough free glutamate to trigger headaches in people who say they're affected by MSG but no one ever complains about them.
The Guardian's Alex Renton wrote a great article two years ago about the mythology of MSG that goes from the discovery of umami, to the mass production of MSG, to the 1968 article that triggered the spurious conflation of MSG with Chinese Restaurant Syndrome. From the piece: "Science has still not found a convincing explanation for CRS: indeed, some researchers suggest it may well be to do with the other things diners have imbibed there - peanuts, shellfish, large amounts of lager. Others say that fear of MSG is a form of mass psychosis - you suffer the symptoms you've been told to worry about." Renton himself experiments with the stuff, to hilarious results.