My recollection from looking into the research myself was that though a large proportion of those who claimed MSG intolerance ended up having none, some proportion _did_ have the intolerance. The conclusion that MSG intolerance isn't real on that basis was overstated. Similarly, though many people who claim gluten intolerance have no such thing, some in fact do.
Given the nigh-infinite space of possibilities that is the human genome and the various environments and experiences of seven billion human beings, in my mind it's almost guaranteed that every human being will experience at least one medical condition that is insufficiently frequent in the population that it is "unknown to science". When your personal experience deviates from the common interpretation of scientific findings, what do you do?
I could be wrong. Maybe it's all in my head somehow? But that's a sort of real effect, too.
What I do know is that by avoiding MSG the quality of my diet has improved immeasurably, and my intestines aren't in agony. It's just an anecdote. An anecdote that happens to be my own life.
