Doc - I'm not anti-MSG as I've used FAB (but I don't go out of my way to use MSG etc. when cooking at home) so I'm not disagreeing, but please correct me if I am wrong..
While L-glutamic acid (MSG) can be found naturally in the some foods and be found within the cells of the body when our bodies digestive process beaks down the acids which the body then processes, in the limited reading I've done, MSG, as used for most foods as an additive, is a chemical as it is replicated in a factory, where is acids are broken down by various processes including hydrolization, autolyzation, fermentation etc) and then refined to the final substance. This amino acid (D-glutamic acid)is slightly different structure than what is found in natually occuring L-glutamic acid. This is potentially why so manly claim or experience (where factual or not) that MSG is foods poses reactions, health problems etc.