The difference is that those foods are high in glutamate, not the chemically-stabilised for easy human sprinkling 'monosodium glutamate'.
I've long suspected any headaches or perceived ill-effects from MSG consumption are probably just sodium spikes from dishes made with a bit too much msg and salt, perhaps washed down with some not enirely quenching alcoholic beverage.
There is a big difference between the glutamic acid in tomatoes and the refined devilry that is put in Campbell's soup, KFC chicken, and cheap asian food. I do have to watch protein powders and bars that have glutemic acid ... some of these will give me a headache (I am looking at you muscle milk).
I might be willing to try this, but I am afraid of the outcome. The headaches are violent. I have had these headaches decades and I know my triggers. MSG is the king of triggers.
