This is definitely not true. There is no biological pathway that can do this. MSG is nearly identical to the glutamic acid in other foods. If it were true they'd be unable to tolerate parmesan cheese, soy sauce, aged meats, tomatoes, mushrooms, and seaweed.
There is some controversy about dietary glutamate being directly responsible for migraine. It’s common in the brain already. It’s only allowed selectively through the blood-brain barrier. However it could trigger other types of headache, and those can trigger migraines. Also, apparently more of it is formed in the brain when there are high levels of lysine and ornithine in the body. Many of the foods with high levels of glutamate also have high levels of those aminos.
High levels or low levels of sodium in the body can also be a migraine trigger. MSG is lower in sodium than table salt, but it is additional sodium. Many of the issues blamed on it though are after eating foods that contain MSG and a high amount of salt as well. That’s also true of many of the glutamate-containing foods for that matter (gravies, miso, soy sauce, aged meats).
Doctors recommend eliminating one single ingredient at a time to find your triggers. However, I’m sure many people don’t control for salt when eliminating MSG or natural food glutamate.
The number of people avoiding it is not evidence of anything other than public perception.
Elimination diets are also super impressive.
Nevertheless, it continues to give her migraines even in small portions where other foods don't. I don't doubt it could be some byproduct from the process of MSG salt's synthesis or cooking with it rather than the actual glutamic acid, or some allergy as others have suggested.
I wouldn't be so strong as to categorically say that MSG can't cause migraines in any of the human race as you so claim though. There's so much we don't know about human biological mechanisms in niche cases; even water can cause allergic reactions in certain individuals (see Aquagenic Urticaria). What is true generally is not always true specifically when it comes to human health.
To be clear: not saying you should, just wondering how you came the conclusion that those ingredients are the trigger.
I don't recommend telling people their subjective experience isn't true- you don't know for sure that they don't actually get migraines from MSG. I think it's fine to tell people that often their subjective experiences can be colored by prior knowledge, and people often ascribe causes to unrelated factors. (My personal belief is that most people who say they got a headache from MSG experienced a headache, but consuming glutamate was not the cause).
The personal, anecdotal relation seems strong on the cheese and paneer component. Even if she had something not aware that it contains either of those it would trigger a migraine, sometimes not immediately though, seems to take a few to several hours.
Will have to try a blind testing with MSG.
°In fact it was all cheeses, not just parmesan; the more aged the worse. And also chocolate, and olives. Basically anything aged or fermented. I don't know how that lines up with MSG's chemistry, but he was careful with MSG, though nothing like as avoidant as he was with soy sauce and cheese.
It's possible she believes that those items all trigger her migraines therefore her body gives her a migraine when she believes she's had one of her triggers.
A big tell would be her getting a migraine and blaming it on "hidden MSG" in a food item that doesn't have it.
Or her not getting migraine from foods that have MSG naturally but is never pointed out. Like tomatoes.
Now you’re right that MSG is more than sodium. Sodium can be a headache trigger, including migraines. Glutamate is also a migraine trigger and a fairly common one. It doesn’t happen to be one for me. However, it is a neurotransmitter that is involved in pain signaling. It’s understandable how it could easily trigger a migraine or make the pain worse.
Some triggers for some people actually help other people with migraines, like caffeine. Migraines are such an incredibly complex topic that there are medical specialists for them. Mine can be fairly debilitating, but are rare enough I don’t qualify for most prescriptions. So I definitely understand how trigger management and symptom management are a big deal.
