[kazinator]

That's right: "bouillon" isn't "MSG".

Some eight months ago, I reproduced these effects in myself by drinking a hot water solution of something called "Better Than Bouillon". I put about a teaspoon into a mug of hot water. On one mug per day, I was okay, but if I drank three per day, I got the headaches.

The listed ingredients of this paste are: roasted beef with concentrated beef stock, salt, hydrolyzed soy protein, sugar, corn syrup solids, flavour (dried onion and garlic, spice extracts), dried whey (milk), potato flour, caramel, corn oil, xanthan gum.

Must be the dried onion? :)

I've consumed beef, salt, corn syrup, onion, garlic, spices, whey powder, caramel, corn oil in the past in much larger amounts. Xanthan gum is just a thickener; I've used it! No problems. The only thing that stands out there is the "hydrolyzed soy protein".

[jkaplowitz]

I get that you say onion is fine for you, but it's amazing how non-obvious and common the actual culprit could be, whatever it is in your case: I have a relative who has, through trial and error, determined that tomatoes, onions, and garlic are among his migraine triggers - but shallots are fine despite being quite similar to onions. Bodies are weird. :)

[ubercore]

Have you reproduced it with MSG dissolved in water?

EDIT: Have you thought about lactose? It's in whey (depending on quality, various concentrations)

[kazinator]

Haven't tried yet. I do know I tolerate salt.

Response to EDIT: I tolerate milk products well, including cheese. I have used whey powder for supplementation (not in recent years). We're talking big quantities consumed at once. I noticed it's used in some baked goods and I tried it that way; it adds a certain milky "body" to the flavor.