[0] is shill work by researchers working for a MSG manufacturer. I have seen this before. One even has an "ajiusa.com" e-mail address right there, /palmface/. Can't comment on on [1]: the entire paper is paywalled as far as I can see, not even a hint at the results.
Let's try something else:
Graham TE, Sgro V, Friars D, Gibala MJ. 2000. Glutamate ingestion: the plasma and muscle free amino acid pools of resting humans. American Journal of Physiology-Endocrinology and Metabolism 278:E83–89.
These researchers provided single 150mg/kg oral doses of MSG to 9 healthy volunteers (8 males, 1 female) to determine the plasma and muscle concentrations of glutamate following ingestion. All volunteers reported transient headaches.
Shimada A, Cairns BE, Vad N, Ulriksen K, Pedersen AML, Svensson P, Baad-Hansen L. 2013. Headache and mechanical sensitization of human pericranial muscles after
repeated intake of monosodium glutamate (MSG). Journal of Headache and Pain 14:2
More than 50% of healthy, male subjects given 150mg/kg daily doses developed headaches.
>Because of the absence of proper blinding, and the inconsistency of the findings, we conclude that further studies are required to evaluate whether or not a causal relationship exists between MSG ingestion and headache.
