At a dinner for foreign teachers at Tsinghua, I met a Canadian woman who teaches English literature. Soon after she moved to China, she started having nightmares every night. For dreams, they were unusually linear and realistic. They were nightmares in the sense that they felt “sinister”. This hadn’t happened to her before. It was especially puzzling because she was having a good time.
On a forum for foreigners in Beijing, she asked what might be causing the problem. MSG, she was told. All Chinese restaurants use MSG. She started cooking her own food. The problem went away. Whenever she ate a restaurant meal, the problem returned. The time between meal and sleep made a difference. The dreams would be more vivid if she slept soon after the meal.
Here is a discussion of the MSG/nightmare link with many stories about it. I believe we like the taste of MSG because glutamate is created when proteins are digested by bacteria. We like glutamate because we need to eat bacteria to be healthy. Bacteria are too big and varied to detect directly; it’s much easier to evolve a glutamate detector. The problem is that now you can have glutamate in your food without bacteria. Apparently cooked tomatoes and garlic are other sources.
With PubMed I found two relevant articles. One reported an experiment where hyperactive boys got better when additives, including MSG, were removed from their food. The other is a review article about the effects of MSG that mentions sleep.
Since the first description of the ‘Monosodium glutamate symptom complex’, originally described in 1968 as the ‘Chinese restaurant syndrome’, a number of anecdotal reports and small clinical studies of variable quality have attributed a variety of symptoms to the dietary ingestion of MSG. . . . Despite concerns raised by early reports, decades of research [this review was published in 2009] have failed to demonstrate a clear and consistent relationship between MSG ingestion and the development of these conditions..
What the woman I met did in a week or so (establish that MSG has bad effects), medical researchers — at least, judging by this review — have failed to do in 41 years (”decades of research”). Just as dermatologists have been unable to figure out that acne is caused by diet.