It is naturally - occurring in most foods (and Sheldon will tell you *especially* in breast milk). There's lots about it out there. Long story short: don't overuse it...
https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/monosodium-glutamate/faq-20058196
What is MSG? Is it bad for you?
Answer From Katherine Zeratsky, R.D., L.D.
"Monosodium glutamate (MSG) is a flavor enhancer commonly added to Chinese food, canned vegetables, soups and processed meats. The Food and Drug Administration (FDA) has classified MSG as a food ingredient that's "generally recognized as safe," but its use remains controversial. For this reason, when MSG is added to food, the FDA requires that it be listed on the label.
MSG has been used as a food additive for decades. Over the years, the FDA has received many anecdotal reports of adverse reactions to foods containing MSG. These reactions — known as MSG symptom complex — include:
Headache
Flushing
Sweating
Facial pressure or tightness
Numbness, tingling or burning in the face, neck and other areas
Rapid, fluttering heartbeats (heart palpitations)
Chest pain
Nausea
Weakness
However, researchers have found no definitive evidence of a link between MSG and these symptoms. Researchers acknowledge, though, that a small percentage of people may have short-term reactions to MSG. Symptoms are usually mild and don't require treatment. The only way to prevent a reaction is to avoid foods containing MSG..."
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https://health.usnews.com/health-news/blogs/eat-run/articles/2018-10-10/scientists-have-known-msg-is-safe-for-decades-why-dont-most-americans
Scientists Have Known MSG Is Safe for Decades. Why Don't Most Americans?
The ingredient is a combo of sodium and a substance found naturally in mushrooms and Parmesan cheese.
By Toby Amidor, MS, RD, CDN
Oct. 10, 2018
"MSG: You probably know it as that terrible-for-you substance in Chinese and packaged foods that many products proudly proclaim they're made without. But the truth is, MSG's bad reputation isn't deserved. In fact, studies show that the ingredient actually has nutritional benefits and adds an umami flavor to dishes.
MSG, which stands for monosodium glutamate, is simply a combination of sodium and glutamate, an amino acid that is abundant in nature and naturally present in many everyday foods like tomatoes, Parmesan cheese, mushrooms and even breast milk. The body digests the MSG seasoning and glutamates in foods the same way and cannot tell the difference between the two. So why is our understanding of the substance all off?
As a learned at a recent conference in New York City sponsored by Ajinomoto, admittedly a maker of MSG, plus my own research and knowledge as a registered dietitian, it all began with a letter to the editor of the New England Journal of Medicine in 1968 in which the author described what happened to him after eating Chinese food, including generalized weakness, palpitations and numbness in his arms. The author said that the symptoms could have been from a number of foods he ate including sodium, alcohol from the cooking wine or MSG. And yet, the letter still was enough to spur the public to associate these symptoms with a new "condition" called Chinese restaurant syndrome.
Soon enough, researchers conducted a study finding that when they injected extremely high doses of MSG directly into newborn mice's abdomens, the mice were likely to develop health issues including obesity, stunted physical development and disturbances in brain development. But despite the fact that humans aren't baby mice, nor do we consume large doses of MSG via belly injections, much the world took the results as proof that MSG is harmful. MSG was even added to the International Headache Society as a causative factor for headaches.
Fast-forward to the 1990s, and American scientists started questioning the validity of Chinese restaurant syndrome and the fear of MSG specifically in the U.S. After all, MSG can be found on many restaurant tables in China, and there were no signs of Chinese restaurant syndrome there. How could Americans be affected, yet Chinese people not be?
Over the next 30 years, American scientists conducted independent studies using validated scientific methods to better understand MSG's effects (or lack thereof). In a 1993 randomized, double-blind study published in Food Chemistry and Toxicology, for instance, researchers assigned 71 adults various amounts of MSG or a placebo over five days. Most subjects had no responses to either, and those who had been given MSG didn't experience any more "Chinese restaurant syndromes" than those who'd taken the placebo. Additional research was conducted with similar findings. Researchers concluded that Chinese restaurant syndrome isn't rooted in scientific evidence. Just this year, the International Headache Society removed MSG from its list of causative factors for headaches, and some American chefs have even started putting MSG shakers back on tables and using it in their cuisine.
Today, you can still find many brands touting "no MSG" on their labels, and suddenly embracing the ingredient may seem risky and intimidating. But if you're curious about giving it a try, I encourage it: Just a sprinkle of MSG brings out the savory deliciousness of foods and adds an umami flavor to foods like chicken broth. And, since the ingredient has two-thirds less sodium than table salt, MSG can decrease the need for salt while enhancing the flavor of the dish. Try adding just a half teaspoon of MSG to a pound of meat or four to six servings of vegetables, soup or casseroles – studies show that's enough to enhance the flavor. And after trying it myself – plain broth versus broth with a dash of MSG – I'll definitely be using it again..."
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