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Remember Chinese Restaurant Syndrome? Diners in the ’60s developed mystery headaches, numbness, and tingling, just from eating a bit of sweet and sour chicken. It turned out taste enhancer monosodium glutamate (MSG) was the culprit. Signs began appearing in restaurant windows: NO MSG. End of story, right?

Wrong. If you think that you’re not eating MSG, take a closer look. According to former food process engineer and food scientist Carol Hoerlein and her colleagues, MSG or free glutamate, MSG’s active component, is found in an astonishing array of today’s processed and restaurant food—and even on produce.

Hoerlein’s group has compiled independent research on its nonprofit web site, MSGTruth.org. A partial list of affected foods includes some McDonald’s products, most KFC products, Hamburger Helper Microwave Singles, Doritos, Pringles, Boar’s Head cold cuts, Progresso Soups, Lipton Noodles and Sauce, Lipton instant soup mix, almost all Kraft products, all Knorr products, Cup-a-Soup, Cup-o-Noodles, soy sauce, and Worcestershire sauce (for more, see www.msgtruth.org). In addition, the EPA has approved the use of Auxigro, which contains free glutamate, as a fertilizer, so produce sprayed with Auxigro also may contain the chemical. On average, a person in an industrialized country consumes 0.3-1.0 grams of synthetic MSG a day.

The FDA classified MSG into the GRAS category (generally recognized as safe) in 1958 and has reaffirmed that position in subsequent evaluations. MSG need only be listed on the product label when synthetic MSG is added. When other ingredients containing up to 20 percent MSG are added to a product, the FDA does not require MSG to be listed. Such ingredients that may contain MSG include natural flavors, protein hydrolates, and soy protein isolate. Also, MSG produced as a result of the processing of ingredients does not need to be listed. Adding to the confusion, these products often claim to have “No MSG” or “No added MSG.”

Says Hoerlein: “I think it should be labeled properly. [The FDA] finally labeled transfats so you know what you’re eating. What the food companies are doing now is hiding it. It’s in the best interest of the food industry to say what they’re using, because a lot of people are avoiding things they don’t need to.”

Though synthetic MSG has been in use for almost a century, the question of whether it has toxic effects remains a topic of heavy debate. The glutamate lobby (www.msgfacts.com/index.html) cites studies showing MSG is completely safe, while its opponents charge that MSG (and other substances such as aspartame) are linked to the worldwide spread of obesity, exacerbation of asthma, and brain damage.

First, what is MSG? The simplest answer is that MSG is a salt composed of a sodium atom and a molecule of glutamate, a nonessential amino acid. In solid form, it is a white crystalline powder, but once it has dissolved into a liquid, its two components separate. Free glutamate is the agent that gives MSG its flavoring properties as well as its possible toxic effects.

There are many sources of free glutamate; it is released when protein is digested and occurs naturally in some foods, including breast milk, parmesan cheese, and tomatoes. Free glutamate entering the body through the gastrointestinal tract is identical and is processed identically. Glutamate is the most common amino acid in animal proteins and is a precursor for the production of other amino acids and glutathione, a compound that protects cells in the gastrointestinal tract from damage due to dietary toxins. Also, glutamate serves as an energy source for some types of muscle, including cardiac muscle.

The largest and most rigorous toxicity study involved researchers at Harvard University, Northwestern University, and UCLA. They took 130 subjects who believed that they were MSG-sensitive and exposed them to up to 5 grams of MSG a day with or without food. Twenty-four people did not complete the study, but of those who did, only two people had reactions. The symptoms these two experienced were not present when MSG was given with food. Researchers concluded that there were no reproducible responses to MSG, and that there was no evidence indicating that MSG has a toxic effect when used at levels reasonable for a food additive. In another study, human adults, infants, and premature babies were given up to 150 mg MSG per kg of body weight. Only a slight rise in plasma glutamate concentrations was produced, indicating that people of all ages can metabolize MSG efficiently.

Additional studies have shown that glutamate does not readily pass the placental barrier between mother and fetus. Pregnant rhesus monkeys were fed enough MSG to cause a ten-fold rise of glutamate in their blood levels, but little or no increase in glutamate concentration was observed in fetal blood level. Mice fed with diets containing four percent free glutamate for up to two years and including a reproductive phase did not suffer any ill effects. A two-year study in dogs fed with ten percent glutamate did not find any change in weight gain, organ weights, or general behavior.

However, large doses of MSG in newborns reproducibly cause neuronal damage in the hypothalamus of the brain. The hypothalamus is more susceptible to toxins because the blood-brain barrier surrounding it is not effective, particularly in the young. Appetite, thirst, a number of endocrine pathways, and muscle contraction are all regulated by the hypothalamus. The dose required to produce this damage is, fortunately, quite high. In very young mice, the most sensitive species, 500 mg MSG per kg body weight by average is necessary to produce neuronal damage. By contrast, the largest palatable dose for people is about 60 mg per kg body weight. Higher doses cause nausea.

These studies portray MSG as a relatively harmless flavor enhancer, but some nutritionists insist that even minute amounts of MSG can cause severe toxic reactions and cite studies conflicting with the Harvard research. A group called Truth in Labeling claims that pro-MSG studies are funded by industry advocates and that while naturally derived free glutamate has no toxic effects, synthetically produced glutamate contains toxic impurities. More alarmingly, some connect MSG, the spread of obesity, and the increase in incidence of neurological disorders.

Clinical nutritionist Carol Simontacchi writes that MSG has subtle neurological effects, including dyslexia or frequent bursts of uncontrollable anger and that, “There is evidence that MSG may be concentrated on the fetal side of the placenta so that the child receives a higher dose,” which can cause abnormal brain development. In one study, mice injected with MSG have lower free glutathione levels. Glutathione protects against mercury poisoning, a suspected cause of autism. Also, glutamate blockers are used to treat manic depression, depression, and seizures. While most evidence against MSG remains circumstantial, it is still thought-provoking.

Additional studies link glutamate to obesity and type II diabetes. According to MSGTruth.org, higher levels of glutamate in the blood can cause an increase in insulin levels that triggers hunger, and continued exposure to high insulin levels leads to insulin resistance and type II diabetes. Injection of MSG into lab animals is used to cause obesity, and these animals become resistant to leptin, a hormone secreted by fat tissue to suppress hunger. More evidence linking obesity and MSG comes from a recent study done in Germany. Young rats fed five grams of MSG a day had increased appetite, body fat percentage, and insulin resistance. However, experimental groups were small, consisting of only six to nine rats each, and the doses of MSG used were very high given that a rat weighs less than a kilogram.

Given MSG’s prevalence in our food and the conflicting studies, how does one decide what to eat or to feed children? In the end, it’s an individual choice, but that choice would be aided by proper labeling. “If you just listed on the label how much MSG is in the final product then that would help, because people are really getting fat,” says Hoerlein. “Processed foods haven’t been a blessing for humanity. We should go back to whole foods, the way we used to eat.”