Critics charge that MSG causes diabetes, headaches, or obesity. But are these claims true?
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This is the second in a two-part article on monosodium glutamate, or MSG. As I discussed last week, MSG is an ingredient made of salt and the amino acid glutamate that’s used to enhance the flavor of foods. The reason it has this effect is that your tongue has special flavor receptors that respond specifically to glutamate. Glutamate is found naturally in foods like parmesan cheese and tomato juice and has several important functions in the body—including acting as a neurotransmitter in the brain.
The U.S. Food and Drug Administration, as well as various international food safety and health agencies, consider MSG to be perfectly safe when used as a food additive or flavor enhancer. In fact, adding a little MSG can help manufacturers reduce the sodium in processed foods without sacrificing flavor.
However, a lot of people charge that MSG is not harmless—causing headaches, flushing, and other temporary but unpleasant reactions in people who are sensitive to it. There are also concerns that it may cause neurological damage, diabetes, or even be linked to the obesity epidemic. Today, I want to take a closer look at the evidence used to support these charges.
Does MSG Cause Neurological Damage?
Concerns about the effects of MSG on the brain appear to stem from an early experiment in which researchers injected newborn mice with very large amounts of MSG. The mice developed brain lesions. That’s never a good sign. Of course, the experiment was not repeated on humans but based on this preliminary data, I feel very comfortable concluding that we should not inject huge doses of MSG into babies—or adults for that matter.
However, when MSG is consumed as part of the diet—even at levels hundreds of times above normal consumption patterns—it does not appear to cause brain lesions or any other neurological changes in mice or any other animals that they’ve tried it on, including humans.
Because glutamate acts as a neurotransmitter, it might seem logical that eating large amounts of it could flood your brain with too much of a good thing. However, your brain is protected from this and other indiscretions by something known as the “blood-brain barrier,” a sort of filter that prevents compounds in your blood (such as glutamate) from crossing into your brain.
In other words, the levels of glutamate in your brain stay fairly constant regardless of how much or how little glutamate or MSG you consume. That’s why it’s unlikely that dietary MSG would have any direct effect on brain function.
Does MSG Cause Diabetes?
OK, so maybe the “blood-brain barrier” protects the brain from the effects of MSG. But what about all the organs below your neck? For example, one study found that when they gave people large doses of free glutamate (about 20 times the average amount consumed over the course of an entire day), their insulin levels tripled. That could certainly be a problem. High insulin levels are an early warning sign for Type 2 diabetes.
However, taking 20 days’ worth of glutamate in capsule form on an empty stomach is a rather unusual scenario. First of all, you’d be hard pressed to find foods with that much MSG in them. One of the properties of MSG is that its flavor enhancing effect maxes out at a fairly low dose. Adding more MSG doesn’t further enhance the flavor or enjoyment of foods and manufacturers are pretty unlikely to spend money adding stuff for no reason. And secondly, because MSG’s only function is to enhance the flavor of food, it’s extremely unlikely that you’d be consuming large amounts of it as a supplement, without any food.
And in fact, when researchers did the same experiment under slightly more realistic conditions—that is, people were still given very large amounts of glutamate, but with a meal—they did not get the same results. Insulin levels were only slightly higher in the subjects who were given the glutamate than in the subjects who ate the meal with no glutamate.
Apparently, glutamate receptors on the tongue signal the body that food is on the way, stimulating the release of insulin in preparation for an impending rise in blood sugar. It would seem that this would only be a problem if no food is on the way. So, please refrain from taking large doses of MSG in capsule form on an empty stomach and I think you’ll be OK.
Does MSG Cause Obesity?
Some surveys have found that people who use MSG are more likely to be obese than those who do not; while other polls failed to find a link. But statistical correlations like this one are extremely hard to draw any conclusions from. Does consuming MSG affect your hormones in ways that cause you to gain weight? Or is it simply that the junk foods and snack foods that supply so many surplus calories are also likely to be high in MSG? If you took MSG out of the diet and left everything else the same, would it make any difference?
Due to a lack of solid evidence, I’m afraid all I can offer is an educated guess: I’ll bet that a high-calorie diet of MSG-free junk food is just as likely to lead to weight gain as one with MSG. Conversely, a generally healthy diet containing moderate amounts of MSG is unlikely to make you obese. Even if MSG does have some sort of unique obesity-promoting action, it’s going to have to get in line behind sedentary lifestyles, excessive consumption of refined sugars, and the ubiquity of cheap, high calorie food as a leading cause of obesity.
Does MSG Cause Headaches?
Finally, let’s tackle the least scary—but most common—charge against MSG: that it causes headaches, flushing, tingling, or other symptoms originally referred to as “Chinese Restaurant Syndrome” and now more sensitively referred to as “MSG Symptom Complex.” Symptoms are said to occur within 30 to 60 minutes of eating foods containing MSG, resolving after an hour or so with no lasting effects. Some people also say that MSG triggers migraines.
However, there have been a slew of interesting studies that suggest (pretty strongly) that whatever might be causing these symptoms—it’s not the MSG. In double-blind, placebo controlled trials, people who identify themselves as being highly sensitive to MSG are just as likely to get a headache after taking a placebo—and even more likely to have no reaction after taking MSG. When researchers examined the possible link between MSG and asthma, they got more or less the same results—leading the American College of Allergy, Asthma and Immunology to conclude that MSG is not an allergen.
Although the phenomenon of MSG sensitivity has been difficult to validate through scientific means, I know people who are convinced that MSG causes problems for them. You probably do too. They may go to extraordinary measures to avoid MSG; some even avoid foods that are high in naturally occurring glutamate such as Roquefort cheese. And if avoiding these foods improves your quality of life, I’m certainly not going to argue with you.
How to Spot MSG and Free Glutamate
Fortunately for those who want to avoid MSG, labeling laws require MSG to be listed in the ingredient list. It can’t be lumped under the more general term “spices and flavorings.” Furthermore, if food manufacturers use ingredients like hydrolyzed protein or autolyzed yeast, which contain free glutamate but not MSG, they are still not allowed to label the food “No MSG.”
However, manufacturers are allowed to use pure glutamic acid (the amino acid) in foods without listing it separately on the label; it can be identified simply as a “natural flavor.” Unfortunately, the only way to completely protect yourself against that possibility is to avoid all packaged and processed foods. Finally, if you want to minimize your intake even of natural sources of free glutamate, you’d also want to avoid parmesan and Roquefort cheese, soy sauce, nutritional yeast, peas, corn, tomatoes, tomato juice, and grape juice.
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