Thursday, April 30, 2015

Is MSG Safe?

Monosodium glutamate, commonly abbreviated MSG, is a very common chemical used to enhance flavors in food. MSG works by activating the "umami" receptors on the tongue, effectively enhancing flavors and making food taste a lot better. This is similar to the way sodium chloride (table salt) works, but MSG is much more powerful, so sodium content can be reduced by adding MSG to food. For this reason, many food companies use MSG as a food additive.

Despite these apparent advantages, most people would agree that MSG is unhealthy and should be avoided. Sensitive individuals even experience negative side effects after consuming food containing MSG. But what exactly is wrong with MSG? If a person is not MSG sensitive, is it okay for them to consume it in their food?

MSG 3D animated
Virtual model of monosodium glutamate
Before answering these questions, it would be best to start with the molecular structure of MSG. Monosodium glutamate, also known as sodium glutamate, is an ionic compound with the formula NaC5H8NO4. It is the sodium salt of glutamic acid, which occurs naturally in many foods. When it dissolves in water, it dissociates (splits apart) into two ions: sodium and glutamate.

The glutamate ion is responsible for the flavor-enhancing properties of MSG.

So what exactly is wrong with MSG? One common explanation is that the glutamate ion in MSG is a neurotransmitter which overexcites brain cells to the point of cell death. In one study, newborn mice that were treated with MSG developed brain lesions, not to mention other serious health problems such as stunted skeletal growth and female sterility.

This seems very serious. However, note that the mice treated were vulnerable newborns, and were injected with unnaturally high doses. Pretty much any chemical will cause problems when given in large enough doses. Furthermore, MSG is normally eaten, not injected.  Hence, the study does not apply to MSG in food.

What are the results when used in reasonable dosages? So far, human studies have been rather inconsistent, but the general results seem to show that MSG is harmless to the average person, and causes some slight issues in sensitive individuals. One double-blind, placebo-controlled study on reportedly sensitive individuals used 5-gram doses of MSG administered without food. The study found that the subjects tended to react more to the MSG than to the placebo, but that when the subjects were repeatedly tested, the responses to MSG were not consistent. When the researchers gave MSG with food, reaction rates were much lower.

Results of another study suggested that the apparent threshold dose is about 2.5 grams. Smaller doses did not result in symptoms.

Keep in mind, though, that food sensitivities are not uncommon – about 18 million Americans are sensitive to gluten, a component of wheat. Dairy is another product that many people cannot eat. A few sensitivities to MSG does not necessarily mean that MSG is harmful for everybody.

Still, many argue that MSG is unnatural, which makes it unsafe. To answer this, let's look at the manufacturing process.

Most MSG production uses bacterial fermentation, resulting in glutamic acid. Glutamic acid is a
naturally occurring amino acid present in many foods. It has the same flavor-enhancing properties as MSG, except that it's also weakly acidic. This means that glutamic acid contains a hydrogen atom which splits off when dissolved. This is undesirable. So the final step in the production process is to replace the hydrogen atom with a sodium atom. The result: monosodium glutamate.

The glutamate part of MSG is indistinguishable from the naturally-occuring glutamate in glutamic acid. They're essentially the same thing. And when you dissolve them, everything essentially splits apart, so there is no real difference between MSG and glutamic acid once you eat it. (In fact, MSG is partially converted back into glutamic acid when digested... but that's more than you need to know.)
Tomatoes on vine with white background
Tomatoes contain naturally-occurring glutamate.

Some, however, argue that glutamate exists in two forms, which are mirror images of each other. The "natural" form is L-glutamate, and the "artificial" form is a mirror image called D-glutamate. According to this argument, natural foods do not contain D-glutamate; manufactured MSG, on the other hand, contains both types of glutamate, and is therefore unsafe.

But this is not entirely true, according to a study published in Science. In the study, all tested glutamate-containing foods contain some of the "artificial" D-glutamate. And levels of D-glutamate in manufactured MSG are about the same as the levels in naturally-occuring glutamate. So "artificial" glutamate isn't really worse than the natural glutamate. Again, this makes sense because the glutamate in MSG is produced naturally.

Another argument is that naturally-occurring glutamate molecules are linked together as protein, whereas manufactured glutamate is not. Glutamate in protein cannot be utilized unless the human body breaks down the protein using enzymes, but glutamate in MSG is already broken down, so our body cannot control how much is used. This overload of free glutamate can kill brain cells.

This argument is, in fact, correct – partly correct, anyway. Foods such as meat, eggs, and peas definitely contain glutamate bound in proteins. However, other foods such as soy sauce, fish sauce, green tea, and Parmesan cheese contain high levels of free glutamate as well. Wikipedia has a useful table that shows some of the concentrations of free and bound glutamate in various foods. Foods containing MSG cannot be more dangerous than foods which naturally contain high levels of free glutamate.

Now this leaves one more question: is Parmesan safe?

This question is not as easily answered. I'll let you figure it out.

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