Both monosodium glutamate and sodium nitrite are used to flavor and season foods -- and to preserve them as well. Both can be dangerous for you if you eat them in high enough quantities, however. That said, the U.S. Food and Drug Administration considers each to be safe for consumption.
Sodium Nitrite Basics
Sodium nitrite gives cured meats their pink color, as it preserves the hue after cooking, as well as acts as an anti-toxin for botulism. Nitrites are present naturally in many vegetables, but preserved meats, such as hot dogs and sausages, contain the highest quantities per serving. Because nitrites are a food additive and because of their potential for toxicity, the FDA regulates how much sodium nitrite is allowed in foods, limiting it to no more than 500 parts per million for finished foods, including smoked and cured fish, as well as meat and meat products.
Unlike sodium nitrite, MSG is used primarily as a flavoring agent rather than a preservative. MSG is frequently used in canned foods, processed meats and Chinese food. While there is no limit to the amount of MSG allowed in foods, the FDA requires it to be listed as an ingredient in prepared foods. MSG occurs naturally in foods, where it is called glutamate, but in the early 1900s, it was isolated as a chemical compound by a Japanese scientist. The chemical makeup of MSG and glutamate is the same, and the majority of glutamate in your diet is from protein foods, and only a small amount, around 0.55 gram, is from added MSG.
How Much to Eat and Side Effects
When consumed in excessive quantities, 22 to 23 milligrams per kilogram of body weight, sodium nitrite is fatal. Sodium nitrite, when it mixes with your stomach acid during digestion, creates nitrosamines. In turn, while there are no limits to how much MSG can be safely consumed, some people claim that they are sensitive to MSG, even in small quantities. This condition is commonly known as Chinese restaurant syndrome because MSG is so frequently used in Chinese fast food, although symptoms may result from eating any foods high in MSG, not just Chinese fast food. Symptoms include flushing, numbness, headaches, increased sweating and a swelling feeling in your face. While most people recover without any treatment, severe reactions, including chest pain, irregular heartbeats, trouble breathing and swelling in the throat, require emergency medical care.
Other Potential Dangers
According to Oregon State University, nitrosamines are carcinogenic. A 2006 issue of “World Journal of Gastroenterology” included a review of studies over 20 years and concluded that there is a clear association between increased risk of gastric and esophageal cancer and consumption of nitrite and nitrosamines. While there are no indications that MSG is carcinogenic, a 2010 issue of “Cephalagia” included a human study which found that consuming high quantities of MSG led to increased incidences of headaches and head muscle tenderness, as well as raised blood pressure levels.