Glutamic acid (glutamate) is an amino acid used by the body to build proteins. Under normal circumstances, humans are able to meet bodily glutamate requirements either from the diet or by making it from precursor molecules. Glutamate is the most common excitatory (stimulating) neurotransmitter in the central nervous system. Although glutamine and glutamic acid have similar names, they are structurally different.

The fluid produced by the prostate gland contains significant amounts of glutamic acid, and this amino acid may play a role in normal function of the prostate. In one study, symptoms of benign prostatic hyperplasia (BPH) were improved in a group of 45 men taking 780 mg of glutamic acid per day for two weeks and then 390 mg for the next two and a half months in combination with equal amounts of the amino acids, alanine and glycine, an effect also reported by other researchers.

Glutamic acid may have protective effects on the heart muscle in people with heart disease. Intravenous injections of glutamic acid (as monosodium glutamate) have been shown to increase exercise tolerance and heart function in people with stable angina pectoris.

The amino acid glutamic acid can be synthesized by humans, making it nonessential. Its presence in the diet, however, may facilitate optimal protein synthesis. The side chain of glutamic acid, like that of aspartic acid, contains a carboxyl group. Most of the glutamic acid in our bodies is incorporated into proteins, where its side chain often interacts with water or other polar group. At neutral pH (see acids), the carboxyl side chain can contribute negative charge to the surface of proteins, facilitating binding to positively charged areas on other proteins or membranes.

Glutamic acid is biosynthesized from a number of amino acids including ornithine and arginine. When aminated, glutamic acid forms the important amino acid glutamine. Because it has a carboxylic acid moiety on the side chain, glutamic acid is one of only two amino acids (the other being aspartic acid) that has a net negative charge at physiological pH. This negative charge makes glutamic acid a very polar molecule and it is usually found on the outside of proteins and enzymes where it is free to interact with the aqueous intracellular surroundings. On a molar basis, glutamic acid is incorporated into proteins at a rate of 6.2 percent compared to the other amino acids.

Most food sources of protein supply glutamic acid, so only a person deficient in protein would become deficient in glutamic acid.

Glutamic acid is generally free of side effects for the vast majority of people who take it; however, people with kidney or liver disease should not consume high intakes of amino acids without consulting a healthcare professional. Because over stimulation of glutamate receptors is thought to be a possible cause of certain neurological diseases (e.g., amyotrophic lateral sclerosis [Lou Gehrig’s disease] and epilepsy), people with a neurological disease should consult of physician before supplementing with glutamate.

Monosodium glutamate (MSG), the form of glutamic acid that is used as a flavor enhancer, has been reported in anecdotal studies to have a number of different adverse effects (including headache, fatigue, and depression). However, controlled trials have failed to confirm that MSG causes these side effects, and the safety of this compound remains controversial.

Sources of glutamic acid include high-protein foods, such as meat, poultry, fish, eggs, and dairy products. Some protein-rich plant foods also supply glutamic acid.