Gln is the standard three-letter abbreviation for glutamine, one of the 20 amino acids that make up proteins in the human body. It is the most abundant amino acid in the bloodstream, making up roughly one-fifth of all circulating amino acids. Your body can produce glutamine on its own, but during serious illness or intense physical stress, demand can outpace supply, which is why scientists classify it as “conditionally essential.”
What Glutamine Actually Does in the Body
Glutamine’s defining chemical feature is a nitrogen-containing group on its side chain. That nitrogen is the key to one of glutamine’s most important jobs: shuttling ammonia safely through the bloodstream. Skeletal muscle produces most of the body’s glutamine, then releases it into the blood so other tissues can use it as fuel or as a raw material for building new molecules.
In the liver, glutamine feeds directly into the urea cycle, the process that converts toxic ammonia into urea so you can excrete it. This makes glutamine a central player in nitrogen balance, helping the body dispose of waste from protein metabolism without letting ammonia accumulate to dangerous levels.
Fuel for the Gut Lining
The cells lining your small intestine (enterocytes) burn through glutamine at a high rate. It is their primary energy source, powering their rapid division and turnover. Beyond simple fuel, glutamine supports the production of tight junction proteins, the molecular seals between intestinal cells that prevent bacteria and undigested food particles from leaking through the gut wall into the bloodstream.
When glutamine is scarce, the consequences for the gut are measurable. Animal and clinical studies show that glutamine deprivation leads to shrinkage of the tiny finger-like projections (villi) that absorb nutrients, along with ulcerations and cell death in the small intestine. The expression of key barrier proteins drops, and those proteins get redistributed away from the junctions where they’re needed. In practical terms, this means a weakened intestinal barrier.
Immune Cell Energy Source
White blood cells are among the hungriest consumers of glutamine in the body. Lymphocytes, macrophages, and neutrophils all rely on it to multiply, produce signaling molecules called cytokines, and carry out their bacteria-killing functions. Immune cells partially oxidize glutamine through a process called glutaminolysis, converting it into energy and building blocks for DNA and RNA. This is especially important because immune cells divide rapidly during an infection or after an injury.
Glutamine also influences which genes immune cells switch on. It activates signaling pathways that promote cell proliferation and enables T cells and B cells to produce antibodies. When glutamine levels fall, macrophages produce fewer inflammatory signals, and lymphocyte proliferation slows. This is one reason critically ill patients, whose glutamine stores are depleted, often face a higher risk of secondary infections.
A Building Block for Brain Signaling
In the brain, glutamine plays an essential but indirect role in communication between neurons. Brain support cells called astrocytes synthesize glutamine and shuttle it to nearby neurons, where it serves as the primary raw material for making two neurotransmitters: glutamate (the brain’s main excitatory signal) and GABA (the main inhibitory signal). Without a steady supply of glutamine from astrocytes, neurons become depleted of both neurotransmitters, disrupting the balance of excitation and inhibition that underlies normal brain function.
Glutamine itself is not neuroactive, which is precisely why it can travel safely between cells without triggering unwanted signaling. It only becomes a neurotransmitter after neurons convert it internally.
What Happens During Critical Illness
Under normal conditions, skeletal muscle produces enough glutamine to meet the body’s needs. During severe trauma, sepsis, or prolonged stays in intensive care, that equation breaks down. Demand from immune cells, the gut, and healing tissues spikes while muscle mass, the main production site, shrinks rapidly. Plasma glutamine concentration drops, and that drop is itself a prognostic marker: lower levels in sepsis patients correlate with worse outcomes.
Because glutamine is a precursor for DNA and RNA building blocks, the cells that suffer most from a shortage are those dividing fastest, particularly immune cells and gut lining cells. Clinical evidence supports intravenous glutamine supplementation for critically ill patients receiving nutrition through an IV, and it is considered standard care in that setting. Most patients normalize their plasma levels with 20 to 25 grams per day, and no adverse effects have been attributed to supplementation at these doses.
Glutamine, Exercise, and Muscle Recovery
Exhaustive exercise causes a temporary drop in circulating glutamine, which may partly explain the immune suppression athletes sometimes experience after intense training. Supplementation has been shown to support glycogen replenishment after exercise and reduce markers of muscle damage in both animal and human studies. Daily supplementation can lessen the skeletal muscle damage caused by exhaustive exercise, though the timing of intake matters for effectiveness.
For healthy adults, acute doses up to 20 to 30 grams appear safe and well tolerated. Studies using up to 0.65 grams per kilogram of body weight (about 45 grams for a 150-pound person) reported no abnormal ammonia levels or adverse effects.
Food Sources of Glutamine
Glutamine content in food ranges enormously, from trace amounts in apple juice to nearly 9.5 grams per 100 grams in wheat germ. Among common whole foods, the richest sources per 100 grams are:
- Beef: approximately 1,230 mg
- Tofu: approximately 600 mg
- Eggs: approximately 560 mg
- Corn: approximately 400 mg
- White rice: approximately 300 mg
- Skim milk: approximately 275 mg
Glutamine can contribute anywhere from 1% to 33% of a food’s total protein content, depending on the source. Whole grain bread sits at the high end of that ratio, while kidney beans sit at the low end. A varied diet that includes animal protein, soy, eggs, and grains generally provides enough glutamine for healthy individuals without supplementation.