Occurrences in nature
Glutamine is the most abundant naturally occurring, non‑essential
amino acid in the human body and one of the few amino acids
that directly cross the blood‑brain barrier. In the body, it is
found circulating in the blood as well as stored in the skeletal
muscles. It becomes conditionally essential (requiring intake
from food or supplements) in states of illness or injury.
Dietary sources of L‑glutamine include beef, chicken, fish, eggs,
milk, dairy products, wheat, cabbage, beets, beans, spinach, and
parsley. Small amounts of free L‑glutamine are also found
in vegetable juices and foods, such as tofu.[unreliable
Aiding gastrointestinal function
In recent studies, glutamine‑enriched diets have been linked with
intestinal effects including maintenance of gut barrier function and
cell differentiation. This may relate to the fact that the intestinal
extraction rate of glutamine is higher than that for other amino
acids, and is therefore thought to be the most viable option when
attempting to alleviate conditions relating to the gastrointestinal
tract. These conditions were discovered within the gut between
glutamine‑enriched and non‑glutamine‑enriched diets. However,
even though glutamine is thought to have "cleansing" properties
and effects, it is unknown to what extent glutamine has clinical
benefits, due to the varied concentrations of glutamine in varieties
of food. Glutamine may help to protect the lining of the
gastrointestinal tract or mucosa. It has been suggested that people
who have inflammatory bowel disease IBD (ulcerative colitis and
Crohn' s disease) may not have enough glutamine. However, two
clinical trials found that taking glutamine supplements did not
improve symptoms of Crohn' s disease. More research is needed.
Examples for the usage of glutamine
In catabolic states of injury and illness, glutamine becomes
conditionally‑essential (requiring intake from food or supplements).
Glutamine has been studied extensively over the past 10–15
years and has been shown to be useful in treatment of serious
illnesses, injury, trauma, burns, and treatment‑related side‑effects
of cancer as well as in wound healing for postoperative patients.
Glutamine is also marketed as a supplement used for muscle
growth in weightlifting, bodybuilding, endurance, and other sports.
Evidence indicates that glutamine when orally loaded may increase
plasma HGH levels by stimulating the anterior pituitary
gland. In biological research, L‑glutamine is commonly added
 to the media in cell culture.