Glutamine is the most abundant naturally occurring, non-essential amino acid in the human body. 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
Food sources of glutamine include:
Animal sources: meat, fish, eggs, milk, yogurt, ricotta cheese, cottage cheese,
Plant sources: beans, spinach, parsley, cabbage. Small amounts of free L-glutamine are found in vegetable juices and fermented foods, such as miso
Functions
A substrate for DNA synthesis.
Major role in protein synthesis.
Primary source of fuel for enterocytes (cells lining the inside of the small intestine).
Precursor for rapidly dividing immune cells, thus aiding in immune function.
Regulation of acid-base balance in the kidney.[citation needed]
Alternative source of fuel for the brain and helps to block cortisol-induced protein catabolism.
As a form of fixed nitogen by heterocysts, exchanged for photosynthate from undifferentiated cyanobacterial cells.
Polar (uncharged)
Glutamine is also marketed as a supplement used for muscle growth in weightlifting, bodybuilding, endurance and other sports.