Glutamine is the most abundant amino acid in the body. It is synthesized from glutamate by an enzyme called glutamine synthetase when ammonia from other amino acids and alpha-ketoglutarate, an intermediate of metabolic Krebs cycle, are combined together. Glutamine serves as a metabolic fuel for the cells of your immune system (neutrophils, thymocytes, lymphocytes, macrophages), cells in the intestinal tract (for energy metabolism), brain (for neurotransmitter production), liver (in urea and glucose synthesis), kidneys (for renal ammoniagenesis), hair follicles (ensuring you don’t go bald), and, most importantly, for your skeletal muscle cells (in protein synthesis).
Glutamine rules the construction process of those items plus a multitude of protein-dependent reactions in all of the cells and tissues in the body. Your muscles and plasma are loaded with glutamine which captures more than 60% of the entire intramuscular pool of amino acids. Adipose tissue (body fat), lungs, liver and the brain also synthesize glutamine, but the extent and importance is not even close to that of the muscles. Your gut uses glutamine as one of the major fuel sources which is extremely substantial during dieting. In fact, your intestines will eat up to 40% of all glutamine used in the body, regardless of whether you decide to quit eating “cold turkey” in the relentless attempt to get that shredded look to show off your muscle definition or let yourself gorge on everything in sight with a knowingly worthless justification of being in a “bulking” cycle.
If you want your body to make sense of all metabolic reactions, thus turning the food you eat into usable energy, it must have a hard-working and efficient method. If you are in a mass gaining phase of your training, then you need to bulk up by eating an enormous amount of food and the mucosal cells of your intestines have to recognize these as nutrients and get them to appropriate places in the body via blood while protecting you from any possible bacteria. The more you eat, the greater the turnover of the intestinal mucosa, and the more construction and protection material is needed for the re-structuring of your gut, which should come from amino acids (mainly glutamine).
Theoretically, the formula seems simple. Desired additional muscles equals more intense workouts which equals more fuel for training and energy and tissue restoration which then equals more food which equals increased digestion and metabolism which equals more work for the GI tract which equals more fuel for the gut from glutamine. It’s a long process!
Your muscles synthesize and store enormous amounts of glutamine, so when you weight train in the gym and breakdown lean tissue cells, you use the glutamine stored in the muscles much faster. In the end, your muscles need additional glutamine just to survive. And that’s not all!
Besides the muscle-food connection, glutamine supports the immune function and body’s replenishing abilities, especially during times of stress. Working out, not getting enough sleep and strict dieting all spark a fire of stress inducing catabolism which suppresses your immunity. Glutamine links your anabolic environment, your immune function and your muscle cells. In other words, your body’s ability to restore and rejuvenate itself is dependent upon the efficacy of the immune system. At its optimal state, your immune system creates the desired fertile muscle building foundation to restructure muscle cells that you have broken down in the gym. But the efficacy of your immune system is directly influenced by the plasma concentration of glutamine which depends on the rate of muscle synthesis and release of glutamine.