L-Glutamine: Fuel for the Gut and More
is one of the most popular supplement ingredients to support gastrointestinal health and intestinal-barrier function. But this versatile amino acid also offers an array of additional benefits for overall health. Here’s a look at the many benefits of l-glutamine, including its impact on immune health, wound healing, exercise performance, and stress.
WHAT IS L-GLUTAMINE?
L-glutamine is the most abundant amino acid in the human body. It’s the primary metabolic fuel for many rapidly proliferating cells in the body—including the epithelial cells of the small intestines (enterocytes), lymphocytes, macrophages, fibroblasts, and other immune cells.
L-glutamine can be converted into other amino acids or . It’s a precursor for nucleotides and DNA synthesis and one of three amino acids required for the production of glutathione. The most concentrated stores of l-glutamine are in skeletal muscle. It can be synthesized from glutamate by the enzyme glutamine synthase or metabolized for energy by the enzyme glutaminase.
Although l-glutamine is not considered an essential amino acid, the demand for this foundational nutrient can increase during endurance exercise, trauma, surgery, or other forms of stress.
L-GLUTAMINE AND INTESTINAL HEALTH
Within the , l-glutamine is of greatest importance to the enterocytes and for the maintenance of the small intestinal mucosa. Colonocytes also use l-glutamine as an energy source, but they depend more on short-chain fatty acids (SCFAs).
The rapidly dividing enterocytes are so metabolically active that they consume more l-glutamine than any other organ cell. Enterocytes express high activity of glutaminase and low activity of glutamine synthase. They attain a steady supply of l-glutamine from the luminal contents of the small intestines and the systemic blood supply.
Studies have shown that oral supplementation with l-glutamine can also be an effective way to support the healthy structure and function of the intestinal mucosa.
L-GLUTAMINE AND IMMUNE HEALTH
L-glutamine may support immune health through at least three mechanisms:
Supporting intestinal-barrier function. L-glutamine indirectly supports aresponse by fueling enterocytes and the health of the intestinal mucosa. Non-beneficial bacteria and toxins are less likely to translocate and trigger an immune response in the gut-associated lymphoid tissue (GALT) when intestinal-barrier function is healthy.
Fueling immune cells. Lymphocytes, neutrophils, and macrophages all depend on l-glutamine as a primary source of fuel. L-glutamine supports the healthy proliferation and activity of these immune cells.
Supporting the production of glutathione. L-glutamine is one of three amino acids needed to produce glutathione. As an essential antioxidant within immune cells, glutathione is critical for supporting healthy immune function.
Numerous studies have shown l-glutamine administered to patients via IV or added to total parenteral nutrition (TPN) supports a healthy immune response. There is also evidence that oral administration of l-glutamine supports immune function as well.
L-GLUTAMINE AND TISSUE HEALING
L-glutamine serves as an energy source for fibroblasts, which are central to the process of wound healing. Fibroblasts lay down the extracellular matrix and create the collagen structure to support new cells. L-glutamine supports the rebuilding of injured tissue by serving as a substrate for nucleotides, which supports healthy cellular replication.
The body’s response to injury—whether it’s from surgery or other trauma— involves the shunting of l-glutamine out of the blood and into the injured tissues for repair. Studies show that l-glutamine may support wound healing and helps maintain healthy levels of l-glutamine after trauma or injury.
L-GLUTAMINE AND STRESS
The demand for l-glutamine increases when the body is . The release of cortisol accelerates protein breakdown from muscles, releasing l-glutamine into the blood. Simultaneously, cortisol increases glutaminase activity in enterocytes.
When stress is intense or prolonged, l-glutamine stores can become depleted. Consequently, less l-glutamine is available as an energy source for the intestinal lining and the immune cells. Therefore, to support healthy immunity and intestinal-barrier function, it’s reasonable to consider l-glutamine during periods of stress.
L-GLUTAMINE AND SPORTS NUTRITION
As mentioned earlier, the skeletal muscle is the body’s main storage depot for l-glutamine. So it’s not surprising that studies show that prolonged exercise and heavy training are associated with lower blood levels of l-glutamine.
L-glutamine is often included as an ingredient in sports nutrition products because it’s thought to support muscle mass and immune function during exercise. However, a 2019 systematic review concluded that l-glutamine supported weight management but did not significantly affect body composition or athletic performance.
A dipeptide form of l-glutamine (l-alanyl-l-glutamine, or Sustamine) has shown some promise in sports nutrition. Sustamine has demonstrated a better ability to support hydration than l-glutamine alone. Small studies suggest it also supports exercise performance in athletes.
L-GLUTAMINE SUPPLEMENT INGREDIENT FORMS
L-glutamine is available as an oral supplement in two forms: free-form l-glutamine and the dipeptide Sustamine. The free-from version is the most widely available.
Most studies suggest that both forms of l-glutamine have similar abilities to support intestinal and . Both types are found in formulas to support the intestinal mucosa and barrier function.
Sustamine may offer some advantages over free-form l-glutamine because it’s more stable when combined with other nutrients and dissolves more readily when mixed with liquids of any temperature.
L-GLUTAMINE SUGGESTED USE
is generally considered to be a safe supplement ingredient, but concerns have been raised about theoretical effects of supplementation on neurological and cellular health. As always, clinicians should consider each patient’s individual situation when evaluating the risks and benefits of l-glutamine or any other nutritional supplement.
The observed safety limit (meaning the amount deemed safe to take daily over time) of l-glutamine is 14 grams per day. However, many human studies have utilized higher amounts without reporting any safety concerns.
Studies of oral supplementation of l-glutamine in humans have evaluated daily amounts ranging from 1 gram (in the context of rehydration and sports) to 44 grams (in the context of intestinal and). A daily amount of 10 grams was shown to support healthy immune function in athletes.
Researchers often administer l-glutamine in amounts that are dependent on body weight. In a 2012 study, daily oral l-glutamine supplementation of 500 mg/kg (about 34 grams for a 150-pound person) was found to support the health of intestinal mucosa and barrier function.
L-glutamine is a fundamental nutrient for the maintenance of gastrointestinal health. But it’s also worth considering supplementation with l-glutamine or its dipeptide Sustamine to support intestinal mucosal function, intestinal-barrier function, , wound healing, and exercise performance.