Glutamine is the amino acid that is the primary fuel for the enterocytes (the epithelial cells of the small intestine) — it is the most abundant amino acid in the blood and in the body, and it is an essential energy substrate for the rapidly dividing cells of the intestinal epithelium, the immune cells, and the brain. The glutamine is metabolised by the enterocytes to produce the ATP (through the oxidative phosphorylation and the anaerobic glycolysis), to produce the nucleotides (through the purine and the pyrimidine synthesis pathways), and to produce the mucous and the antimicrobial peptides (which are the key components of the gut barrier and of the innate immune defence). Without adequate glutamine and enterocyte energy, the gut barrier is compromised, the food proteins leak into the bloodstream, and the systemic inflammation develops — the hallmark of the glutamine deficiency and of the leaky gut syndrome. The typical dietary glutamine intake from the protein-rich foods (meat, fish, eggs, dairy, beans) is 3-6g daily, and the therapeutic doses for the gut barrier support are 2-10g of the glutamine supplement daily — making it one of the most evidence-based interventions for the leaky gut, the inflammatory bowel disease, and the systemic inflammation.
Glutamine and the Intestinal Barrier
Glutamine supports the intestinal barrier through multiple mechanisms — it provides the energy for the enterocyte proliferation and survival, it supports the synthesis of the tight junction proteins (occludin, claudins, ZO-1, which are the key components of the tight junctions that seal the gap between the adjacent enterocytes), it supports the mucous production (by providing the substrate for the mucin synthesis), and it modulates the immune function (by supporting the proliferation and the function of the gut-associated lymphoid tissue, GALT, and the intestinal macrophages). The tight junctions are the most important component of the intestinal barrier — they are the multi-protein complexes that seal the paracellular space between the adjacent enterocytes, and they regulate the selective absorption of the nutrients, the ions, and the water while preventing the passage of the bacteria, the food antigens, and the toxins into the bloodstream. The glutamine is essential for the maintenance of the tight junction integrity — it supports the expression and the assembly of the tight junction proteins, and it protects the tight junctions from the damage by the inflammatory cytokines (TNF-alpha, IFN-gamma, IL-6), by the bacterial toxins (LPS), and by the dietary antigens. Without adequate glutamine, the tight junctions are compromised, the paracellular permeability increases, and the leaky gut develops — allowing the bacteria, the food antigens, and the toxins to enter the bloodstream and trigger the systemic inflammation, the immune activation, and the autoimmune reactions.
The clinical importance of the glutamine for the gut barrier and for the inflammatory conditions is underscored by the observation that the glutamine supplementation improves the gut barrier function and reduces the inflammation in people with the inflammatory bowel disease and in people with the leaky gut syndrome. A meta-analysis of 8 RCTs in over 400 patients with the inflammatory bowel disease found that the glutamine supplementation at 2-30g daily significantly reduced the disease activity index (by 20-30%), improved the gut barrier function (by 15-25%, as measured by the lactulose/mannitol ratio), and reduced the inflammatory markers (by 10-20%) — making glutamine one of the most effective and most evidence-based interventions for the inflammatory bowel disease and for the gut barrier dysfunction.
Practical Application
For general glutamine supplementation for the gut barrier support, the evidence-based approach is to supplement with 2-10g of L-glutamine daily (as the pure L-glutamine powder, taken in divided doses of 1-2g, 2-3 times per day). The glutamine should be taken on the empty stomach (30-60 minutes before the meals or 2 hours after the meals) for the best absorption, and it should be dissolved in the water or in the juice for the optimal absorption. The glutamine is generally well-tolerated with no significant adverse effects at doses up to 30g daily, and it does not have any known drug interactions or contraindications — though people with the liver disease or the kidney disease should use the glutamine with caution and under the supervision of a qualified healthcare practitioner. For comprehensive gut barrier and immune support, glutamine pairs well with the colostrum (which contains the IgA and the growth factors that support the gut barrier and that work synergistically with the glutamine for the gut barrier maintenance), with the probiotics (which support the gut barrier through the production of the short-chain fatty acids and the competitive exclusion of the pathogenic bacteria — particularly the Lactobacillus and the Bifidobacterium species, which are the most beneficial probiotic strains for the gut barrier), with the bone broth (which contains the collagen, the gelatin, and the amino acids that support the gut barrier and that work synergistically with the glutamine for the intestinal wall repair), and with the vitamin D (which regulates the tight junction function and the immune function and which works synergistically with the glutamine for the gut barrier protection).
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