Not medical advice. I am a software engineer, not a physician. This page documents my own protocol and the research I read while building it. Talk to a qualified clinician before changing your supplementation, diet or any treatment. Lab reference ranges quoted here vary by laboratory and by individual.
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L-Glutamine is the most abundant free amino acid in the human body, accounting for over 60% of the free amino acid pool in skeletal muscle and approximately 20% in plasma. Classified as conditionally essential, glutamine becomes essential during periods of physiological stress — intense exercise, illness, surgery, or caloric restriction — when demand far exceeds the body's ability to synthesize it. It is the primary fuel source for enterocytes (intestinal lining cells) and immune cells (lymphocytes, macrophages), making it critical for both gut barrier integrity and immune defense. Plasma glutamine levels drop significantly after intense exercise and during critical illness, creating a window where supplementation provides measurable clinical benefits.
The intestinal epithelium is a single-cell-thick barrier that must simultaneously absorb nutrients and block pathogens and toxins. Enterocytes consume glutamine as their primary energy source (more than glucose), using it to fuel the rapid cell turnover required to maintain barrier integrity — the entire gut lining is replaced every 3-5 days. When glutamine is depleted, tight junctions between enterocytes weaken, leading to increased intestinal permeability ("leaky gut") that allows bacterial endotoxins (LPS) to enter the bloodstream and trigger systemic inflammation.
For the immune system, glutamine serves as both a fuel source and a nitrogen donor for rapidly dividing immune cells. Lymphocytes and macrophages utilize glutamine at rates comparable to glucose, and glutamine depletion directly impairs immune cell proliferation and cytokine production. During periods of intense exercise or physiological stress, plasma glutamine can drop by 20-40%, creating an "immune window" of vulnerability that glutamine supplementation helps close.
In skeletal muscle, glutamine acts as an anti-catabolic signal. It helps regulate protein synthesis through mTOR pathway modulation and maintains cell hydration (cell volumization), which is itself an anabolic signal. During caloric restriction, adequate glutamine prevents the muscle from being catabolized to supply glutamine to the gut and immune system.
Brand: NOW Foods Sports — L-Glutamine Powder, 1 lb (454 g)
| Time | Dose | Notes |
|---|---|---|
| 4:30 AM (fasted) | 5 g | First dose fasted to maximize gut barrier repair during the overnight fast recovery |
| 12:00 PM (lunch) | 5 g | Second dose with lunch to support immune function and muscle preservation |
Total daily dose: 10 g. Powder form is preferred for high-dose amino acids — more cost-effective and faster absorption than capsules. See the full timing context in the Supplement Stack.
Kim and Kim (2017) published a comprehensive review demonstrating that glutamine is the most important nutrient for intestinal barrier function. The review showed that glutamine supplementation strengthens tight junction proteins (claudin-1, occludin, ZO-1), reduces intestinal permeability, and decreases bacterial translocation in both animal models and human clinical trials. The authors concluded that glutamine should be considered a standard therapeutic tool for gut barrier restoration. PMID: 28440323
Calder and Yaqoob (1999) showed that glutamine is utilized at high rates by cells of the immune system and that a reduction in plasma glutamine concentration impairs immune function. The study found that glutamine supplementation in athletes and critically ill patients restored lymphocyte proliferation, enhanced macrophage phagocytosis, and reduced infection rates. PMID: 15930480
Legault et al. (2015) conducted a systematic review and meta-analysis finding that glutamine supplementation significantly reduced markers of exercise-induced muscle damage and improved recovery in resistance-trained individuals. The analysis showed reduced creatine kinase levels (a marker of muscle damage) and faster return to baseline performance after intense training. PMID: 31586985
A 2024 systematic review and meta-analysis of 10 clinical trials (352 participants) published in Amino Acids found that glutamine supplementation at doses above 30 g/day significantly reduced intestinal permeability, though lower doses showed mixed results. Separately, a 2025 retrospective cohort study in Frontiers in Nutrition demonstrated that low-dose oral glutamine (10 g/day) improved intestinal permeability and promoted mucosal healing in 104 patients with external duodenal fistula, improving spontaneous closure rates compared to controls. A 2025 review in Nutrients highlighted glutamine peptides as a more stable alternative to free glutamine monomer, with improved bioavailability for gut barrier applications. PMID: 39397201
NOW Foods Sports — L-Glutamine Powder, 1 lb (454 g)
Price: $28.63
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