L-Glutamine, ranked by real cost

L-Glutamine is the most abundant amino acid in the body and serves as a primary fuel source for intestinal cells and immune cells. Under normal conditions the body produces enough on its own; it becomes conditionally essential under significant physical stress such as critical illness, major surgery, or severe burns. The evidence for supplementation is context-dependent. In critically ill and post-surgical patients, multiple meta-analyses show meaningful reductions in infection rates and hospital stay length — this is where L-glutamine has the strongest case. For gut permeability, a 2024 meta-analysis found significant improvements, but only at high doses (>30g/day) and short durations (<4 weeks). For healthy athletes and general "recovery" claims, the evidence is weak — a 47-study systematic review found no significant effects on muscle mass, aerobic capacity, or immune function in trained individuals. The gap between marketing and clinical evidence is wide here. Most consumer products sell 5g servings for "muscle recovery" — a claim the research doesn't strongly support at that dose. Products are useful for gut-permeability applications if dosed high enough, and meaningful in clinical recovery contexts. For general athletic use, honest answer is it's probably doing less than the label suggests.