L-Glutamine (post-infectious IBS)

Tier 2 — promising · Gut barrier · IBS-D · Intestinal permeability

The primary fuel for intestinal epithelial cells and lymphocytes. A 2019 Gut trial (Zhou et al.) found 15 g/day for 8 weeks significantly reduced IBS-D symptoms and restored gut barrier function in patients with diarrhea-predominant post-infectious IBS. Effects in other IBS subtypes are not established. Healthy people with an intact mucosa already synthesise large amounts of glutamine in skeletal muscle, and additional supplementation adds little — the indication is narrow and condition-specific.

Dose: 15 g/day in 3 divided doses for post-infectious IBS-D; minimal benefit in general healthy population