L-Glutamine vs L-Theanine

Mechanism

L-Glutamine is the most abundant amino acid in plasma and skeletal muscle. It is the primary fuel source for enterocytes (intestinal epithelial cells) and rapidly dividing immune cells (lymphocytes, neutrophils). Glutamine maintains intestinal tight junction integrity by modulating tight junction proteins (occludin, claudin-1, ZO-1), preventing intestinal hyperpermeability ('leaky gut'). It serves as a nitrogen shuttle between tissues, is a precursor for nucleotide synthesis (purines and pyrimidines), contributes to gluconeogenesis, and buffers ammonia via glutamine synthetase. During catabolic stress (illness, surgery, intense exercise), glutamine becomes conditionally essential.

Standard Dosing

5-10g daily

Timing

On empty stomach for gut healing. Post-workout for muscle recovery. Dissolves easily in water.

Cycle Duration

8-12 weeks for gut healing; ongoing for maintenance

Side Effects

• Generally well-tolerated
• Bloating at high doses
• Constipation
• Headache
• Theoretical excess glutamate conversion in sensitive individuals (excitotoxicity concern)

Contraindications

• Hepatic encephalopathy (glutamine to glutamate to ammonia conversion)
• Reye's syndrome
• Severe renal failure
• Some cancers are glutamine-dependent (discuss with oncologist)

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Mechanism

L-Theanine (gamma-glutamylethylamide) crosses the blood-brain barrier via the large neutral amino acid transporter. It increases alpha brain wave activity (8-13 Hz, associated with relaxed alertness), enhances GABA, serotonin, and dopamine levels in the brain, and antagonizes glutamate excitotoxicity by blocking glutamate binding at AMPA, kainate, and NMDA receptors. It also increases BDNF and NGF expression, supporting neuroplasticity. The combination of glutamate antagonism and GABA/serotonin enhancement produces anxiolysis without sedation — a 'calm focus' state.

Standard Dosing

100-200mg daily (or as needed for acute anxiety/focus)

Timing

Flexible: morning for calm focus (stack with caffeine), before stressful events, or evening for relaxation/sleep onset. Onset: 30-60 minutes oral, 15-20 min sublingual.

Cycle Duration

ongoing or as needed

Side Effects

• Headache (rare)
• GI discomfort (rare)
• Dizziness at very high doses
• Generally extremely well-tolerated

Contraindications

• Very few — one of the safest supplements available. Caution in severe hypotension.

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