NutriStack
BCAAs and L-Tryptophan, timing-sensitive.
This is the classic large neutral amino acid transporter competition described in the central fatigue hypothesis. BCAAs are sometimes used deliberately to lower brain serotonin during exercise, which is the opposite of why people supplement L-tryptophan (to raise serotonin for sleep or mood). Taking a large BCAA dose at the same time as L-tryptophan reduces tryptophan's passage into the central nervous system and can therefore reduce its intended benefit. The interaction is dose- and timing-dependent rather than a safety hazard.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
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At a glance
- Substances
- BCAAs and L-Tryptophan
- Pair type
- Timing Sensitive
- Evidence (highest tier)
- Moderate
- Source citations
- 3 sources
- Stack Score effect
- −5 to your Stack Score (per scored timing-sensitive row).
- Scope
- Supplement × Supplement
- Last verified
- May 30, 2026
Timing Sensitive · Moderate evidence
Timing Sensitive
What is happening. This is the classic large neutral amino acid transporter competition described in the central fatigue hypothesis. BCAAs are sometimes used deliberately to lower brain serotonin during exercise, which is the opposite of why people supplement L-tryptophan (to raise serotonin for sleep or mood). Taking a large BCAA dose at the same time as L-tryptophan reduces tryptophan's passage into the central nervous system and can therefore reduce its intended benefit. The interaction is dose- and timing-dependent rather than a safety hazard.
Mechanism. BCAAs (leucine, isoleucine, valine) and L-tryptophan are both large neutral amino acids (LNAAs) that compete for the same carrier, the LAT1 transporter, at the blood-brain barrier. When plasma BCAA levels rise, the tryptophan-to-LNAA ratio falls, so less tryptophan reaches the brain. Because brain tryptophan availability is rate-limiting for serotonin synthesis, co-ingesting high-dose BCAAs alongside L-tryptophan can blunt the central serotonergic effect tryptophan is usually taken for (mood, sleep, calm).
Recommendation. Separate the two by at least 2 to 3 hours. Take L-tryptophan on its own, ideally on a relatively empty stomach or with a small carbohydrate source, away from any BCAA or high-protein dose. If L-tryptophan is for sleep, take it in the evening and keep BCAAs to around training earlier in the day. Avoid combining a large BCAA bolus (for example 5 to 10 g) with L-tryptophan in the same serving.
Minimum separation. 2 to 3 hours
Sources (3)
- Fernstrom JD. Branched-chain amino acids and brain function. J Nutr. 2005. PMID 15930466
- Blomstrand E. A role for branched-chain amino acids in reducing central fatigue. J Nutr. 2006. PMID 16424144
- Reviews of blood-brain barrier large neutral amino acid (LAT1) transport and competition among aromatic and branched-chain amino acids.
Stack Score
How this pair moves the number.
Effect on the composite score
If both BCAAs and L-Tryptophan are in the same stack, this pair applies −5 to your Stack Score (per scored timing-sensitive row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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