L-Tryptophan for Performance Enhancement
Often used for sleep, can tryptophan improved training outcomes?
I’ve been extremely interested in optimizing amino acid intake for athletes, especially peri-workout. Each week we’re investigating an amino acid to determine how it influences hypertrophy, fat loss, and performance.
In the last 2 weeks, we’ve explored L-Leucine and the Branched Chain Amino Acids, which are indispensable for hypertrophy and fat loss.
This week, in the spirit of Thanksgiving, we dig in to research on an essential amino acid often supplemented for improving sleep and associated with the drowsiness after eating turkey: L-Tryptophan.
In this article, we will explore the potential of L-Tryptophan for hypertrophy, fat loss, and performance enhancement.
To be honest I was surprised by the nuance and lack of clarity and consensus regarding the role and significance of L-tryptophan and its metabolites for body composition and performance, so bare with me!
L-Tryptophan & Exercise Performance
Given the association of L-Tryptophan with drowsiness and the fact this amino acid is commonly used as a supplement to improve sleep, I was skeptical about the role it would play as a pre- or post-workout supplement to improve performance and training outcomes.
Indeed, tryptophan does seem to improve sleep at >1g. (5)
But what about performance and training outcomes?
Now of course, all of the essential amino acids are required for the synthesis of muscle. But would L-Tryptophan pre-workout make you drowsy by increasing serotonin and 5-HT in the brain?
When trials look specifically at exercise performance, conflicting results are found and the efficacy of tryptophan supplementation is not yet definitive as far as I can tell.
For example, research dating as far back as 1988 has found L-tryptophan supplementation to improve exercise performance, with total exercise time increased by 49.4% and a lower rate of perceived exertion with L-tryptophan supplementation compared to a placebo, for which the authors credit a potential increase in pain tolerance. (3) However, consequent research from 1992 replicating this study in trained athletes has disputed these unusually impressive results and found no improvements between groups. (4)
But it didn’t stop in 1992. A more recent double-blind placebo-controlled cross-over trial from 2010 found L-tryptophan supplementation increased peak power output, average anaerobic power output, and power output in healthy young men. (2)
These papers debate over the question of whether increasing 5-HT levels in the brain as a result of L-tryptophan supplementation induce fatigue by increasing drowsiness or increase performance by increasing pain tolerance.
The 2010 paper argues for the latter, and also mentions the kynurenine pathway as worthy of consideration - and the kynurenine pathway does indeed appear to be a crucial consideration.
It turns out there are two major biochemical pathways for L-Tryptophan: one is the serotonin pathway, from which melatonin is derived.
However, there is a second major pathway called the kynurenine pathway, and the metabolites from this pathway play fundamental biological roles for many of the best-known benefits from exercise: improved energy, decreased inflammation, and neuroprotection. (1)
For example, the kynurenine pathway can lead to formation of NAD+, a fundamental substrate for energy production.
Under high cortisol and inflammatory conditions, kynurenine is produced to control inflammatory responses.
An adaptation to exercise is an intramuscular increase in an enzyme that converts kynurenine to kynurenic acid. Research has demonstrated that kynurenic acid production increases as an adaptation to exercise as evidenced by a significant increase of kynurenic acid in sweat after 28 days of an exercise regiment, concurrently with a decrease of kynurenine. (6)
Paraphrasing from this paper (6):
Elevated kynurenic acid may have important biological consequences and does not penetrate the blood brain barrier, but has been shown to reduce inflammation and modulate motility of the colon, increase renal excretion, reduce heart rate, and exert cardioprotective effects.
Again, the data is not definitive yet regarding the role and clinical significance or kynurenine or its metabolites, but in vitro data has found kynurenic acid induces protein synthesis and increases muscle size, and in mice it prevents muscle loss during periods of activity. (6)
Summary
While data is not definitive regarding the role of L-tryptophan in training outcomes or exercise performance, it is an essential amino acid necessary for health, function, and building muscle. At the very least, it seems reasonable consume an essential substrate for muscle growth and sleep quality.
While there is controversy over data that has found a performance enhancement effect, no data I’m aware of has demonstrated a negative effect on performance from L-tryptophan supplementation. Research has either found benefits or no difference - so there appears to be no risk and only upside.
Furthermore, since exercise has been shown to increase the enzyme that converts kynurenine (from tryptophan) into kynurenic acid, and kynurenic acid is implicated to have notable anti-inflammatory, neuroprotective, cardioprotective effects in addition to brain functioning, anti-ulcerative activity, and digestion regulation, I would personally at the very least ensure adequate intake of this amino acid.
In conclusion, I personally include L-tryptophan peri-workout, and I certainly will experiment with various dosages and timings on exercise performance and perceived exertion/pain tolerance.
This was a bit more detailed of an article because the research on L-tryptophan with regard to body composition and performance is quite nuanced.
Despite that, I hope it was helpful, and welcome any questions you have.
In any case, enjoy plenty of turkey!
Yours in strength,
Daniel J. Furtado, CPT, LMT, Owner of Honor Strength
www.honorstrength.com
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References
L-Tryptophan Supplementation Can Decrease Fatigue Perception During an Aerobic Exercise with Supramaximal Intercalated Anaerobic Bouts in Young Healthy Men
Effect of L-tryptophan supplementation on exercise performance
L-tryptophan supplementation does not improve running performance