This is the second installment in a series on the reimagined EFS and a mind-over-matter compound that makes perfect sense for maximizing your brain’s control of your exercise performance: Suntheanine® L-theanine. Theanine calms anxiety and stress (both physical and mental), helping you maintain perspective when an obstacle—a looming climb, a 90-degree turn into a headwind, another gap to close—threatens to crush your motivation. Theanine also supports immune health, especially during intense exercise when your body may become vulnerable as it depletes its reserves.

In this installment, Dr. Bucci explains the sources of theanine and why First Endurance insists on using only Suntheanine® L-theanine, derived from fermentative biosynthesis rather than theanine derived from tea or other synthetization processes.


Suntheanine was awarded the “Food Ingredient Research Award” at the 1998 Food Ingredients Europe and “Best New Product ” at Nutracon.

Suntheanine is protected by over 40 U.S. and international patents for its various physiological efficacies and L-isomer specific production processes.

Where is theanine found?

Except for one porcini-like mushroom (Xerocomus basius) and perhaps close relatives, theanine is found almost exclusively in green tea plants (Wan 2009). This is a bizarre scientific fact—almost nothing is that unique in nature. It’s also commercially available in bulk as a pure ingredient used in dietary supplements, where it’s made by one of two processes: chemical synthesis or fermentative biosynthesis.

Before going any further, note that theanine, being an alpha-amino acid, can come in one of two types: D-theanine and L-theanine. This is called chirality, and we’ll get into it more in the next blog installment. Suffice it to say for now that only L-theanine produces the calming effects we want, and only Suntheanine®—a brand of theanine produced via fermentative biosynthesis—meets our requirements for L-form purity and reliably consistent quality. Every other theanine source involves risks of contaminants, unwanted ingredients, or the counterproductive presence of high amounts of D-theanine, which effectively counteracts the positive effects of L-theanine.

Given those restraints, here’s our analysis of the three possible sources for theanine: green tea, chemical synthesis, and fermentative biosynthesis.

Theanine Sourced from Tea

Green, oolong, and black tea plants (Camellia sinensis) are the only practical dietary source of L-theanine. About 1-2% of tea’s dry weight is theanine, so a standard 200ml cup will have around 8-25mg theanine and heavy tea drinkers might consume 300mg of theanine daily (Sharma 2018, Wan 2009). The theanine in tea is also virtually all L-form (99.5%+), the chirality that produces calming effects.

Suntheanine is a patented pure form of L-theanine and is not an extract of green tea but rather is produced via a patented process that mimics the natural process in green tea leaves, resulting in a 100% pure L-isomer-theanine.

Given that tea provides so much L-theanine at such a high purity level, why use synthetically derived L-theanine? Why not just add green tea powder? Because we’re not making green tea smoothies; we’re making a high-level hydration mix.

Tea can certainly have its place in the saddle—think Hampsten, et al, sipping hot tea (and later tea with cognac) to keep going on the Gavia in ’88—but EFS and EFS-PRO are engineered for a specific goal: keeping you hydrated, fueled, and clear-headed enough to take advantage of that hydration and fuel. Adding green tea effectively adds all manner of other ingredients. That upsets the balance of ingredients and formulation we’ve dialed-in based on research and clinical studies, thereby compromising the mix’s overall effectiveness at doing what it’s designed to do.

Theanine sourced from Synthesis

One reason why theanine has not previously exploded on the health and wellness scene is that it is very costly and resource wasteful to extract from tea (especially compared to taking powdered tea extracts in pills or, you know, simply drinking tea). That means that a concerted effort, mostly in Asia, has been devoted to making large quantities of theanine at a reasonable cost by synthesis.

There are two options for synthesizing theanine: chemical synthesis and fermentative biosynthesis. The former is less expensive, but it involves unacceptable compromises in purity and control; the latter is pricier, but the purity and guaranteed control over the product make it the only source for premium endurance nutrition—at least, the only source that meets our standards.

“4.2. Chemical synthesis Major drawback of these methods is production of racemic mixture of D- and L-Th which are difficult to separate. Moreover, synthetic products are less preferred because of the use of chemicals with reported health hazards.”
(Sharma 2018 p.612)

Chemical synthesis

Like any chemical compound, theanine can be synthesized in a big vat by dumping the right chemicals into the right solution in the right order at the right temperatures. We immediately ruled out this route for three reasons: it doesn’t guarantee a high yield of L-theanine (as opposed to the undesirable D-form), it involves toxic compounds or solvents, and its product contains leftover reactants that need to be removed.

For example, a common chemical synthesis route uses phthalate compounds (which are endocrine disruptors at even tiny levels) and hydrazine (rocket fuel) along with other hazardous compounds to generate L-theanine (Wan 2009). If you don’t know where the theanine in a product comes from, this is a possibility.

Chemical synthesis also produces a 50:50 blend of D-theanine and L-theanine. If that feels random, well, it is; chance alone determines whether a chemically synthesized theanine molecule will twist left or right, and since D-theanine effectively cancels the benefits of a corresponding quantity of L-theanine, a 50:50 split may well produce a net zero effect. We refuse to leave anything to chance, so the final product is nowhere near our standards of chiral purity. Chemical synthesis can be modified to produce lesser amounts of D-forms, but that increases complexity and cost while still facing a steep climb to match the fermentative biosynthesis process we use, which always produces 99.5%+ L-theanine.

Fermentative biosynthesis

That leaves fermentative biosynthesis, which synthesizes theanine by using the same enzyme that green tea plants use to make theanine from simple, bioidentical L-form precursors. The process produces 99.5%+ L-theanine—about twice the amount of “good” theanine as chemical synthesis—using a stabilized and immobilized glutaminase enzyme system (Juneja 1999; Wan 2009). That means that, since it’s an L-amino acid, it was relatively simple to adapt tried and true production methods by switching to the right enzyme to make theanine instead of leucine or other amino acids that are in common production. This technology was developed to ensure purity for use in pharmaceutical intravenous feeding mixtures. It’s literal life-and-death stuff—no room for error.

We use only Suntheanine® L-theanine because the technology is that well worked out, that well controlled, and that well tested; we know exactly what it is, what’s in it, where it comes from, and how it’s made. This type of fermentation synthesis technology has been in large-scale use for decades, with Taiyo Kagaku Co., Ltd., in Yokkaichi, Japan using this process to commercially produce Suntheanine® since the 1980s. The science has been perfected, and the resulting guaranteed purity make Suntheanine® the most-studied theanine in peer-reviewed, published, human studies.

First Endurance’s literature review examined 60 human study publications (of ~571 since 1971) to understand theanine’s effects. Of those 60, at least 35 (58.3%) definitely did use Suntheanine®. Only 4/60 (6.7%) definitely did not use Suntheanine®, and one of those was green tea itself. We also concluded that, given the timing of publication and history of commercial L-theanine availability, many of the studies using an unknown theanine source (35%) were more than likely using Suntheanine®. All side effects in human studies of L-theanine were either the same as or less than those reported by placebo/control groups. Given L-theanine’s nature as a nutritional supplement, many of these studies included persons with pre-existing conditions, Rx drugs users, children and aged persons—populations who would be most susceptible to adverse effects and yet who experienced virtually none.

As noted above, Taiyo Kagaku has been producing and distributing Suntheanine® L-theanine since the 1980s, and Suntheanine® has undergone continuous rigorous regulatory testing during that time. Because of Japanese food and FOSHU (FOods for Special Health Use—or simply dietary supplements) regulations, an extensive amount of oversight has ensured the safety, purity, and reproducibility of Suntheanine® L-theanine. Those decades of scrutiny have resulted in no dietary exposure limits imposed by the Japanese Food Additive Association, which is an ongoing stamp of approval by regulatory agencies (Juneja 1999). In addition, the US FDA did not object to safety findings from an expert panel and affirmed Generally Recognized as Safe (GRAS) status (GRN000209) in 2007 (USFDA 2007) for Suntheanine®, but not for other sources. Other commercial sources of theanine have not been affirmed and may not have been subject to safety studies on their material for sale.

All of that may seem like a lot to take in. But we did our homework on this so you don’t have to. For purity and consistency, Suntheanine® L-theanine has been and continues to be the standard bearer.

We’d love to hear from you. Tell us what you think or ask us a question in the “comment” section. If you found this article beneficial, please share it with a friend.


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March 09, 2023 — Luke Bucci


ben said:

pursuant to my prior comment: question about dosage. a quick look at Amazon reveals that most manufacturers are creating this as a supplement in dosages >225mg, where EFS-Pro only has 50mg per serving. according to the pharmacokinetics, if one took a supplement, there would still be ~50% of that amount left in the bloodstream a few hours after ingestion. given those numbers, why wouldn't there be a higher dosage in the EFS-Pro product? is there a particular negative effect that would occur if one were to take a 225mg supplement around 1-2hrs before a long race?

ben said:

great article! just the right amount of scientific depth, and thanks for citing the papers so i can read them on my own!

i can't believe this is the first i'm hearing of L-Theanine in the endurance community….i'm always telling my athletes that the brain is the strongest muscle in the body. it's great to finally hear that it's being treated as such. thrilled to have a product that i know is giving me this mental edge. this could be why i like the product so much, even before i knew the significance of this ingredient.

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