How science, research, and the latest tech shaped EFS

First Endurance is a research-driven company, and the thing about research is it’s always changing, and those changes are constantly revealing amazing, unrealized applications for endurance athletes. The science is always improving, so we’re always improving our product mix to give people access to the most-advanced endurance nutrition possible.

Reengineered in 2021, EFS is a prime example of this ethos, with new research into expected (fueling), unexpected (mental toughness), and unlooked for (flavor) technologies creating new opportunities to support athletes and improve performance.

In this blog post, Dr. Bucci explains the advances made with the latest EFS formula – and how the latest research made them possible.

Mind Games

We develop endurance nutrition for athletes aspiring to be the best that they can be in the most demanding situations. We’re not following the compressed, one-size-fits-all recommendations from major sports orgs that everybody else follows. Even the top exercise scientists aren’t certain those guidelines are good enough for elite athletes, and we’re in the business of being certain, so we designed EFS accordingly.

While revising the EFS formula, we noticed two trends of research dovetailing: research on what we’ll call “mental toughness” and research on an alpha amino acid called theanine.

For mental toughness, clinical research finds a correlation between improved performance and athletes who exhibit better inhibitory control – which is to say they’re less susceptible to the kind of pessimistic internal signaling we all experience while suffering during endurance exercise. These athletes are better able to block out internal stimuli (fatigue, burning muscles, pain, boredom) and focus on external stimuli (the race situation, positioning for the upcoming climb, maintaining target pace or power output), contributing to better results. It seems safe to assume all of that would be true, but we don’t assume anything.

This is where theanine connects to endurance athletics. All the evidence points to L-theanine rebalancing that tug-of-war between stimulatory panic mode and inhibitory control, maintaining calm, focus, and perspective when the demands of endurance training kick up your brain’s stressors.

In other words, L-theanine supports all of those qualities that predict better performance in clinical research studies, reinforcing your ability to push through pain rather than surrender to it. When you and everyone around you are already at your limit, that can be the difference between finishing first, finishing fourth, or – for ultra-endurance events – finishing at all.

The best way to win the mind games? Just don’t be vulnerable to them.

Not all Theanines are Created Equal

Theanine is an alpha amino acid that comes in two variations of chirality or “twists” at the molecular level: an L-form and a D-form. L-theanine works the way we want; D-theanine is basically a “blank” that produces a net negative effect by displacing its weight in the more effective L version, so we want to avoid it. That’s why we only use Suntheanine®.

Suntheanine® is a specific brand name of L-theanine produced by Taiyo Kagaku Co., Ltd., in Yokkaichi, Japan. The patented process of producing Suntheanine® uses the same enzyme that green tea leaves use to make L-theanine. The process avoids bothersome D-theanine forms, so 99.5% of the molecules in Suntheanine® are L-theanine. It also goes beyond just a compositional match to nature-identical conformation. Conformation is something that’s typically ignored about amino acids, but it’s extremely important for matching the successful human studies.

In fact, 99.5% purity and nature-identical conformation are why Suntheanine® is the most studied form of L-theanine. The research pointing to the beneficial effects of L-theanine is almost exclusively done with Suntheanine®, so it’s the only form of L-theanine we use – no cutting corners for price or larger market availability. We’re only interested in results, and clinical studies show that Suntheanine® is the best way to achieve them.

Performance or Flavor: Pick Both

It doesn’t matter how great a hydration mix is if you have to force yourself to drink it, or if – as an editor from a popular cycling publication once complained in private about one of our old flavors – it tastes like “swamp water.” You’re simply not going to drink as much or as often as you should.

As with the performance ingredients in EFS, recent breakthroughs in flavor technology gave us powerful new tools to tweak the formula’s flavor. There’s no longer a cloyingly, overwhelming saccharin taste or gradually accumulating sweetness fatigue over the course of multi-hour sessions and events, which can compound when a potent performance formula is mixed at a higher concentration. It’s elite hydration and fueling with a flavor profile that eliminates the usual tradeoff between performance or flavor.

Feedback from athletes who boost concentration to account for extreme efforts in extreme conditions is part of the reason we paid so much attention to the new sweetness profiles. EFS just tastes good, even when it’s mixed at higher concentrations in order to deliver more carbs and electrolytes on particularly hot, grueling days.

Even more amazing is that we were able to do it without any artificial flavors, which is something that wouldn’t have been possible without our focus on always taking advantage of new research and technologies to improve our products.

Balanced with your Body

Despite the importance of flavor, GI distress was the main issue to address while revamping EFS’s formula. We had to source the carbs right to keep the solution’s osmolality balanced at 7%, which is the sweet spot for GI and metabolic processing. By maintaining that balance, EFS avoids the risk of either bonking or suffering a mid-race gut punch from taking on too much of the wrong kind of fuel and throwing off your GI tract’s tolerance.

We’ve always pushed the low-osmolality angle for easier absorption and less GI distress, but EFS solves another issue: it dissolves better into water. The powder itself is noticeably more “feathery” than your typical hydration mix – light, like powdered sugar instead of granulated table sugar. It disappears into water more easily and is less prone to clumping and sludging up at the bottom of the bottle, which is an additional benefit for athletes who mix it at a higher concentration.


EFS includes branched-chain amino acids (BCAAs), which recent research shows help preserve late-stage energy production after you’ve been exercising at a high level for two hours or longer. For a deeper dive into this idea, refer to this BCAAs blog post, but I’ll include a summary here.

This is a relatively uncommon addition to hydration fueling mixes, because BCAAs only provide this benefit – emergency fuel production – under specific conditions. The exercise has to be strenuous and sustained; you have to be at your limit, burning through glucose intake and eating into glycogen stores, and you have to take the BCAAs during and throughout exercise. 

That last condition is the most important. It’s also the one that research on BCAAs tends to miss, and it’s the reason why no one else includes BCAAs in hydration or fueling supplements. Taking them before or after exercise won’t generate the same effect; if you want BCAAs to kickstart energy production when you’re deep into a training session or gearing up for a race finale, they must be taken while you’re actually exercising.

BCAAs are misunderstood as a source for fueling during exhaustive endurance exercise, but we include them in EFS because the research tells us to.

Addition by Subtraction

When it comes to the precise tolerances of high-intensity endurance nutrition, what you leave out can be (almost) as important as what you add. And we definitely left some things out. Vitamin C, protein – there are some notable absences in EFS that may surprise careful perusers of ingredients lists.

Vitamin C in particular is virtually universal across the hydration mix market. But not EFS. Why? Because clinical research told us it doesn’t belong and that it can actually be ergolytic (performance-decreasing) when ingested during exercise. If it’s included in a product meant to be used to support exercise performance, then it potentially causes more problems than it solves.

Vitamin C is, of course, important to immune support for endurance athletes, but it has to be done right, not just haphazardly thrown into any formula with no consideration of when that formula is being used by an athlete and for what purpose.

During exercise is not the right time to ingest vitamin C. Instead, it should be taken well before exercise to ensure it’s well assimilated, with any excess excreted. Doses of 500mg or more during exercise are excessive and problematic; lower doses during exercise are not problematic, but they’re also not helpful.

We do include vitamin C in MultiV, but since it can have a deleterious impact on endurance performance when taken during exercise, it doesn’t make sense to use it in EFS.

We had a choice of being like everyone else and adding vitamin C for familiarity – performance-decreasing effects and all – but we ultimately decided that EFS should be formulated for endurance performance.

Protein is another notable omission. We shelved it because it’s difficult to absorb, digest, and metabolize while you’re at or above threshold, so it falls under the same endurance-first exclusion policy as vitamin C.

Of course, it’s not as simple as that, and new research has been showing that under specific, controlled conditions, adding some protein to carb-electrolyte mixes has some benefits. While we are still exploring the use of proteins or protein hydrolysates (as in Ultragen, for post-exercise use), we have another answer to take during exercise.

Vegan and Gluten Free

We don’t necessarily make dietary restriction the focus of our formulations – recall the endurance-first policy – but we do of course want to ensure that dedicated athletes with dietary restrictions can take advantage of the research-driven advantages our products provide, regardless of whether their diets are a necessity or a lifestyle choice. Furthermore, our raw materials are all tested for food allergens, and those allergens are listed if present. If you don’t see it under Other Ingredients, then it’s not there.

EFS is suitable for vegan, vegetarian, and gluten free athletes dedicated to endurance exercise and training.


EFS is revolutionary because it uses research and new technology to support mental toughness and help athletes maintain calm, focused determination while powering more intense efforts in more extreme conditions than any other hydration mix – and it does so with a pleasant taste.

Nothing about this formula is a guess or a passive choice. Instead, every aspect – the carb source, the addition of Suntheanine® L-theanine, the exclusion of vitamin C, and the inclusion of glutamine and BCAAs as a working alternative to protein – was driven by clinical research and field testing at the highest level of competition.

April 04, 2023 — Luke Bucci
Tags: EFS research

Leave a comment

Please note: comments must be approved before they are published.

Did you find this post interesting and valuable or was it a waste of your time? Do you have a topic you’d like us to cover or a question you’d like answered? If so, leave a comment below and we'll get back to you right away.

    1 out of ...