THE EVOLUTION OF HIGH-CARB FUELING

How EFS and EFS-PRO supercharge carbs 

By Dr. Luke Bucci, PhD

INTRODUCTION

EFS and EFS-PRO were way ahead of the times when first launched in the naughts. But today is the Roaring Twenties, and a lot of research water has flowed under the ultra-endurance fueling bridge, taking it away to longer and faster performances. Updated EFS and EFS-PRO modifications are based on the latest technology and research on how carbs and sugars are absorbed from inside the gut and into the bloodstream.

EFS and EFS-PRO were redesigned with four advantages:

1) long-time knowledge of endurance athlete needs during races;
2) long-time experience in delivering more water, more electrolytes, and more fuel (carbs);
3) digging deeper into emerging science and research on how gut cells really work, going beyond the obvious and hackneyed; and
4) field testing with real athletes under real racing conditions until it’s right.

In this blog post, First Endurance Chief Scientific Officer Dr. Luke Bucci explores the final part of item #2 (more carbs) by unpacking #3. Dr. Bucci explains how the latest research into specific carb receptors in the gut, GLUT2 and GLUT4, maximize the absorption of carbs in the form of glucose, without the need to gamble with the potential negatives and conversion process required with traditional carbs.

CARBS ARE STILL KING

First, a reminder that carbs are everything for fueling.

Fueling has gone through paroxysms of upheaval, including fat loading and fat-breakdown metabolites (keto-acids) instead of carbs, which turned out to be impractical, expensive and even damaging. Carbs are still King for fueling long-term exercise, and our bodies know it. It’s just easier in an aqueous system (our bodies) to store and move around hugely soluble glucose instead of fats, which need a lot of cellular machinery to be made soluble, be handled, and be broken down into muscular energy. Fats/ketos simply never will be able to ramp-up as fast as carbs.

If carbs are King (they are), then glucose is the crown jewel. That’s the fuel your cells turn into ATP, which in turn powers every muscle movement you make. The updated EFS and EFS-PRO formulas provide more glucose faster than before, which is how both formulas can deliver more carbs without GI distress – for EFS-PRO, hitting hourly intakes of 60, 90, 120, or more grams of carbs.

FINDING – AND EXCEEDING – CARB LIMITS

Carb intake, transportation, storage, and conversion into ATP has limits. Research found those limits quickly, but mostly under laboratory settings, which don’t reflect the conditions of true maximal, long-term endurance performance. This is not a dig at research, it’s just the amalgam of putting exercising people into settings less realistic than actual competitions, being careful not to stress them as much as they would be in real racing, and being more focused on finding new things than trying to get 100% of what really happens. Research from many fields has since moved beyond those self-imposed limitations, initiating a series of revelations about carb absorption that have revolutionized fueling.

The first of those revelations was about GLUT5 and fructose. More up-to-date research has since pushed the fueling narrative beyond GLUT5, but a quick glance  confirms that the industry is still largely stuck in the past. There’s more to GLUTs than GLUT5 (GLUT = GLUcose Transporter). EFS and EFS-PRO have moved beyond simply maximizing fructose delivery, and into expanding the hiding-in-plain-sight GLUT receptor family members to maximize BOTH fructose and glucose uptake into your bloodstream when you need it most – during exercise. Here’s why.

GLUT5 + FREE FRUCTOSE IS OUTDATED

Research into the changes GLUT5 receptors undergo in the gut during fueling and exercise showed that loading your gut with enough fructose increases overall carb delivery by effectively circumnavigating your body’s normal glucose uptake limits. Consuming high quantities of fructose prompts your body to create additional GLUT5 receptors, which pull fructose from your gut into your gut cells so it can be converted into glucose to feed muscles.

This was a simple solution for maximizing a backdoor, upregulated facet of carb intake, and it pushed fructose into the carb fueling limelight, causing mass hysteria to literally shove more and more fructose down our throats.

But here’s what was forgotten in the fructose frenzy: GLUT5 is only one part of a larger GLUT whole for getting carbs into the bloodstream. Also overlooked were other more important issues: Guts have more ways to get glucose into cells than fructose, and glucose doesn’t have the negative effects of free fructose. Too much fructose leads to oxidative stress, inflammation, and – eventually – long-term health issues.

Finding a way to supercharge carb delivery without relying on free fructose would be a win-win. Fortunately, science marches on.

BETTER RESEARCH, BETTER CHO SOLUTIONS

The big change for EFS to reach higher carb intakes with improved performance and GI-tolerance was simple, but not obvious, because it’s related to something seldom discussed: the mechanics of how carbs are digested.

For example, how glucose loads “talk” to your gut from signals in your mouth, stomach, inside the many feet of gut, and your miles of bloodstream that ultimately get signals from each and every one of your cells is only recently known to be complex, interactive, extremely adaptive and fast-changing. Your body’s relationship to carbs is much more dynamic than isolated knowledge of a few data points for glucose and a few hormone signals (like insulin or nowadays, GLP-1). It’s a continuous, ever-changing system.

That area of research has been traditionally underfunded and underappreciated because increasing carb uptake is not as lucrative as decreasing carb uptake for pharmaceutical drug research and profits; however, new discoveries are happening all the time lately, due to better attention, better assays, and more funding.

The biggest beneficiaries of this new, more effective research are GLUT 2 and GLUT4, which are receptors that operate on glucose only, skipping the fructose middleman and giving your body more of what it really wants for fuel.

GLUT2 IS THE TWO-FACED RECEPTOR

Keep in mind that all this absorption/uptake talk is about getting carbs from your belly into the cells lining your gut. All the glucose (and other monosaccharides like excess fructose) that gets into gut cells also needs to get out to the bloodstream and liver. GLUT2 does that by staying on the bottom side of gut cells to send glucose on its way to the rest of the body.

GLUT2 is stored up inside gut cells. When gut cells take in more glucose, GLUT2 is sent to the bottom of gut cells to offload the supply. At least, that’s what we always thought. That’s still correct, but it’s a limited understanding of how GLUT2 works – and how it can be optimized for maximum fueling.

The new finding about GLUT2 is that it also goes to the top of gut cells to bring glucose in, working alongside trusty GLUT1, SLGT1, and GLUT4 receptors for extra glucose absorption, not just expulsion. Nobody bothered to look at GLUT2 doing a 180 until recently, but doing so has identified yet another avenue for getting more glucose into gut cells, allowing higher and higher glucose intakes to be useful for fueling endurance exercise.

GLUT4 IS THE NEW GLUT5

Recent research has shown that GLUT4 works as a surge handler for glucose absorption, similar to how GLUT5 works for fructose. Like GLUT2, GLUT4 is stored up inside gut cells, just waiting to activate to bring in a glut of glucose by quickly zooming to the top of gut cells when a large amount of glucose is inside the gut, backing up the large-but-stable amount of GLUT1 (SLC2A1) and sodium-dependent SLGT1 receptors that take up the most glucose all the time. (For more on GLUT1 and SLCGT1, check out the EFS/EFS-PRO Research Packet.)

GLUT4 translocation can be trained to store more ready-for-action glucose intake by what is being called gut training – increasing carb uptakes during exercise to acclimate your GLUT army for higher carb loads. Getting your gut to make more GLUT4 available takes a few weeks and trial-and-error, but this is a big reason why hitherto nauseating intakes of glucose and carbs are now commonplace.

MAXIMUM GLUCOSE + MAXIMUM FRUCTOSE

The blend of carbs in EFS and EFS-PRO delivers maximal glucose with better tolerability through multiple avenues of CHO absorption. It also does so while eliminating the issues that high fructose loads can cause.

That’s not to say fructose doesn’t have its place. In fact, research has also shown us a better way to use fructose: by consuming it with a glucose as part of the disaccharide sucrose, which is just table sugar – glucose:fructose. Here’s how the new EFS strikes the ideal balance between pure glucose and the Glc:Fru hybrid, sucrose.

EFS has always had a predominant amount of maltodextrin, which is a short-chain glucose string that has better stomach emptying, gut tolerability, and glucose delivery than glucose itself. This is why you see a lot of fuel products with maltodextrin and free fructose.

Updated EFS dropped some maltodextrin to be replaced by more sucrose, maintaining a high, belly-friendly glucose load while also upping the fructose intake safely without free fructose excess. Because sucrose empties the stomach similarly to glucose – and because more glucose administered with fructose increases fructose uptake and conversion to glucose in gut cells – EFS is perfectly balanced to maximize fructose uptake at a Glc:Fru ratio higher than standard 1:1 or 2:1.

Updated EFS-PRO simply switched from maltodextrin to CCD (Cyclic Cluster Dextrins) as the major glucose source, with sucrose again for that sweet spot Glc:Fru ratio. EFS-PRO takes advantage of stomach emptying, tolerability and glucose delivery to gut cells provided by CCD – beyond what glucose/maltodextrin combos can do.

THE SWEETEST SCIENCE

This is a bonus item, related to #4 on the list in the introduction, but it’s something that can’t be ignored with carb-delivery mixes.

Being able to ingest as much fuel as needed throughout long endurance events is just as important as the science behind how to maximize that fuel. Long-term exercise causes flavor fatigue, especially with sweetness, which becomes cloying and reduces intake of fuel and liquids. Even the best designed fuel is worthless if an athlete loses the desire to ingest it properly. That means flavor matters, and it can’t just be an agreeable flavor tested in the sterile vacuum of a taste-testing room, so EFS prototypes were tested for palatability, sweetness, and tolerability under real race conditions to get the balance right for extreme conditions. We wanted to make EFS continue to taste best.

The carb changes we made also improved flavor, preventing a too-intense sweet taste common with high-fructose products. Fructose is 1.5x sweeter than sucrose, sucrose is less sweet, glucose has little sweetness, and maltodextrin/CCD have no sweetness. Eliminating fructose means that EFS and EFS-PRO are both far lighter on the palate than a fructose-laden mix, reducing flavor fatigue and removing one additional barrier to multi-hour fueling.

The flavors were further developed with new flavoring systems, and the increased sucrose meant that other sweeteners (stevia, monk fruit, fake stuff) were unnecessary and removed – there are no artificial sweeteners or flavoring agents in either formula.

SUMMARY

It’s not easy to study how glucose gets into the gut and into the bloodstream because it happens in so many ways and is ever-changing – especially during high-stress activities like endurance exercise. Research that only measures glucose uptake in non-athletes doesn’t represent glucose absorption in the real world of endurance athletes. Until recently, experimental foibles in measurement missed the reality of lightning-fast changes in gut cells to absorb more glucose.

Newer research into guts and carbs showed that high intake of free fructose activates GLUT5 receptors, which pull in more fructose to convert to glucose, skipping your gut’s glucose limits and increasing overall fueling. That prompted a shift to fructose-heavy fueling formulas, which can cause long-term issues and require the additional step of post-absorption conversion to fructose.

The latest research provides an even better solution, showing that increased glucose intake activates GLUT4 and GLUT2 receptors like GLUT5 receptors in gut cells, but they pull in more glucose instead of free fructose, eliminating the need for excess free fructose while still boosting carb uptakes. The latest EFS and EFS-PRO formulas are built to take advantage of these new findings, providing more glucose, more tolerability, and better overall performance.

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