New Epiphanies Max Out Carb Intakes for Endurance Athletes

By Dr. Luke R. Bucci and Jeff Feliciano


One of the most frequent questions we get is: How many carbs do I need to take during my long-duration events, races or training lasting more than three hours? The prevailing wisdom has long been set at 30-60 grams per hour (120-240 calories/hour), and usage directions for EFS & EFS-PRO are based on this time-tested range. But emerging research suggests athletes can ingest more and more carbs per hour: 90-140 grams or 360-560 Calories. That’s 1.5 to 19 times MORE carbs than the endurance experts have agreed upon for years!

So why are the amounts of carbs you are supposed to consume during long-duration exercise apparently going up to levels that might make an experienced athlete’s stomach hurt just thinking about it? The trick is to understand the science (well, you can leave that to us), know the necessary factors for high carb intakes, train your gut to handle higher carb intake, and individualize your carb intake per hour according to your body weight and hydration needs.

If you want to skip straight to the answer, then jump down to our Individualization guide to customize your own approach to carbs; however, for those who want the why behind the what and the how, read on for a little background about how scientific understanding of carbs and endurance athletes has recently evolved.

[Note: We will use CHO and/or Carbs/carbs as abbreviations for Carbohydrates throughout this Blog]

What Are Other Ultraendurance Athletes Really Doing?

Many studies have measured how many grams of carbs endurance athletes actually take in during long races/events, and that typically averages out to 45-54gCHO/h. Most athletes try to take in more than that, but GI symptoms prevent reaching the higher carb intakes (over 60gCHO/h). Thus, the need for Gut Training to be able to handle more carb intake during ultraendurance activities is crucial for breaking past the 60g/h barrier successfully.

Factors for Success of High Carb Intakes

First, it’s important to note that there are certain requirements that must be met for the higher carb loads we’re discussing here to actually be effective:

  1. Exercise Duration: 3 hours and longer
  2. Exercise Intensity: as fast as you can maintain with reserve for a sprint to the finish
  3. Total Carb Intake per hour: 90 grams or more (up to 150 g/h)
  4. Gut Training: the key to making high carb intakes work for you – this takes time
  5. Individualization: Go with your lean body mass (one size does not fit all)
  6. Sufficient hydration and electrolytes
  7. Be prepared for GI side effects

Many of these requirements are built into serious endurance athletics. Duration of 3+ hours? Check. Intensity? Check. And of course staying hydrated and expecting the occasional GI distress are standard considerations. Items 3, 4, and 5, though – those are what we are focused on here.


The Recent Epiphanies Reshaping Carb Intake

Carbs used to be so simple – just take in plenty of sugar or glucose or maltodextrin or a combination thereof. This is what EFS, EFS-PRO, and Liquid Shot were created to deliver, and they do it well (more on this later). But slamming more and more carbs into your body has limits, even with ultra-endurance distances and despite the recent research opening the floodgate. Before getting into the nuts-and-bolts of how to carb up, let’s get down with some history about carbs and exercise.

Glucose Legacy

Twentieth-century exercise physiologists focused on glucose (dextrose) for carb delivery because that’s what’s in your blood, that’s what’s stored as glycogen in muscle and liver, and that’s the primary fuel “burned” by muscles. Given that basic fact, exercise physiologists were looking for various ways to squeeze more glucose into you for decades, but limits were quickly found as endurance events became longer and longer. The limit was getting glucose past the gut and into your bloodstream without causing GI distress from unabsorbed carbs, but those early researchers had a limited understanding of how your gut really works to absorb and metabolize sugars.

Fortunately for athletes, science marches on, and game-changing gut adaptation epiphanies have recently been pinned down, making an impact on fueling for endurance events. Here are some of the bigger epiphanies.

Epiphany #1: MTCs Were a Carb Revolution – All About GLUT5 (recently renamed SLC2A5)

MTCs means Multiple Transportable Carbohydrates, which really gathered steam in the mid-2000s and are now the norm. In its simplest form, MTC formulas add large amounts of pure fructose to other carbs, usually glucose or glucose polymers (maltodextrins), in ratios of 2:1 or 1:1. These high fructose ratios were studied early in order to maximize the newly understood effect of sneaking fructose into the gut with a forgotten transport receptor on your absorptive gut lining cells (enterocytes). These receptors are called GLUT5 (we’ll stay with the more familiar GLUT5 name for this blog). GLUT5 prefers to pull pure fructose out of the inside of your gut and throw it into your enterocytes. Since there are two major glucose transporters (SLGT1 & GLUT2), adding GLUT5 to the mix is where the MTCs name derived.

Adding enough fructose to glucose sources increases overall carb delivery by effectively circumnavigating your body’s glucose uptake limits – letting fructose in the back door of intestinal lining cells while the front door is blocked by the glucose queue. Once it’s absorbed, fructose is then converted into more glucose, up to the amount of your gut’s ability to convert it.

MTC carb studies on endurance exercise showed that carb grams per hour can be increased to previously untenable amounts, especially for exercise lasting three hours or more. A consensus of research shows that sustained carb intakes of 90g/h as Glc:Fru combinations (usually 2:1 or 1:1) usually leads to improvements in endurance performance, which in turn led to a plethora of Glc:Fru products for endurance athletes that we have today. However, other ratios of Glc:Fru products for endurance athletes have not received attention recently at higher intakes. Of course, First Endurance was ahead of the game as usual, and capitalized on MTCs in the mid-2000s when EFS, and later, EFS-PRO were introduced. Our field testing backed up the laboratory research that MTCs can improve long-duration performance.

Epiphany #2: Instant Adaptation Opens Glucose Floodgates

Very recently, another research epiphany overturned intestinal dogma by showing that GLUT2 (recently renamed SLC2A2), another transporter for glucose, can rapidly show up on the apical, or inward absorptive side of gut enterocytes – within minutes after ingestion of high glucose loads. This on-the-fly adaptation lets your body get more glucose from the gut into the gut lining and, thus, into the bloodstream than before.

Normally, GLUT2 is how gut enterocyte cells dump glucose absorbed from the gut out the other side (basal side) into circulation; however, GLUT2 was not seen on the absorptive (apical) side of gut enterocytes because researchers did not see it during rest or normal meals. It was thought that the SGLT1 transporter (recently renamed SLC5A1) was sufficient to internalize normal glucose intakes. But researchers never looked for GLUT2 in extreme conditions, like during endurance exercise or high carb intakes. This finding is so new that gastroenterology textbooks still show GLUT2 receptors only on the basal side of gut enterocytes, but this will change with time.

Here’s the new news: When your gut gets a lot of glucose quickly, your gut nervous system sends cellular commands to make more GLUT2 glucose receptors on the absorptive apical side, and this happens quickly! In minutes! It was evident that your enterocytes normally keep a supply of GLUT2 receptors hanging out inside themselves, just waiting to be directed to top (apical) or bottom (basal) sites depending on how much glucose you just ate. As soon as the inside-gut levels of glucose drop to more manageable levels, the added apical SLC2A2 receptors disappear just as quickly. GLUT2 is still pushing absorbed glucose out of enterocytes into circulation on the basal side, as always.

This normal phenomenon has only recently been elucidated, but it explains 90g/h or higher carb intakes being manageable. But of course it’s not that simple. Can you simply glug down more carb drinks per hour and perform longer and stronger? Not so fast – ramping up to 2-3 times more carbs than usual at once will still lead to GI disasters. There is another, much more important and quantitative way to increase your gut carb uptake during endurance exercise: Gut Training.

Epiphany #3: Gut Training for Increased Carb Intake

Studies have shown that training your gut to accept higher carb intakes during exercise can be accomplished in two weeks. One two-week study (Costa 2017) had athletes ingesting 30g of carbs every 20 minutes for two hours running at 60% VO2max, five days per week, while maintaining their normal training loads. That shakes out to 90gCHO/h or 180gCHO during each two-hour session. The subjects (29, but only10 women and 15 men completed the study) ingested carbs as a 2:1 Glu:Fru combination in solid (“disc” aka chewable tablet) form with 400 ml flavored liquid. It’s important to note that the subjects’ body weights were 67-76kg (~150lb).

Subjects also ran under placebo (flavored water) conditions and again with the same amount of carbs as a food (AmazeBalls from Australia) with 4g protein and 4g fat per feeding. Running performance and blood glucose levels were improved by the Glu:Fru discs but not by the food balls, compared to placebo conditions.

In this study, 29 men and women had four dropouts (DNFs) from adverse GI complaints (14%). For the 25 finishers, although GI complaints were reduced when retested after the study was completed, there were still some GI complaints, but close to normal levels seen with lower carb intakes (<60gCHO/h), indicating that the gut receptors were trained to handle larger carb loads. Compared to the first carb trial, both carb sources (discs and food balls) had reduced GI complaints at the end of two weeks.

This study presented a model for training the gut to more easily handle larger carb loads for ultraendurance athletes. Individual biology is also obviously important, so the hourly amount isn’t universal and should be adjusted individually according to your body weight to prevent GI distress.

Individualization for Increased Carb Intake

Don’t simply follow the study protocol listed above, as it only applies to a specific demographic: well-trained athletes weighing ~150lb. If you are under 140lb or more than 160lb, those gCHO/hour don’t match the research and may push you into forbidden territory for results – and for GI side effects.

So how do you tailor this approach to yourself, to determine what you actually need to consume to reach the magic grams/hour numbers? And how do you keep this process simple and make its application relevant to your preferred fuel source? You individualize!

We’re providing the handy table below so you can see how to individualize your carb intake using EFS & EFS-PRO powder amounts to match the gCHO per hour for 150lb (70kg) persons used in the Costa study for gut training for 90 gCHO/h over 2 hours. We are also showing the original recommendation for 60 gCHO/h and increased amounts for 120g CHO/h for heavy-duty CHO intake.

To keep this simple, we calculated how many scoops of EFS or EFS-PRO each bodyweight needs, and how much water (in fl oz like most water bottles) is needed to be added to the scoopfuls to reach a 10% CHO concentration. The goal is to drink at least that many fl oz every hour, preferably in 3 equal installments every 20 minutes. Keep in mind that you may need more fluid per hour than the fl oz in the Table – simply add water based on your traditional needs. It’s OK to drink more dilute concentrations if that works out better logistically. For body weights under 154lb, you may need to ingest additional fluids, preferably water, each hour.

Table 1: How to Use EFS or EFS-PRO for Gut Training by Your Body Weight

Body weight (pounds) 60 gCHO/hour 90 gCHO/hour 120 gCHO/hour
Scoops EFS Scoops EFSPRO Fill with fl oz H2O Scoops EFS Scoops EFSPRO Fill with fl oz H2O Scoops EFS Scoops EFSPRO Fill with fl oz H2O
80 3 10 2 5 15 20
100 4 13.5 6 20 3 8 25
125 2 5 17 3 25 4 10 34
154 6 20 9 30 12 41
175 3 26 4 11 37 14½ 49
200 3+ 8 27 12 40 6 16 54

Note 1: grams CHO have been rounded up to the nearest whole number.

 If you encounter GI distress that’s too much to handle, try using an amount in between the gCHO/hour that you know you can handle and the amount that was too much. For example, if you cannot tolerate 90 gCHO/h, try 75 gCHO/h by using the halfway amounts between 60 and 90 gCHO/h.

If gut training and training exercise simulating a real event go well, you should be ready. Gut training this way you can max out your performance by maximizing your fuel intake, staying hydrated, and not losing electrolytes during long duration events. We also calculated the electrolyte intakes and even at the highest CHO intake (120 gCHO/h), they are not excessive and within actual usage and controlled study intakes.

The other important piece to this puzzle is when to start ingesting higher amounts of carbs. Current advice is to start early, with a dose 30 minutes before starting exercise, then start ingesting your drinks at 20 minutes after the start for 3 servings per hour, as in Gut Training. Others argue to use your usual practices until 2 or 3 hours into an event, and then ramp up your carb intake. This issue is why you need to try increasing carb intake, even after Gut Training, before you participate in an actual event. You know what you can take better than we do, especially when pushing your limits.


Using gCHO/kg/h is a good starting point to individualize how much carbs you can take during exercise because endurance athletes aren’t all uniformly lean. Getting close to a carb dose per hour that should be ideal for you lets you fine-tune your training to determine what really works for you, faster, sooner, and with less bonking or belly sloshing and GI distress.

Gut Training is the “new” message for achieving and maintaining higher-than-usual carb intakes during endurance exercise longer than three hours to improve performance without running into GI tolerance problems. Benefits of reaching 90g carbs or more per hour after gut training are improved performance and less GI distress, but not zero GI discomfort or symptoms. The unique EFS-PRO formula has solved these issues based on extensive feedback over years of successful usage.



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August 25, 2022 — Luke Bucci
Tags: research

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