It’s common knowledge that if you’re racing a marathon, half marathon or an ultra, you’re going to need to refuel during the race with gels, fluids, and other forms of carbohydrates.
In case you need a quick refresher, this is because glycogen is the primary energy source we use when running at marathon pace or faster.
Other possible sources of energy, like fats, are harder for the body to breakdown into usable energy. So, they are not very efficient and can’t supply energy quickly enough to sustain the body’s demands.
The problem with glycogen is that we can’t store enough to get us through the entire race.
Here’s so quick math to illustrate.
- We know from research that we can store between 1320 kcal to 2020 kcal of glycogen.
- Depending on your weight and fitness, running utilizes about 1kcal per kilogram of bodyweight per kilometer run.
Let’s say you weight 175 pounds (80kg) you would thus need about 3360 kcal (80kg x 42 km) to make it through the race
2020 kcal stored < 3360 kcal needed = 1340 calorie shortage.
Now, the simple solution to this would seemingly be to just continuously replenish your glycogen stores during the race with gels and fluids that contain carbohydrates.
But, if you’ve ever raced before, you know this isn’t quite as easy as it sounds.
Why You Can’t Just Take as Many Gels as You Want
The difficulty with using gels and other carbohydrates during a race is that there is a limit to how many calories you can process within a certain time-frame.
Your body can only digest and process around 350 calories per hour when running.
Even worse, this number dwindles the harder your run and the more tired you get. So, in the latter stages of a race this number might be only 250 calories per hour.
This happens because blood is needed to digest food in the stomach.
As you run faster and longer, the muscles you use for running require more and more blood to maintain pace. Therefore, your body shunts blood away from the stomach and to the working muscles.
Without blood, the stomach cannot digest efficiently.
That means even if you ingested 500 calories every hour, you might only be able to use 250 to 350 of the calories.
Unfortunately, that unused glycogen that you’re not able to process doesn’t just wait around until your stomach has more time to digest it.
Instead, the unabsorbed carbohydrates pull water into the intestines, causing a laxative effect, bloating, and discomfort.
This is one of the biggest mistakes runners make when trying to avoid bonking. They take too many gels or other carb sources and they aren’t absorbed or result in GI distress.
How to Get More Efficient at Absorbing Glycogen
Luckily, there are some things you can do to help you absorb and digest more glycogen:
Option 1: Train your stomach
This may seem obvious, but training your stomach to digest carbohydrates during exercise is one of the main reasons you need to practice your nutrition strategy during training.
In essence, you’re training your gut as well as you physical fitness.
Research shows that runners who systematically train their gut experience significantly fewer GI issues and can absorb up to 30% more carbohydrates during races.
Here’s how to practice and train your gut….
Week 1-2: Baseline Building .
Start with one “gut training day” per week during a long run or tempo session.
Begin with 30-45g of carbohydrates per hour using a 2:1 glucose-to-fructose ratio (more on this below). Practice consuming 150-200ml of fluid every 15-20 minutes.
Week 3-4: Volume Increase
Increase to 60g carbohydrates per hour while maintaining the same fluid intake pattern.
Studies show this level can be reached comfortably by most runners within 2-4 weeks of consistent practice.
Week 5-6: Race Simulation
Push to your race-day target (typically 60-90g/hour for marathon runners).
Research demonstrates that athletes who practice consuming large volumes during training show improved gastric emptying and reduced perception of fullness.
​Studies indicate that this progressive approach can reduce gastrointestinal symptoms by 26-47% and improve carbohydrate absorption by 45-54%.
Option 2: Optimize your carbohydrate type
The second option is to optimize the types of carbohydrates you’re using during the race.
Research has shown that different types of sugars are absorbed through a different transport mechanism. Meaning, they take different routes to get absorbed.
A good way to visualize this is thinking about traffic.
If you only have one road leading to the entrance to the park that can let in 50 cars per hour and then you split that road into two entrances, each of which can still let in 50 cars per hour, you drastically improve the speed at which you can get all the cars through.
This means if you combine different types of sugars, you can prevent some of the backlog that creates these GI issues.
The latest science supports that the most efficient combination appears to be fructose and glucose at anywhere from a .7 to 1.1 to 1 ratio of fructose to glucose.
If you have suffered from GI issues while taking gels or want to increase your overall glycogen intake, I highly recommend finding a gel or drink mix with this ratio.
My recommendation is Flow Formulas, which has a .8:1 ratio and is definitely the best tasting of all the drinks I have tried. But, there are a lot of products on the market now, so you experiment with what works best for you.
Option 3: Targeted Probiotics
More recent research has demonstrated that specific probiotic strains like Bifidobacterium and advanced formulations such as ProbioSEB Duo can significantly enhance carbohydrate absorption and metabolism during endurance exercise.
Enhanced Carbohydrate Processing
A landmark randomized controlled trial found that probiotic supplementation increased mean total carbohydrate oxidation from 1.87 grams per minute to 2.20 grams per minute during 2-hour cycling sessions [1].
This enhanced utilization occurs because probiotics increase both the abundance and activity of sodium-glucose transporter 1 (SGLT1), the key mechanism responsible for glucose absorption in the intestine.
Muscle Glycogen Sparing Effects
Bifidobacterium longum research shows particularly impressive results for endurance athletes.
Studies found that when combined with exercise training, this strain improved fatigue-associated markers including lactate, ammonia, and crucially, glycogen content compared to control groups [2].
The enhanced carbohydrate absorption allows the body to rely more heavily on ingested fuel rather than depleting precious muscle glycogen stores.
Gut Barrier Integrity and Nutrient Absorption
Finally, research shows that specific Bifidobacterium strains help keep your gut lining strong. [3].
This improved gut barrier integrity prevents the “leaky gut” syndrome that affects up to 70% of endurance athletes and reduces nutrient malabsorption.
Supplementing with these targeted probiotic strains can help you absorb and utilize more of their race-day fueling while experiencing fewer gastrointestinal symptoms.
This is why we created MAS Flush. It is the only probiotic specifically designed to address the exact needs and stomach issues endurance athletes face when training and racing hard.
The Bottom Line
Fueling is a critical component to your performance at every distance from the half marathon to the ultra.
Luckily, your digestive system responds to progressive training just like your cardiovascular and muscular systems.
And the research is pretty clear that athletes who systematically train their gut tolerance experience significantly fewer race-day GI issues and maintain higher carbohydrate absorption rates when racing.
So, start your gut training protocol immediately, regardless of where you are in your current training cycle.
Even four weeks of consistent practice can dramatically improve your digestive performance during endurance events.
