What it is:
We all have individualized gut microbiomes, hydration, micro- and macronutrient needs. Therefore, we are the best person to judge what works for our bodies and consciously observe what works during training. If you decide to participate in an endurance event, you must experiment to find what works for you and/or work alongside your Nutrition Advisor to get a personalized protocol.
This piece will focus on running a marathon but can be utilized for any endurance sports that require vast amounts of energy reserves over long periods of time. We delve into the foundations of hydration, carbohydrates, and the current research on the best way to prepare and fuel your event.
Purported claims:
Items to consider for endurance nutrition:
Fuel timing, quality, and quantity
Fructose to glucose ratio for fueling
Hydration and electrolyte balance
Gut health
What the science says:
Endurance training is not just about running or cycling long distances—optimal performance requires practicing your strategic fueling, hydration, and recovery. Personalizing your nutrition, practicing with different food and drink strategies, and building a strong gut microbiome may prevent GI issues and Bonking, allowing you to perform at your best on race day. Determining what is best for you can be overwhelming, so we’ve dived in deep into the fueling world below. However, working with your Apeiron Life nutrition advisor can help fine-tune these elements to meet your specific needs.
Avoiding Runner’s Trots, Cramps, and GI Issues
The exact reason for diarrhea and cramping during an endurance sport is not fully understood, as digestion is a highly complex process, on top of which we put our bodies through major inflammatory stressors when we perform endurance races.
There are many factors to explore when experiencing gastrointestinal issues during your training. Look at your hydration, electrolytes, fructose:glucose ratio, carbohydrate amounts, inflammatory response, and overall health status.
What do we know so far?
Our system first breaks down the contents of the fuel in our stomach before absorbing it through the small intestinal wall lining. Highly processed items such as gels allow this process to occur more rapidly as they are simple molecules that need less processing by our digestive system.
If we have a healthy, uninflamed gut lining, it can absorb this fuel more efficiently. Think of the gut cell walls as a row of balloons that molecules can squeeze past. If these balloons are overfilled (inflamed), then the molecules have difficulty flowing through into our bloodstream and instead can get shuttled straight down the digestive tract to the colon and out the other end. Therefore, building a strong microbiome that protects the gut lining during training (and in general) can help prevent issues on race day.
On top of this, physical and mental stress releases a chemical reaction cascade that is exacerbated by extreme conditions. Add in the physical movement of a sport with its flexing of our gut walls and shaking up the stomach, and it’s no wonder the body can go into full meltdown as it tries to cope with the stress.
One of the mechanisms of our body is it cleverly redirects blood flow to the places it deems most necessary at that moment. During exercise, blood is redirected away from the digestive processes and towards our muscles, heart, and brain. Yet another layer of complexity to the process of digestion during endurance races.
Therefore, review and practice these items:
Ensure the right ratio of fluid to electrolytes.
A balanced intake of carbohydrates in a 2:1 glucose to fructose ratio (more on that below).
Build a healthy gut microbiome for a balanced inflammatory response.
Bonking
When you have a sudden loss of energy and feel nauseous, fatigued, and weak, you are under-fueled. Most athletes think of carbohydrates as fuel for their muscles to keep churning; however, when you bonk, it’s because you’ve starved your brain. The brain needs trace amounts of glucose, and if you’ve miscalculated your carbohydrate needs, your brain can’t access it and begins to shut down.
To help prevent Issues
Again, building a strong microbiome is first a foremost (Prebiotics / Probiotics).
Experiment on practice runs, then follow your usual routine on the day
Consume a warm drink and a little food to get your bowels in order.
Do not introduce any new supplements (e.g., gels) or caffeinated items that you have not practiced with.
Practice your water intake. Know what hydration levels you need, as dehydration can cause digestive issues.
A day or two before the race, reduce your intake of high-fiber and gas-producing foods such as beans, lentils, cruciferous vegetables, bran cereals, etc.
On the day, do a short warm-up to get things moving.
Gut Health
Endurance athletes may reduce GI issues by training their gut to handle high loads of carbohydrate intake during exercise and not incur an over-inflammatory response. Probiotics, prebiotics, and anti-inflammatory foods (e.g., turmeric, ginger) can help build a resilient gut lining. Consuming soluble and insoluble fibers in regular meals can promote overall digestive health.
Individuals who consume probiotic and prebiotic foods may have stronger gut health that can prevent GI issues and discomfort during races. By pre-training your gut with fermented foods and a wide variety of plant-foods to feed them, you may strengthen your microbiome for endurance events.
Include items such as:
Probiotics - yogurt, kefir, kombucha, apple cider vinegar
Prebiotics - A wide variety of fruits and vegetables
Anti-inflammatory - turmeric, ginger, green tea
Healthy fats - extra virgin olive oil, salmon, seeds, nuts
Soluble fibers and Insoluble fibers
Hydration
A general hydration guideline is to consume 2ml of water per kg of body weight every 20 minutes. For a 71kg athlete, this equates to 142ml (~5oz) of water every 20 minutes, or 500ml (~17oz) per hour. However, hydration needs vary based on factors such as sweat rate and environmental conditions. Electrolyte balance is also crucial—overhydration can lead to hyponatremia (low sodium levels), which can cause symptoms similar to dehydration, such as nausea, confusion, and cramping.
To minimize the likelihood of this occurring, you must consciously practice hydration during your training. Be mindful of when you’re drinking, when your thirst cues tend to occur, and calculate what your limits are, both under and over.
Over-hydration
Now, there absolutely is too much of a good thing. If you overhydrate by drinking too much plain water, you are at risk of diluting your electrolytes and throwing your body out of balance. Water toxicity can look like dehydration, with symptoms including nausea, dizziness, vomiting, headaches, confusion, and cramping. Therefore, knowing your personal needs is crucial. Your Client Advocate can work out your ideal hydration range. But you also need to listen to your body during training by testing your upper and lower limits so that on race days, you know how to adjust in the moment. Making sure the ratio of water, carbohydrates, and electrolytes is balanced can help prevent fluctuations in ability.
The American College of Sports Medicine (ACSM) and other sports nutrition organizations recommend a solution percentage of around 8-10%. This means the amount of water to carbohydrate ratio for the average person to stay hydrated, fueled, and prevent digestive issues.
For example: An athlete who is consuming ~500ml (15oz) of water every hour, would need ~43 grams of carbohydrates to maintain that 10% solution in their gut.
However, everyone is different, so you must play around with this percentage to ensure you’re meeting your personal needs. You may find you need higher carbohydrate or water levels.
Carbohydrates / Glucose
Prior to an event:
It is no surprise that carbohydrates are the fuel for extended periods of exercise. Although we can use protein and fat, most bodies are not able to run efficiently on these macronutrients during long periods of extreme stress. And can even be detrimental if you’re not fueling properly, as the body may pull from other vital areas like our muscles. Practicing your fueling strategy during training is the best way to optimize and understand your needs prior to the main event.
Whether training for your first or fiftieth endurance event, you should always be perfecting your routine if you want to keep improving your time and reduce your injury risk. For some, oats and raisins feel good, but for others, yogurt and bananas are the fuel they need to start their run. Perfecting your nutrition program with the help of Apeiron Life nutrition advisors can mean the difference between a sub-three-hour marathon or bonk-ing out halfway.
The Week Before a Race
The idea that a big ol’ bowl of pasta the night before will suffice has been shown lacking. Ideally, the entire week prior to an event, you should be carboloading with nutrient-dense complex carbs (like sweet potato, oats, quinoa, and brown rice) and slowly decrease the amount of fiber until a couple of days prior to the event. This strategy may help build up your glycogen stores and may postpone muscle fatigue.
The International Society of Sports Nutrition for high endurance sports like ultramarathon running suggests around 5-12g/kg/bw/day.
Day of the event:
On the day of the race, you will be having your breakfast two to three hours before the event. Therefore, partitioning your meals into focused sections can be beneficial. For your first meal, aim for 30-60g of easy-to-digest carbohydrates. And then again an hour prior to the event, such as a banana. For the most part, avoid high insoluble fibrous foods or high protein items (but they are important post-training and on rest days).
For breakfast, items such as:
Whole wheat toast with peanut butter, sliced banana, and honey.
Smoothie with oatmeal, banana, turmeric, and maple syrup.
Oatmeal or rice pudding with blueberries and honey.
Sweet potato with greek yogurt.
During the event:
We reduce our carbohydrate stores at a rate of ~1.2g/min CHO ingested. For a marathon, athletes should consume 20g of carbohydrates every 20 minutes (~60g per hour). This can be achieved through gels, drinks, or whole foods, depending on personal preference and tolerance. Some athletes may benefit from consuming up to 100g of carbohydrates per hour, depending on their training and metabolic rate.
You can consume the gel in one go, or spread it out into halves or thirds, depending on what feels best for you.
For a Marathon -The gel brand Maurten Recommends timing splits with fueling based on their five (GEL160) to seven (GEL100) GELs in total - or 175-200g of carbohydrate:
Sub 2:30 = 3:33 min/km = 70-80 g/h = 1x every 20 min
Sub 3:00 = 4:16 min/km = 58-67 g/h = 1x every 25 min
Sub 3:30 = 4:59 min/km = 50-57 g/h = 1x every 30 min
Sub 4:00 = 5:40 min/km = 44-50 g/h = 1x every 35 min
Sub 4:30 = 6:24 min/km = 39-44 g/h = 1x every 40 min
Whichever brand you choose, be aware of any fillers, preservatives, or sweeteners that may be detrimental to you. And understand the basics of different carbohydrates to choose the ones that work best for your body. Different combinations of carbohydrates are used in gels, bars, and other endurance fuels.
Glucose: Fructose Ratio (g:f)
A 2:1 ratio of glucose to fructose (g:f) is ideal for maximizing carbohydrate absorption and preventing GI issues. Combining glucose (quick energy) with fructose (sustained energy) allows the body to utilize different transporters in the gut, improving total carbohydrate uptake (ACSM). For example, honey has a ~3:4 glucose-to-fructose ratio, while maple syrup has a balanced 1:1 ratio.
Sugar Mixtures (Combination of Glucose and Fructose)
Sucrose (Sugar) = 50:50 ratio of g:f
High Fructose Corn Syrup (HFCS) = A syrup made from corn.
~50:50 g:f
Maple syrup = 50:50 g:f, but with some other stuff in it.
Maple Syrup single-serve packets
Honey = 3:4 g:f. The reversed ratio of a lower glucose amount means this sweetener may not be best for endurance sports. Avoid, unless mixing with a fructose product.
Maltodextrin = A processed complex carbohydrate, typically derived from corn, wheat, potato, or rice. It is chains of glucose molecules that are then broken down to make it more easily digestible.
Pure glucose, therefore often mixed with a fructose sweetener to balance the ratio.
Tapioca syrup = A syrup made from cassava. A complex carbohydrate formed of chains of glucose molecules.
Pure glucose, therefore often mixed with a fructose sweetener to balance the ratio.
Items that adhere to the 2:1 ratio:
Gels - SiS GO Isotonic Energy Gel / Maurten GEL 100 / TORQ Energy Gel
Blocks - Clif Bloks Energy Chews / GU Energy Chews
Bars - PowerBar PowerGel Hydro Energy Bar / SIS Energy Bars
When it comes to choosing a brand, there is a wide variety of items that utilize different carbohydrate sources. It is, therefore, extremely important to test and train with different formulas to see what works best for you.
Hydrogels vs. Traditional Carbohydrate Sources
Research comparing hydrogels and traditional carbohydrate sources in endurance sports has produced mixed results. Hydrogels, such as those found in products like Maurten gels, encapsulate carbohydrates in a gel matrix, which is designed to reduce gastrointestinal distress and enhance carbohydrate absorption.
Although there is not a large amount of research or information available to the public. One paper did show beneficial GI symptoms and performance compared to a standard carbohydrate solution. However, this was one study and it did not compare to other options such as blocks, traditional gels, whole foods, or other possible fueling options.
Other studies (1, 2) showed that the current evidence does not suggest a difference between hydrogels and traditional carbohydrate sources. The current evidence suggests that hydrogels may be beneficial for athletes prone to GI issues, but overall performance gains remain similar to traditional carbohydrate sources.
Caffeine
Abstaining from caffeine for 4 days before the event may help habitual caffeine users maximize its performance-enhancing effects on race day. A dose of 2-6mg/kg of body weight (e.g., ~142mg for a 71kg athlete) consumed 30 minutes before the race can improve performance without overdoing it. However, excessive caffeine (>5mg/kg) may negatively impact some people's performance. For those who are habitual caffeine drinkers, the effects may not have the same impact, and higher doses may be required. Or taking a break from caffeine for a few weeks prior to a race may help decrease tolerance. Caffeine can boost endurance and focus. However, it’s essential to experiment with caffeine in training to ensure it does not cause GI distress or other side effects during the race.
After the event
To recover from muscle damage, you want to be consuming around 1.5g carbohydate per kg of bw. For example, at 71kg bw, you’ll want to consume ~100g of carbohydrates. For higher output events, you may want to increase this to almost double, and for lower expenditure events, you can reduce this to almost half. Work with your dietitian to find the right balance for you.
Protein
Protein is not for during your race. It is for training purposes and after the race. It is a crucial component of building your muscles and preventing them from breaking down. Other items that can assist the process of muscle building include creatine monohydrate (link) and ensuring you’re consuming a full Amino Acid profile (link). However, protein is not an area to focus on during the race.
For training purposes, the timing of protein has mostly been overemphasized. Rehydrating and protein intake after a workout is vital; however, the time frame has been shown to be wider than previously thought. At one point, the theory that consuming protein within a 30-minute window after a workout was necessary has been disproven, and total intake throughout the day should be your focus. Aim for around ~1.6 g/kg/bw.
Our take:
It is crucial to understand your particular fueling needs. Practicing different nutrition strategies, maintaining a healthy gut microbiome, and fine-tuning hydration can prevent gastrointestinal (GI) issues and energy depletion during races. Key factors to consider include the right balance of fluids and electrolytes, carbohydrate intake with a preferred 2:1 glucose-to-fructose ratio, and maximizing simple carbohydrate intake leading up to the event to enhance glycogen stores. Our Apeiron Life nutrition advisors can suggest items based on your history and personalize your program to your needs.
Still curious to try it? If you do, here’s what to keep an eye on:
Watch for bloating, cramping, diarrhea, or nausea. If you experience any discomfort, consider adjusting the type, timing, or amount of fuel.
Track how you feel during and after workouts. Are you experiencing sustained energy, or do you feel fatigued or “bonked”?
Pay attention to your thirst cues and ensure you’re adequately hydrating. Consider how the new fuels impact your hydration (some may be more dehydrating).
Monitor how your body reacts to the fuel in terms of energy spikes and crashes. This can help you find a more stable source. If possible, check your blood sugar levels pre- and post-consumption to assess the impact.
References and additional reading:
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