The Fourth Discipline: Mastering Race Day Fueling in Practice
- rdcdietitian
- Aug 12
- 4 min read
Hi there! I'm Rebekah, a Registered Dietitian, Certified Intuitive Eating Counselor, and Certified Diabetes Educator specializing in sport nutrition. I live and work in Ottawa, Ontario, Canada. This beautiful city I call my home just hosted it's first Ironman race. Unfortunately, I have seen a few folks speaking of negative experiences during the race due to a dislike (or intolerance) of the on-course hydration or nutrition provided. As a sport dietitian, I wanted to speak to this briefly - specifically, the importance of NOT relying on the on-course fueling - unless you have investigated and practiced with it!
One of the most overlooked aspects of race preparation is training your gut. It's actually considered by many to be the fourth discipline. I’ve seen athletes dedicate months to perfecting their fitness, only to have their performance derailed by dehydration, hitting the dreaded “wall,” or gastrointestinal (GI) distress on race day. The solution? Practice your fueling strategy in training, just like you practice your pacing.
Why Practice Matters
Your gastrointestinal tract is adaptable. When you repeatedly fuel during training, you improve your body’s ability to absorb carbohydrates, tolerate fluids, and handle the mechanical stress of digestion while moving. Without this practice, your gut is more likely to rebel during competition - resulting in cramping, bloating, nausea, vomiting or urgent bathroom stops.
Research shows that practicing your fueling strategy in training can improve carbohydrate oxidation rates and reduce GI symptoms during competition (Costa et al., 2017). This is critical in endurance events, where fueling mistakes can mean the difference between a strong finish and a disappointing DNF.
Key Race Fueling Strategies
1. Hydration
Hydration is more than just drinking when you’re thirsty. Fluid losses from sweat can lead to dehydration, impairing performance and increasing the risk of heat-related illness.
General guideline: Replace 60-80% of fluids lost or 400-800ml of fluids per hour. This greatly depends on the individual and how much they sweat. You can get an idea of your individual sweat rate by taking a pre and post-training weight. Every kilogram lost is equivalent to about 1L of sweat loss that needs to be replaced.
In recovery, aim to replace 150% of fluid lost. For example - if you lost 1kg of body weight during exercise, you should aim to consume 1.5L of fluids to properly recover.
Electrolytes: Include sodium (300–800 mg/L) in your fluids to help retain water and maintain electrolyte balance. Everyone's electrolyte losses in sweat are different. There are ways to test your sweat sodium concentration but without this, I recommend people trial different electrolyte concentrations to see what works best for them.
2. Carbohydrate Fueling
Endurance events lasting more than 90 minutes rely heavily on carbohydrate availability. Depleted glycogen stores can lead to fatigue and performance decline.
Evidence-based recommendation: 30–60 g carbohydrate/hour for events up to 2.5 hours; 60–90 g/hour for longer events, ideally from multiple transportable carbohydrates (glucose + fructose) to maximize absorption (Burke et al., 2011).
Practice tip: Experiment with several different carbohydrate foods, sports gels, chews, or drinks during long training sessions to find the products, flavors, and textures your gut tolerates best.
Don't forget about simple, yet effective 9and budget-friendly) carbohydrate foods such as fruit gummies, applesauce, cereals, stroopwaffles, or even a favourite candy. And...before you say it - yes there are added sugars in many of those foods. They are a tool for performance fueling. If you'd like to learn more about how sugar is used as a tool in sport nutrition, take a look at a previous post of mine here.
3. Managing Gastro Intestinal (GI) Discomfort
GI distress is common in endurance athletes, but it’s not inevitable. Factors that increase risk include excessive fiber, fat, or protein intake too close to competition, as well as high-concentration carbohydrate drinks (>8% solution).
Training the gut: Gradually introduce carbohydrate intake during long workouts, starting at the lower end (30g) of recommendations and increasing over several weeks.
Avoid surprises: On race days, stick with the same products and timing you’ve practiced during training - race day is not the time to try something new.
Putting It All Together
Think of your fueling plan as a fourth discipline in endurance sport, alongside training, recovery, and mental preparation. Schedule “nutrition dress rehearsals” during long runs or rides. Document what you ate, drank, and how you felt, then adjust accordingly.
On race day, your fueling strategy should feel second nature - something you’ve practiced, refined, and trusted. That preparation allows you to focus on your performance, not your stomach.
If you need help navigating sport nutrition, connect with me and let's get working towards your health and performance goals.
If your team is looking for nutrition support, check out Built to Perform for services tailored for team nutrition. From educational workshops to training camp and competition support, we've got your nutrition needs covered!
References:
Costa, R. J. S., et al. (2017). Systematic review: Exercise-induced gastrointestinal syndrome—implications for health and intestinal disease. Alimentary Pharmacology & Therapeutics, 46(3), 246–265.
Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 2011;29 Suppl 1:S17-27. doi: 10.1080/02640414.2011.585473. Epub 2011 Jun 9. PMID: 21660838.
Sawka, M. N., et al. (2007). American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377–390.
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