Carb Loading: Science-Backed Strategies for Peak Performance

Hi there! I'm Rebekah, a Registered Dietitian, Certified Diabetes Educator and Certified Intuitive Eating Counselor specializing in Performance Nutrition. I help athletes of all ages and abilities fuel their bodies optimally for sport and...whatever else life throws at them! I practice nutrition therapy from an evidence-based & weight-neutral approach, focusing on fueling the body for strength, power and health instead of specific number on the scale. Today, we are tackling something that was certainly relevant to me recently. This past weekend I competed in my first Olympic length triathlon!

In order to properly prepare my body, I did 2 days of carbohydrate loading. Let's talk about what this is, why it helps, and how to go about it!

Introduction

Now this was a bit different for me - many of my previous athletic experiences have been for events around 1.5 hours (e.g my half marathon this past spring), or shorter events such as swim meets, 5-10km runs, or a sprint triathlon. I was aiming for a time between 2.5-3 hours for this race...so you can say it's a bit of a jump in distance!

For athletes tackling endurance events lasting longer than 90 minutes—marathons, long triathlon legs, bike races, cross-country ski races—carbohydrate loading (“carb loading”) can meaningfully delay fatigue, sustain power, and maintain efficient mechanics.

Why Carb Loading Works

Starting an event with elevated glycogen stores can delay fatigue and maintain performance. Glycogen depletion strongly correlates with exhaustion in prolonged exercise, making carbohydrate availability crucial (Thomas et al., 2016). The carb-loading approach ensures muscles have the maximum “fuel tank” available before competition.

How Much to Eat and When

Modern carb-loading strategies are straightforward and effective. Athletes should aim for 8–12 g carbohydrate per kilogram body mass per day for the 24 - 48 hours before competition (Kerksick et al., 2017; Thomas et al., 2016).

Notably, older “deplete then load” models are no longer necessary. Research shows glycogen stores can be maximized with just one to two days of high-carbohydrate intake paired with reduced training (Jeukendrup, 2017). This approach is easier, less stressful, and equally effective.

Pre-Race Meal Timing & Composition

The pre-race meal (1-4 hours before start) should provide 1-4 g/kg carbohydrate from familiar, low-fiber, low-fat foods. Athletes prone to pre-race nerves may tolerate liquid carbohydrate sources - smoothies or sports drinks - better (Kerksick et al., 2017).

Timing matters: ingesting carbohydrate too close to the start may, in some, cause transient dips in blood sugar. A brief warm-up or consuming carbohydrate about 15 minutes pre-race helps avoid this (Jeukendrup, 2017).

During-Race Fueling

Carb loading tops up the tank, but during-race fueling keeps it from emptying. For 2–4 hour events, the consensus is 30-60 g carbohydrate per hour, ideally from multiple sources (e.g., glucose + fructose) to improve absorption and oxidation (Kerksick et al., 2017; Jeukendrup, 2017). Small, frequent intakes every 10-15 minutes reduce gut discomfort and support steady energy.

The joint position paper from the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine confirms carbohydrate loading improves endurance performance and recommends athletes follow evidence-based intake ranges (Thomas et al., 2016). The International Society of Sports Nutrition echoes these recommendations in its nutrient timing position stand, reinforcing the importance of both pre-race glycogen maximization and in-race fueling (Kerksick et al., 2017).

Here is an example of what I did to reach my carbohydrate needs:

24-48 h pre-race

• 455-680 g CHO/day (≈8-12 g/kg/day).

• Spread across 5-6 meals/snacks: pasta, rice bowls, bagels, low-fiber cereals, pretzels, fruit juice.

Race morning (3 h pre-start)

• ~60-224 g carbohydrate: e.g., bagel w/ peanut butter, 1/2 cup chocolate milk, bear paw

30-60 minute pre-start

• ~60-120g carbohydrate: e.g., tangerine/banana, fruit gummies

During race

• ~30–60 g carbohydrate/hour: gels, chews, or sports drink.

Example day of carb loading:

Breakfast	1 cup oatmeal, 1 pear, 2 tbsp maple syrup, 1 cup chocolate milk	119g carbohydrate
AM Snack	Granola bar, 1 cup juice	50g carbohdyrate
Lunch	2 cups ravioli pasta, 2 cups juice	114g carbohdyrate
PM Snack	Bear Paw, 1 cup chocolate milk	60g carbohydrate
Supper	2 cups rice, ground chicken, vegetable stir fry	90g
Night snack	1 cup juice	30g carbohydrate	Total carbohydrate:463g

Common Pitfalls & Fixes

Mistake	Fix
Eating too much fiber or fat pre-race	Stick to refined carbs and lighter sauces.
Underestimating carbs	Track or pre-plan your intake to ensure you reach 8-12 g/kg/day.
Trying new foods on race week	Rehearse carb loading in training.
Thinking carb loading replaces in-race fueling	Plan for 30–60 g/hr carbs during the event.

Carb Loading for Shorter Events: Is It Worth It?

Carbohydrate loading has clear benefits for endurance events lasting longer than ~90 minutes, but what about shorter races - like a 10 km run, sprint triathlon, or a 60–90 minute hockey game?

What the Evidence Says

• Events <90 minutes: Studies show no consistent performance benefit from carbohydrate loading in shorter, high-intensity events. Glycogen stores are usually sufficient to fuel performance without “supercompensation” (Thomas et al., 2016; Kerksick et al., 2017).

• Events ~90–120 minutes: Benefits are mixed. Some endurance athletes may gain a small edge from starting with elevated glycogen, particularly if they go hard from the gun. But the effect size is smaller than in 2–4 hour events (Jeukendrup, 2017).

• Key point: For shorter events, topping up glycogen is useful, but a normal balanced high-carbohydrate diet (≈5–7 g/kg/day) in the days before competition is usually enough. You may not need the full 8–12 g/kg/day carb-loading protocol.

Practical Guidance

• Focus on a pre-race meal (1-4 g/kg carbohydrate, 1-4 hours before the start). This ensures liver glycogen is replenished after the overnight fast and provides easily available fuel.

• During-race fueling is not typically necessary unless the event approaches the 90-120 minute mark. A small sip of sports drink or a single gel may help psychologically and physiologically in the latter stages.

• Gut comfort matters - avoid overloading the system with unnecessary carb-loading meals that may cause bloating or GI distress in shorter races.
  

  

Bottom Line

For short events (<90 min), carb loading is not required - just eat normally with adequate daily carbs (≈5–7 g/kg/day) and include a solid pre-race meal. For events close to 2 hours, a moderate bump (≈7–10 g/kg/day) in the 24 hours prior may provide a small benefit, especially if the athlete expects a fast, aggressive pace.

Final Thoughts

Carbohydrate loading for endurance events is not about gimmicks—it’s about proven strategies. Focus on 8–12 g/kg/day carbs in the 24–48 hours before competition, a 1–4 g/kg pre-race meal, and 30–60 g/hr during the event. Test your fueling in training to fine-tune what works best for your body, and you’ll line up confident, fueled, and ready.

References (APA 7th edition)

Jeukendrup, A. E. (2017). Training the gut for athletes. Journal of the International Society of Sports Nutrition, 14(1), 47. https://doi.org/10.1186/s12970-017-0189-4

Kerksick, C. M., Arent, S., Schoenfeld, B. J., Stout, J. R., Campbell, B., Wilborn, C. D., Taylor, L., Kalman, D., Smith-Ryan, A. E., Kreider, R. B., Willoughby, D., Arciero, P. J., VanDusseldorp, T. A., Ormsbee, M. J., Wildman, R., Greenwood, M., Ziegenfuss, T. N., Aragon, A. A., Antonio, J., & Kreider, R. (2017). International society of sports nutrition position stand: Nutrient timing. Journal of the International Society of Sports Nutrition, 14(1), 33. https://doi.org/10.1186/s12970-017-0189-4

Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528. https://www.dietitians.ca/DietitiansOfCanada/media/Documents/Resources/noap-position-paper.pdf