Why Athletes Eat High Carbohydrate Foods Before a Competition

December 17, 2025 •

3 min read

According to the International Society of Sports Nutrition, a high-carbohydrate diet is crucial for maximizing endogenous glycogen stores in athletes. This is precisely why athletes eat high carbohydrate foods before a competition, fueling their muscles and liver to sustain high-intensity, prolonged exercise and delay fatigue.

Quick Summary

Athletes consume high-carbohydrate meals before a competition to top off their glycogen stores, providing the primary fuel source for high-intensity or endurance-based exercise. This delays fatigue, boosts energy availability, and supports peak performance by ensuring muscles have sufficient fuel for the duration of the event.

Key Points

Maximizing Glycogen: High-carbohydrate intake replenishes and maximizes the body's glycogen stores in muscles and the liver, which are the main energy reserves for exercise.
Delaying Fatigue: Full glycogen stores ensure that muscles have enough fuel to perform during prolonged, high-intensity exercise, preventing the premature onset of fatigue.
Carb-Loading Strategy: For endurance events, athletes use a 'carb-loading' technique in the 1-3 days before competition, increasing carbohydrate intake while tapering training volume.
Timing is Crucial: Pre-competition meals are carefully timed (e.g., 3-4 hours before) to provide readily available energy for the event's start, while small, simple carb snacks are used closer to the start.
Avoiding High Fat/Fiber: Athletes avoid high-fat and high-fiber foods before a competition to prevent digestive discomfort and ensure carbohydrates are the focus for energy.
Personalized Approach: The optimal fueling strategy depends on the athlete and sport, requiring practice during training to find the right approach and minimize digestive issues.

The Science of Carbohydrates and Athletic Performance

Carbohydrates are the body's primary and most efficient energy source, converted into glucose and stored as glycogen in the liver and muscles. During intense physical activity, particularly endurance events, the body burns through its glycogen reserves to produce adenosine triphosphate (ATP), the cellular energy currency. A depletion of these stores is a major cause of fatigue, leading to a significant drop in performance.

By consuming high-carbohydrate foods in the hours or days leading up to a competition, athletes practice what is known as carbohydrate-loading or "carb-loading". This strategy aims to super-compensate the body's glycogen levels, effectively creating a larger "fuel tank" that can sustain the athlete through the duration of their event without hitting a performance-limiting wall. This is particularly critical for sports lasting 90 minutes or longer, such as marathons, long-distance cycling, or soccer tournaments, where energy demands are extremely high.

The Importance of Timing and Type of Carbohydrate

The timing and type of carbohydrates consumed are just as important as the quantity. The pre-competition nutrition strategy often involves a multi-stage approach, starting several days out and continuing until just before the event.

Strategic Carbohydrate Timing for Athletes

48-72 hours before: A shift to a high-carbohydrate diet, often around 8–12 grams per kilogram of body weight per day, combined with a reduction in training volume (tapering), maximizes muscle glycogen stores.
3-4 hours before: A pre-event meal focused on easily digestible carbohydrates ensures the body has readily available energy for the initial stages of the competition. This is enough time for digestion without causing a heavy, full feeling during the event.
1 hour or less before: A smaller, simple carbohydrate snack (e.g., a sports gel or rice cakes) provides an immediate energy boost, maintaining blood glucose levels as the competition begins.

It's also important for athletes to consume a mix of simple carbohydrates (for quick energy) and complex carbohydrates (for sustained release) at different points in their pre-competition fueling plan.

Why Not Other Macronutrients?

While protein and fats are essential for an athlete's diet, they are not the ideal primary fuel source for performance, especially not immediately before a competition.

Carbohydrate vs. Fat/Protein as Fuel


Macronutrient	Primary Role in Performance	Pre-Competition Consideration	Why Not Optimal for Immediate Fueling
Carbohydrates	Primary energy source, converted to glucose and stored as glycogen.	Essential for maximizing fuel reserves and delaying fatigue.	Provides quick, efficient, and sustained energy for performance.
Fats	Secondary energy source for low-to-moderate intensity exercise.	Avoid high-fat meals close to competition.	Take significantly longer to digest, causing sluggishness and stomach upset during exercise.
Protein	Primarily for muscle repair and recovery, not a significant fuel source.	Necessary for muscle repair in the overall diet, but not the focus of a pre-competition meal.	The body uses protein for energy only when other fuel sources are depleted, a process that is inefficient and can lead to muscle breakdown.

Practicing Your Pre-Competition Fueling Strategy

Athletes are advised to practice their carbohydrate-loading and pre-event eating strategies during training to test how their body responds and to avoid any gastrointestinal distress on game day. This personalized approach, often guided by a sports dietitian, ensures the strategy is optimized for the specific athlete, their sport, and the event's duration.

Conclusion: Fueling for Peak Performance

Ultimately, the practice of consuming high-carbohydrate foods before a competition is a scientifically-backed strategy designed to optimize athletic performance by maximizing energy stores. This ensures the athlete's body has the necessary fuel to perform at its peak for the entire duration of the event, pushing past the point where fatigue would otherwise set in. Strategic fueling isn't just about eating a plate of pasta; it's a carefully timed and tailored plan to give athletes a decisive edge.

An excellent resource for further reading on the science of sports nutrition is the International Society of Sports Nutrition position stand on nutrient timing: International society of sports nutrition position stand: nutrient timing.

Frequently Asked Questions

The primary reason is to maximize the body’s glycogen stores, which serve as the main fuel source for muscles during intense or prolonged physical activity, thereby delaying fatigue and boosting performance.

Carb-loading is a dietary strategy used by endurance athletes (e.g., marathon runners, long-distance cyclists) in the days leading up to an event to maximize muscle glycogen storage. It is most beneficial for activities lasting 90 minutes or longer.

Athletes should consume a mix of complex carbohydrates (like whole grains and pasta) and simple carbohydrates (like fruit or sports gels) at different intervals before an event to provide both sustained and immediate energy.

A substantial pre-event meal should be eaten approximately 3-4 hours before a competition to allow for proper digestion. A smaller, simple carbohydrate snack can be consumed closer to the event, like 30 minutes to an hour beforehand.

High-fat foods should be avoided before a competition because they take a long time to digest and can cause stomach upset, sluggishness, and digestive issues during exercise.

No, carb-loading is most effective for endurance athletes in long-duration events. For shorter-duration, high-intensity sports, sufficient daily carbohydrate intake is typically enough.

Insufficient carbohydrate intake can lead to depleted glycogen stores, resulting in premature fatigue, a decrease in training intensity, and a significant drop in performance.