The question of what percentage of an athlete's energy intake should be carbohydrates is complex, with the answer being far from a single, fixed number. While general recommendations for the public suggest 45–65% of calories from carbohydrates, an athlete's needs are highly specific and fluctuate based on training volume and intensity. High-intensity and prolonged exercise depletes muscle and liver glycogen stores, making carbohydrates the most critical macronutrient for fueling and recovery.
Carbohydrates vs. The 'Percentage' Myth
Many nutrition experts argue that focusing on a percentage can be misleading for athletes. A percentage does not account for an athlete's body mass or varying daily energy needs. For instance, a smaller athlete and a larger athlete might both aim for 60% carbohydrates, but their total gram intake—and thus their actual fuel stores—would be vastly different. A 70kg athlete training moderately (5-7 g/kg/day) needs significantly fewer total carbohydrates than a 90kg athlete engaged in extreme endurance training (8-12 g/kg/day). Therefore, grams per kilogram of body weight is a more precise and functional metric for athletes to follow.
The Importance of Glycogen Stores
Carbohydrates are the body's most efficient fuel source for high-intensity exercise. When consumed, they are converted into glucose and stored as glycogen in the muscles and liver. During intense activity, the body rapidly taps into these glycogen reserves for energy. When stores are low, performance suffers and the body may resort to less efficient fuel sources, like fat, which can only be burned at a lower intensity. Consistent underfueling can lead to a condition known as Relative Energy Deficiency in Sport (REDs), causing impaired performance, injury, and other serious health issues.
Periodizing Carbohydrate Intake
A modern, evidence-based approach is to 'periodize' carbohydrate intake, adjusting it to match the demands of training. On high-intensity, long-duration training days, an athlete's carbohydrate requirements are significantly higher to ensure sufficient fuel. Conversely, on rest days or during periods of low-intensity exercise, intake can be scaled back. This strategic fueling helps maintain energy balance, optimize recovery, and support adaptation to training.
Comparison: Carbohydrate Needs by Activity Level
| Activity Level | Daily Carbohydrate Intake (g/kg of body weight) | Example Training Type |
|---|---|---|
| Light | 3–5 g/kg/day | General fitness, casual workouts <1 hour |
| Moderate | 5–7 g/kg/day | 1–3 hours of moderate intensity daily |
| Endurance | 7–10 g/kg/day | 1–3 hours of high-intensity endurance daily |
| Extreme Endurance | 8–12 g/kg/day | 4+ hours of intense training daily |
Fueling Before, During, and After Exercise
Pre-Exercise Fueling
Eating carbohydrates before exercise is vital to top off liver and muscle glycogen stores. The timing and type of carbohydrate depend on the proximity to the workout. For a long event, a larger meal 3-4 hours prior containing 1-4 g/kg of carbs is ideal. As the event nears, smaller, easier-to-digest carbs can be consumed.
During Exercise Fueling
For activities lasting over 60 minutes, carbohydrate intake is crucial to maintain performance and delay fatigue. Recommendations vary with duration:
- 45–75 minutes: Small amounts or a carb mouth rinse.
- 1–2 hours: 30–60 g per hour.
- 2–3 hours: 60–90 g per hour, often using multiple transportable carbs (glucose and fructose).
- >2.5 hours (Ultra-endurance): Higher intakes may be tolerated, up to 120 g/h with specific carbohydrate blends, but practice is essential to avoid gastrointestinal issues.
Post-Exercise Recovery
Post-workout nutrition is critical for replenishing glycogen stores, especially with multiple training sessions per day. Consuming 1.0–1.2 g/kg of body weight of high-glycemic carbohydrates within the first few hours post-exercise, often combined with protein, is recommended to maximize glycogen resynthesis.
Conclusion: Personalize Your Approach
While initial percentage-based guidelines (e.g., 45–65%) can serve as a starting point, they are insufficient for the nuanced needs of athletes. The modern and more accurate approach is to calculate carbohydrate requirements based on grams per kilogram of body weight, adjusted for the specific demands of training and competition. By periodizing intake around exercise, an athlete can optimize performance, accelerate recovery, and avoid the health risks associated with underfueling. Finding the right balance requires self-experimentation with different carbohydrate sources and timing, a strategy that is best honed through careful practice during training.
For more detailed guidance on endurance fueling, visit the Gatorade Sports Science Institute website.
