Carbohydrates are the body's preferred fuel source during high-intensity exercise, storing as glycogen in muscles and the liver. Depleting these stores is a primary cause of fatigue, often referred to as 'hitting the wall'. Proper fueling is essential for training adaptations, race performance, and recovery.
Daily Carbohydrate Needs for the Endurance Athlete
Your daily carbohydrate intake should be periodized, meaning it varies with the volume and intensity of your training.
- Low-intensity/skill-based days: 3–5 grams per kilogram (g/kg) of body weight. A 70 kg athlete would need 210–350g.
- Moderate-intensity (1 hour/day): 5–7 g/kg. A 70 kg athlete would need 350–490g.
- High-intensity (1–3 hours/day): 6–10 g/kg. A 70 kg athlete would need 420–700g.
- Extreme training (>4 hours/day) or competition: 8–12 g/kg. A 70 kg athlete would need 560–840g.
These needs are a starting point; individual tolerance and goals must be considered.
Fueling Before, During, and After Your Event
Pre-Competition Carb Loading
For endurance events lasting over 90 minutes, carbohydrate loading can boost muscle glycogen stores by 30% or more. The strategy involves increasing carb intake 1–3 days before the event.
- Two-Day Plan: Aim for 10–12 g/kg of carbs per day. For a 70 kg athlete, this means 700–840g daily. Focus on low-fiber, easily digestible carbs like white rice, pasta, and potatoes to avoid gastrointestinal issues.
- Morning of the Event: Consume 1–4 g/kg of carbs 1–4 hours before the race to top off liver glycogen stores. A light breakfast with toast, jam, and a sports drink is a good option.
Carbohydrate Intake During Exercise
Fueling during the event is critical to maintain blood glucose and spare glycogen.
- 45–75 minutes: Small amounts or a mouth rinse can enhance performance.
- 1–2.5 hours: 30–60 grams of carbohydrates per hour. A sports drink or gel is an effective strategy.
- >2.5 hours: 60–90 grams of carbohydrates per hour. For intakes over 60 g/h, using a multiple transportable carbohydrate source (e.g., glucose and fructose mixture at a 2:1 or 1:0.8 ratio) is recommended to maximize absorption and reduce stomach upset. Some ultra-athletes may tolerate up to 120 g/h.
- Ultra-Endurance (>6 hours): Beyond 90 g/h, some athletes push limits with glucose-fructose mixes. Adding small amounts of protein and fat from real foods can also be beneficial.
Post-Exercise Recovery
Replenishing glycogen stores quickly is key for rapid recovery.
- Immediate Post-Exercise: Consume 1.0–1.2 g/kg of high-glycemic carbohydrates within the first 4 hours after exercise. Spreading this over smaller, frequent feedings is effective.
- Long-Term Recovery: Resume your daily carbohydrate intake based on your training load.
Low Carb vs. High Carb for Endurance: A Comparison
Some athletes explore low-carb strategies, but science suggests they are not optimal for peak performance at high intensity.
| Feature | High-Carb Approach | Low-Carb (Keto) Approach |
|---|---|---|
| Primary Fuel Source | Glycogen and blood glucose. | Fat stores and ketones. |
| Performance at High-Intensity | Superior; carbs fuel anaerobic and high-power efforts. | Impaired; fat metabolism is slower, limiting high-intensity output. |
| Training Adaptation | Optimizes ability to use carbs. Can include 'train low, race high' strategies for metabolic flexibility. | Increases fat oxidation rates and mitochondrial biogenesis. |
| Recovery | Enhanced; faster glycogen resynthesis. | Impaired; slower glycogen recovery. |
| Glycogen Stores | Maximized. Essential for high-power output. | Lower, which can compromise performance in prolonged intense exercise. |
| Cognitive Function | Stable blood glucose prevents mental fatigue and poor concentration. | Risk of reduced concentration, especially during prolonged, intense efforts. |
Customizing Your Fueling Strategy
Every athlete is different. The ideal fueling plan is personal and requires practice during training. Factors like gut tolerance, gender, and environmental conditions can impact your needs. Training your gut to tolerate high carbohydrate loads is a known strategy to prevent gastrointestinal distress on race day. Female athletes may utilize fats more efficiently and have altered glycogen needs depending on their menstrual cycle. Working with a sports nutritionist can help tailor a plan to your specific physiological needs and competition demands.
Conclusion
To maximize endurance performance, athletes must prioritize carbohydrates by aligning intake with training demands. This involves ensuring adequate daily carbs for training, executing strategic carb loading for key events, consuming precise amounts during prolonged exercise, and rapidly replenishing stores for recovery. While daily intake can range from 3–12 g/kg, during-event fueling typically falls between 30–90 g/h, often using multiple carbohydrate sources for optimal absorption. Relying on a low-carb approach is generally not recommended for high-performance endurance, as it can hinder high-intensity efforts and recovery. Personalizing your strategy, including training your gut, is the final key to unlocking your peak endurance potential.
What are some good carbohydrate sources for endurance athletes?
- During Exercise: Sports drinks, energy gels, sports chews, bananas, dried fruit, white bread.
- General Fueling/Recovery: Whole grains, starchy vegetables (potatoes, sweet potatoes), rice, pasta, oatmeal, fruits, dairy.
How can I practice my race-day fueling plan?
- Train your gut by practicing your fueling strategy during long training sessions.
- Start with lower carb amounts and gradually increase your intake to build tolerance.
- Test different food types and brands to find what works best for you.
- Practice eating and drinking at race pace to simulate race day conditions.
