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Carbohydrate Loading Before an Endurance Race: The Modern, Evidence-Based Protocol for 2026

For years, "carb loading" before an endurance event conjured up an image of eating a mountain of pasta the night before race day. But the updated 2026 recommendations — drawn from new research in Sports Medicine, the Journal of Applied Physiology and the ISSN/ACSM consensus positions — show that effective carb loading is far more sophisticated and individualized, built around three pillars: pre-race loading, in-race fueling, and training your gut to absorb more.

1. The pre-race carb loading protocol

Unlike the old belief in a "depletion phase" followed by a loading phase, current guidance no longer requires a period of carb restriction beforehand. Specifically:

• Load 8–12 g of carbohydrate per kg of body weight per day for 1–2 days before the race (a 70 kg athlete, for example, needs roughly 560–840 g of carbs per day).
• No "glycogen depletion" phase is needed before loading.
• Expect a temporary gain of about 1–2 kg (2–4 lbs) from stored glycogen and water — this is normal, not "fat weight."
• Pre-start meal: 1–4 g of carbs per kg, eaten 1–4 hours before the start, favoring low-fiber foods to reduce digestive discomfort.

2. In-race carb intake by duration

Your fueling rate during the race should match the intensity and duration of the event, rather than applying one fixed number to every distance:

• Under 45 minutes (5K, sprint triathlon): water only, no carb intake needed.
• 45–75 minutes (10K, Olympic triathlon bike leg): about 30 g/hour.
• 75 minutes–2 hours (half marathon, Olympic triathlon): 30–60 g/hour.
• 2–4 hours (marathon, half-Ironman): 60–90 g/hour.
• Over 4 hours (Ironman, long road cycling): 80–120 g/hour.
• Ultra-endurance 6+ hours (UTMB-style): usually settles around 60–90 g/hour.

Notably, research by Wilson (2025, Sports Medicine) concluded the current evidence "does not clearly support" intakes above 90 g/hour in real race conditions, even though elite athletes (such as the pro peloton) now take in 120 g/hour or more. Another study by Ravikanti and colleagues (2025, Journal of Applied Physiology) in elite marathoners found that 120 g/hour reduced oxygen cost by 3.6% compared with 60 g/hour, but was not significantly different from 90 g/hour — while gastrointestinal symptoms were highest at 120 g/hour.

3. The glucose-to-fructose ratio — why it matters

The small intestine absorbs glucose and fructose through two different transport channels (SGLT1 and GLUT5). Getting the ratio right lets you increase total carb absorption per hour without overwhelming the gut:

• Up to 60 g/hour: glucose alone is enough (1:0 ratio) because the SGLT1 channel is not yet saturated.
• 60–90 g/hour: aim for a glucose-to-fructose ratio of about 2:1.
• 90–120 g/hour: roughly 1:0.8 to 1:1, increasing the fructose share.
• Above 120 g/hour (elite athletes): near 1:1 to make the most of both transport channels.

4. Gut training over 6–10 weeks

The ability to tolerate carbs during exercise is a trainable skill, much like muscular endurance. A reference protocol:

• Week 1: start at 30 g/hour, with 1–2 training sessions per week that include carb intake.
• Weeks 2–7: add roughly 10 g/hour each week.
• Weeks 6–7: target tolerance of 80–90 g/hour.
• From week 8: progress toward your race-day target, up to 120 g/hour for professionals.

Key rules: always practice with the exact products you will use on race day, drink 150–200 ml of water per 30 g of carbs, and if digestive symptoms appear, hold at the current level for an extra week before increasing again.

5. Post-race carbohydrate recovery

• If your next session or race is within 8 hours: take 1.0–1.2 g of carbs per kg per hour for the first 4 hours, starting within 30 minutes of finishing.
• Adding 20–40 g of protein supports muscle synthesis, though it does not speed up glycogen resynthesis.
• Daily carb targets by training load: 3–5 g/kg (low intensity), 5–7 g/kg (moderate, ~1 hour/day), 6–10 g/kg (endurance, 1–3 hours of hard training), 8–12 g/kg (extreme, 4–5+ hours of hard training).

Important note

This is a general scientific summary, not a substitute for individualized nutrition advice. Athletes with underlying conditions (such as diabetes or digestive disorders) should speak with a physician or sports dietitian before applying any carb loading protocol, especially at intakes above 90 g/hour.

Source: IAMCOACH.ai — The Modern Carbohydrate Playbook: How to Fuel Endurance in 2026