Key takeaways
- For endurance efforts over 90 minutes, fuel intake during the session matters meaningfully. 30–60 g of carbs per hour is the default for moderate efforts.
- For efforts over 2 hours, multiple-source carbs (glucose + fructose) absorb faster than single-source. Most modern sports nutrition uses this principle.
- Carb-loading for events lasting 90+ minutes works — but the protocol is simpler than once thought. 8–10 g/kg of carbs per day for 1–3 days before is sufficient.
- Hydration with sodium matters more than carbs for sessions in heat or for heavy sweaters.
- Trial your fueling in training, not on race day. The single biggest mistake amateur endurance athletes make.
If you’ve started running, cycling, or hiking long enough that you’re using the words “long run” or “century ride,” your nutrition needs have shifted. Endurance training has different fueling demands than the gym session it might be replacing.
This article is the practical guide to endurance fueling. Carbs during effort, real-food vs. gels, pre-event eating, and the simple mistake-avoidance rules that turn most amateur endurance nutrition problems into solved problems.
It’s a deeper dive on §3 of Nutrition for Active Lives.
What endurance training demands#
Endurance efforts (over 60–90 minutes at moderate-to-high intensity) deplete muscle glycogen — your stored fuel. The longer or harder the effort, the more glycogen depletion, and the more fueling matters.
Three things shift compared to shorter training:
- Carbs become primary — glycogen depletion at 90+ minutes means refueling during the session matters
- Sodium losses accumulate — heavy sweating over hours produces meaningful electrolyte deficits
- Total daily calorie needs spike — endurance athletes often need 3,000–5,000+ calories on big training days
Each of these has practical implications.
Carbs during exercise#
The general rule:
| Effort length | Carbs per hour |
|---|---|
| Under 60 minutes | 0 (water only) |
| 60–90 minutes | 0–30 g (optional) |
| 90–150 minutes | 30–60 g |
| 150 minutes – 2.5 hours | 60–90 g |
| Over 2.5 hours | 60–120 g, possibly higher with practice |
For a 70 kg recreational runner doing a 2-hour long run: 60–90 g of carbs total during the run, taken in 30 g doses every 30 minutes (or smaller doses every 15).
Sources#
Anything that delivers carbs during exercise without GI distress:
- Sports drinks (15–25 g carbs per 8 oz)
- Energy gels (20–25 g per gel)
- Energy chews (3–6 g each, eat several)
- Real food: bananas (25 g), dates (15 g each), pretzels (5 g per pretzel), small candy bars
- Long-distance only: sandwiches, rice cakes, even mashed potatoes for ultra-endurance contexts
Multiple-source carbs#
For efforts over 2 hours, mixed-source carbs (glucose + fructose, typically in a 2:1 or 1:0.8 ratio) absorb faster than single-source glucose. The mechanism: glucose and fructose use different intestinal transporters; combining them increases total carbohydrate uptake.
Most modern sports drinks and gels use this principle. If you’re training for events over 2 hours, look for products labeled “glucose + fructose” or “multiple sources.”
Hydration during endurance#
The hydration discussion gets its own article — see Hydration for Athletes — but the endurance-specific points:
- Aim for 500–750 ml/hour unless your sweat rate testing shows otherwise
- Sodium 500–1,000 mg/hour for sessions over 90 minutes, especially in heat
- Heavy sweaters lose 1.5–2 g sodium per hour and need more
- Don’t over-hydrate with plain water during prolonged exercise — hyponatremia is a real risk in marathon and ultra contexts
Carb-loading for events#
For events lasting 90+ minutes, carb-loading can produce performance improvements by maximizing pre-event glycogen stores.
The modern protocol is simpler than the 1970s “depletion + load”:
- 1–3 days before the event, eat 8–10 g of carbs per kg of body weight per day
- For a 70 kg adult: 560–700 g of carbs/day during the load
- Maintain normal protein and reduce fat to make room for carbs
- The day before: carbs come from easy-to-digest sources; reduce fiber to avoid GI issues
- Don’t try novel foods during the load — stick to known ingredients
For events under 90 minutes (5K, 10K, sprint triathlons), full carb-loading isn’t necessary. A normal high-carb day before is sufficient.
The morning of an event#
A reasonable pre-event meal pattern:
3–4 hours before: the main meal. Carbs + small protein + minimal fat and fiber. Examples: oatmeal + banana + small amount of nut butter, or pancakes + maple syrup + scrambled eggs, or a sandwich on white bread.
1–2 hours before: lighter top-off. Toast with honey, banana, sports drink, energy bar.
15–30 minutes before: small simple-carb only. Date, half a banana, a few sips of sports drink.
The rule: the closer to start time, the simpler and lower-fiber the food. Fat and fiber slow gastric emptying.
Real-food vs. gels#
The “use only gels” school of thought is overstated. Real-food options work for many endurance contexts:
Where gels win:
- Compact, easy to carry
- Predictable carb dose per package
- Don’t require chewing
- Best for road racing
Where real food wins:
- Trail running, ultra distances, long bike rides where you have time to chew
- More palatable over many hours
- Can include protein and fat for ultra contexts where pure carbs get nauseating
A typical compromise for a 4-hour ride: gels and sports drink for the first 2 hours, then real food (sandwiches, rice cakes, crackers) when the GI system can handle it.
What to avoid#
A few specific patterns that derail endurance nutrition:
Trying new fuels on race day#
The #1 amateur endurance mistake. The brand of gel you’ve never used, the energy bar your friend recommended, the chia drink that sounds healthy. Race day is for known foods only.
Under-hydrating early#
Starting an endurance event already mildly dehydrated is hard to recover from once the effort starts. Drink consistently in the 4 hours before, then drink to schedule once underway.
Over-fueling early#
Eating too much carb in the first 30 minutes can cause GI distress during the harder middle portion of the effort. Start the fueling slow; build over time.
Forgetting electrolytes#
Long efforts in heat without sodium intake can produce cramping, hyponatremia, and DNFs. Include electrolyte-containing fluids or solid sources (salted pretzels, pickle juice) for any effort over 90 minutes in heat.
Trying to “save calories” during training#
Some weight-conscious endurance athletes under-fuel during long sessions to “save” calories. The result is poor recovery, slower sessions, and ultimately worse adaptations. Fuel the work; lose the weight in the kitchen, not in the run.
A reasonable race-week pattern#
For a half-marathon or 50-mile bike ride on Sunday:
- Mon-Thu: normal eating, normal training
- Fri (2 days out): start carb load — increase carbs to 7–8 g/kg/day, normal protein
- Sat (1 day out): continue carb load — 8–10 g/kg/day; reduce fiber and fat in the afternoon and evening; hydrate well; salt food slightly more than usual
- Sat dinner: familiar pasta-based meal with modest protein, low fat
- Sun morning (race day): main meal 3 hours before start; light top-up 1 hour before; gel 15 minutes before; coffee if usual
- During race: 30–60 g carbs/hour from gels + sports drinks; 500–750 ml/hour fluid; 500 mg sodium/hour
- Post race: carbs + protein + fluids within 1–2 hours
Frequently asked questions#
How many carbs do I need for a marathon?
A typical recreational marathoner: 60–90 g carbs per hour during the race, roughly 240–360 g total carbs over 4 hours, plus the carb load in the days before. Trained ultra-endurance athletes can take in 90–120+ g/hour with practice.
Should I eat protein during long runs or rides?
For sessions over 4 hours, modest protein (5–10 g/hour) supports recovery and can reduce muscle damage. For shorter endurance sessions, carbs alone are fine; recovery protein comes after the session.
Do I need to carb-load for a 5K?
No. A 5K is over too quickly to deplete glycogen meaningfully. A normal carb-rich meal the night before is plenty. Carb-loading is for efforts over 90 minutes.
What if gels make me feel sick?
Try real-food alternatives: dates, banana pieces, fruit leathers, honey packets, even rice cakes for longer events. Some athletes do better with chewable carbs (chews, jelly beans) than concentrated gels. Practice in training to find what works.
How do I fuel for a hike?
Hiking is more like ultra-endurance than typical training because the duration is long but intensity moderate. Pack 30–50 g carbs per hour from real food (trail mix, sandwiches, fruit, energy bars), plus electrolytes for sweat-heavy or hot conditions. The relaxed pace lets you handle real food well.
Where to go next#
- Nutrition for Active Lives — broader framework
- Hydration for Athletes
- Race-Day Nutrition: A 24-Hour Pre-Event Plan
- Pre-Workout Fuel
- Carbohydrates Decoded
Sources#
- Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. Carbohydrates for training and competition. Journal of Sports Sciences, 2011. PubMed
- Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement: Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise, 2016. PubMed
- Jeukendrup AE. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 2014. PubMed
- Bussau VA, Fairchild TJ, Rao A, Steele PD, Fournier PA. Carbohydrate loading in human muscle: an improved 1 day protocol. European Journal of Applied Physiology, 2002. PubMed
- Stellingwerff T, Cox GR. Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations. Applied Physiology, Nutrition, and Metabolism, 2014. PubMed