Race Fueling From 800m to Marathon: The Working Numbers

Most runners do not learn race fueling from a spreadsheet. They learn it the hard way: training is solid, but one gel is not enough and the bonk starts creeping in during the final 5K; the day is hotter than expected and the half marathon suddenly needs more sodium; or a new gel turns the stomach sour and steals attention from running well.

The rule is simple: short races protect comfort and speed; long races protect carbohydrate availability, blood volume, sodium, and a gut that has already practiced the plan. The intermediate step is where the numbers become useful without becoming a spreadsheet religion.

This guide is for healthy adult runners who are ready to plan more deliberately. It is still a rough guide, not individualized nutrition, medical, or performance advice. Your needs can change with sex, body size, training status, heat, sweat rate, medications, GI history, and race duration.

The examples below use a 70 kg runner because it makes the math concrete. Scale the g/kg and ml/kg ranges to your own body mass, then test the plan in training before racing it.

Before you mix your own brew

At-home solutions can work well for intermediate runners. Maltodextrin, sugar or fructose, sodium, and flavoring can create a cheaper bottle than race gels. But the standard is not whether the mix looks smart on paper. The standard is whether you can make it the same way twice, carry it comfortably, drink it at race pace, and tolerate it when your gut has less blood flow than it wants.

If the homemade version adds too much friction, use the boring commercial option. If the commercial option is too expensive to practice, simplify the homemade version until it is repeatable. A fueling plan that never gets rehearsed is not a plan.

Race fueling matrix for an average runner

Use this table as a duration filter, not a commandment. If the race is short, protect a light stomach and fast legs. If the race is long, protect the supply line: carbohydrate, fluid, sodium, and a gut that has rehearsed the work.

Race	T-48h to T-24h carbs	Race morning	During race	Hydration/sodium
800m	3-6 g/kg/day. For 70 kg: 210-420 g/day.	1-2 g/kg carbs 3-4h out if needed. Keep volume small.	0 g. Optional mouth rinse only.	5-7 ml/kg 4h out. For 70 kg: 350-490 ml.
1500m / mile	5-7 g/kg/day. For 70 kg: 350-490 g/day.	1-2 g/kg 2-4h out. Toast, bagel, oats, rice, banana.	0 g. Tiny 10-15 g pre-start carb only if practiced.	Normal electrolytes. Avoid hyperhydration.
3K / 5K	5-8 g/kg/day. For 70 kg: 350-560 g/day.	1-2 g/kg 2-3h out. Low fat, low fiber.	0 g for most runners. Mouth rinse or 10-20 g in final 10 min if tested.	Start euhydrated. Add 300-600 mg sodium with morning fluids if hot or salty sweater.
10K	6-8 g/kg/day. For 70 kg: 420-560 g/day.	1-3 g/kg 2-4h out. For 70 kg: 70-210 g.	0-30 g/h. If slower than 60 min, consider 20-30 g/h.	Usually 0-400 ml/h unless hot. Do not gain weight from fluid.
Half marathon	7-10 g/kg/day for 24-48h. For 70 kg: 490-700 g/day.	2-4 g/kg 3-4h out. For 70 kg: 140-280 g.	30-60 g/h. Faster runners may need only one gel; slower runners need more time-based fuel.	400-800 ml/h as tolerated and conditions demand. Include sodium if sweating heavily.
Marathon	8-12 g/kg/day for 36-48h. For 70 kg: 560-840 g/day.	1-4 g/kg 3-4h out. For 70 kg: 70-280 g, low fiber and low fat.	45-60 g/h to start. Build to 60-90 g/h if gut-trained. Elite or heavily gut-trained upper work may reach 90-120 g/h, but that is not a cold race-day experiment.	Common range: 450-750 ml/h. Sodium often 500-1000 mg/L or enough to match sweat without overdrinking.

Protein, fat, and fiber: the digestion-speed layer

Nutrient	Useful range	Race-week use
Protein	Daily: 1.2-2.0 g/kg. For 70 kg: 84-140 g/day.	Keep the pre-race meal moderate. In the final 2h, avoid heavy protein. During marathon fueling, keep protein minimal unless using ultra-style food.
Fat	Often at least 20-25% of daily energy, or roughly 0.6-1.0 g/kg/day as a practical floor.	Do not cut fat chronically, but keep it low in the final pre-race meal because it slows digestion.
Fiber	Normal training intake is individual. Low-residue race taper often means about 10-15 g/day in the final 24h for sensitive runners.	For half marathon and marathon, reduce beans, bran, large salads, cruciferous vegetables, and whole grains 24-48h out if they bother your gut.

Practice is the real upgrade

The gut adapts to what it repeatedly sees. Practice does not have to mean taking gels on every run. It means choosing specific sessions where you rehearse the dose, concentration, timing, and product format you expect to race with. Long runs, marathon-pace work, and heat exposure are better tests than easy jogs around the block. That is the long-race side of the rule: the fuel only helps if the gut can keep delivering it.

Write down what happened. Note pace, heat, fluid volume, sodium, carbohydrate grams per hour, caffeine, urgency, nausea, stitch, bloating, and whether the plan was easy to execute. That symptom log is more useful than guessing after race day.

Why glucose-fructose matters after 60 g/hour

If you are taking less than about 60 g carbohydrate per hour, the exact carbohydrate blend matters less. Once you push above that, glucose-only fueling can saturate the main glucose transporter. Mixed transportable carbohydrate - usually glucose or maltodextrin plus fructose - uses more than one pathway and can raise total carbohydrate availability.

If you have heard runners talk about 100 g/hour plans, put that number in context. That level is not a personality test. It is a trained tolerance target for longer races, usually built gradually from 30 to 45 g/hour, then 45 to 60 g/hour, then higher only if the gut stays calm and the race actually needs it.

Caffeine numbers without the bravado

Start low. Many runners do well with 1-3 mg/kg caffeine 45-60 minutes before a race. A common evidence-based range is 3-6 mg/kg, but that can be too much for anxious, caffeine-sensitive, smaller, or GI-prone runners. For 70 kg, 1-3 mg/kg is 70-210 mg; 3-6 mg/kg is 210-420 mg. Marathoners using caffeinated gels should count the total across the whole race.

Race-day timing

• 3-4 hours before: the main carbohydrate meal.
• 60 minutes before: avoid a new large carb bolus if you are prone to rebound low blood sugar or stomach upset.
• Final 10 minutes: a small 10-20 g carbohydrate hit or mouth rinse can be useful because it is too close to the start to create the same pre-race digestion problem.
• Every 10-20 minutes in longer races: small repeat doses usually beat large emergency doses.

Safety check

Do not chase numbers blindly. No one wants to become the stumbling, confused runner who cannot stand steadily on their own feet. If you are nauseated, confused, vomiting, swelling, wheezing, faint, or unusually disoriented, stop and get medical support from a race marshal, aid station, or medical volunteer. Dehydration and hyponatremia can look similar from the outside, and the wrong fluid choice can make the problem worse. For long races, sodium belongs in the plan, but sodium does not make endless plain-water drinking safe. [7, 8]

Sources

1. Jeukendrup AE. Training the Gut for Athletes.
2. Fuchs CJ, Gonzalez JT, van Loon LJC. Fructose co-ingestion to increase carbohydrate availability in athletes.
3. Dominguez R, et al. Nutritional needs in the professional practice of swimming: a review.
4. Stellingwerff T, Bovim IM, Whitfield J. Contemporary Nutrition Interventions to Optimize Performance in Middle-Distance Runners.
5. Viribay A, et al. Effects of 120 g/h of Carbohydrates Intake during a Mountain Marathon.
6. Guest NS, et al. International society of sports nutrition position stand: caffeine and exercise performance.
7. Hew-Butler T, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference.
8. Athletics Canada Road. National Road Race Standards badges and event safety planning.