You can train perfectly for sixteen weeks and still wreck your marathon with bad fueling on race day. The marathon is unique among common race distances because it sits exactly at the limit of how long the body can sustain effort on stored carbohydrate. Liver and muscle glycogen together hold roughly 1,800-2,200 calories. A 70 kg runner burns 2,800-3,500 calories during a marathon, depending on pace. The math doesn’t add up without taking in calories during the race.

This guide covers what to eat the week before, the morning of, during the race, and immediately after — with the science of why each piece matters.

Definitions

Glycogen: the stored form of carbohydrate in your muscles and liver. The primary fuel for marathon-pace running.
Carb loading: a dietary protocol to maximize glycogen stores in the days before a race.
Gel: a packaged 25-30 g carbohydrate dose, typically a mix of maltodextrin and fructose, designed for during-race consumption.
Hyponatremia: dangerously low blood sodium, almost always caused by drinking too much plain water during exercise. More dangerous than mild dehydration.
Bonking / hitting the wall: the sudden severe fatigue caused by glycogen depletion, typically at km 30-35 of a marathon.

The week before: carb loading

Carb loading is not pasta the night before. It’s a 2-3 day protocol where you raise the percentage of total calories from carbohydrate to 65-75%, while keeping total calories roughly stable. Trained muscles can store 20-50% more glycogen than usual when this is done correctly.

Three days out

Cut back on fat and fiber. Increase carbohydrate. Target roughly 8-10 g of carbs per kg of body weight per day. For a 70 kg runner, that’s 560-700 g/day. Sources: rice, pasta, bread, potatoes, oatmeal, bananas, sports drinks, low-fiber breakfast cereals.

Two days out

Same carb intake. Reduce training volume to 30-50% of normal — short, easy runs only. Drink to thirst plus a little extra; aim for pale-yellow urine.

The day before

Eat your largest carb meal at lunch, not dinner. Pasta or rice with a small amount of lean protein, no heavy sauces, no novelty foods. Dinner is normal-sized: avoid the classic mistake of an enormous pre-race pasta dinner that disrupts sleep and digestion. Hydrate through the day; stop drinking heavily after dinner so you sleep without bathroom interruptions.

What to avoid in race week

Anything new. Race week is not the time to try a new gel, a new dinner, or a new restaurant.
High-fiber foods (beans, bran, large salads). They’re great in normal training; the day before a race they raise GI risk.
Excess fat. Slows gastric emptying.
Alcohol. Suppresses overnight glycogen synthesis.

Race morning

The pre-race meal restocks liver glycogen, which depletes overnight. Eat 2-4 hours before the start, in the range of 1.5-3 g of carbohydrate per kg body weight. For a 70 kg runner, that’s 105-210 g of carbs.

Reliable race-morning options:

Oatmeal with banana, honey, and a splash of milk.
Bagel with jam (skip the cream cheese unless you’ve trained on it).
White rice with a soft-boiled egg.
Two slices of toast with peanut butter and a banana.
Sports drink + plain energy bar if you can’t stomach solid food early.

Drink 400-600 ml of water or sports drink with the meal, then sip 200 ml roughly 30 minutes before the start. Avoid gulping water in the final hour — it just produces a bathroom break and dilutes blood sodium.

During the race: the fueling plan

Recommendations from sports nutrition research consistently land in the same range:

30-60 g carbs/hour for races under 2.5 hours.
60-90 g carbs/hour for races over 2.5 hours, especially when using glucose+fructose mixes that allow higher absorption rates.

One typical gel = 22-30 g carbs. So a sub-3:30 marathoner needs roughly 4-5 gels; a 4:00-4:30 marathoner needs 5-7 gels.

Practical fueling timeline (for a 4-hour goal)

0:00 (start): nothing. You ate breakfast.
0:30 (≈km 8): first gel + 200 ml water at next aid station.
1:00 (≈km 16): second gel + water.
1:30 (≈km 24): third gel.
2:00 (≈km 31): fourth gel.
2:30 (≈km 37): fifth gel — the “save your race” gel.
3:00-3:30: optional sixth gel if you’re tolerating fuel well; otherwise sip sports drink.

The single most common mistake is taking the first gel too late. By the time you feel hungry or weak, you’ve already lost 1-2 minutes that you can’t recover.

Choosing gels: glucose vs glucose+fructose

Pure-glucose gels (and most older formulations) cap carbohydrate absorption at roughly 60 g/hour because there’s only one transporter (SGLT1) carrying glucose across the gut wall. Mixed glucose+fructose gels (in roughly a 2:1 ratio) use a second transporter (GLUT5) and can deliver up to 90 g/hour of usable carbohydrate. For runners targeting >60 g/hour, mixed gels are meaningfully easier on the stomach and more effective.

Use our nutrition calculator to build a personalized schedule based on weight, pace, and finish time.

Hydration and sodium

Drink to thirst plus a small margin. Most runners need 400-800 ml/hour, but variance is huge — sweat rate ranges from 250 ml/hour (small runner, cool weather) to 2 L/hour (large runner, hot weather).

The bigger danger than mild dehydration is over-hydration. Hyponatremia — diluted blood sodium — has killed marathoners. The classic profile is a slower runner who drinks at every aid station “to be safe.” Symptoms: confusion, nausea, swollen hands. If your hands feel tight in your gloves at km 20, you’re over-hydrated, not under-hydrated.

Sodium intake during the race: roughly 300-700 mg/hour. Most sports drinks supply this; if you’re using only water and gels, consider salt tabs or sodium-rich electrolyte mixes, especially in hot weather.

After the race: the recovery window

The first 30-60 minutes after the finish is the highest-leverage nutrition window of the day. Glycogen synthesis runs at roughly 50% above normal in this window. Targets:

Carbs: 1.0-1.5 g/kg body weight in the first 30 minutes (70-100 g for a 70 kg runner).
Protein: 20-30 g, ideally with leucine-rich sources (whey, milk, eggs).
Fluids: ~150% of estimated fluid loss over the next 4-6 hours.
Sodium: a salty snack with the meal helps fluid retention.

Reliable recovery options: chocolate milk + banana; bagel with peanut butter + sports drink; rice bowl with chicken; smoothie with whey, milk, banana, and oats.

Within 2-3 hours, eat a normal full meal. Within 24 hours, your appetite often surges as muscle damage and inflammation peak; honor it.

Common nutrition mistakes

Trying a new gel on race day. Stomach distress at km 18 has cost more sub-4 attempts than any single training mistake.
Carb-loading total calories instead of percentage. Massively overeating raises GI risk; what matters is the carb proportion.
Drinking only water with double-sugar gels. Most modern gels expect water on board. Mixing gels with sports drink can deliver too much sugar at once and trigger GI upset.
Skipping breakfast on race morning. “I felt nervous, couldn’t eat” is a documented predictor of late-race blowups.
Over-hydrating in cool weather. The “drink at every station” reflex is a hyponatremia risk in 10 °C conditions.

What this means for your training

Treat fueling like a workout. Practice the exact race-day breakfast and the exact gel/drink schedule on at least three long runs in the final eight weeks. By race day, your stomach should be as well-trained as your legs. Use the weight impact calculator to understand how your body weight changes your energy needs.

FAQ

How many gels do I need for a marathon? Most runners need 5-7 gels: one every 25-35 minutes, starting at 30-40 minutes into the race. Faster runners need fewer (less time on course); slower runners often need more.

Should I carb-load if I’m running 4+ hours? Especially if you’re running 4+ hours. The longer you’re racing, the more glycogen storage matters. Three days of 8-10 g/kg/day is the standard protocol.

Can I run a marathon without gels? Some runners do, with carbohydrate from sports drinks, chews, or whole foods like bananas. The total carb intake target is the same; gels are just a convenient delivery format. “No-fuel” marathons almost always end with a much harder back half.

What about fasted training? Some easy and steady runs can be done fasted to enhance fat oxidation, but race day should never be fasted. Train fasted, race fueled.

How much should I drink during a marathon? Most runners need 400-800 ml/hour. Drink to thirst plus a small margin. Color of urine pre-race and weight change post-race are better feedback than rigid hourly volume.

What should I eat the night before? A normal-sized, familiar carb-rich meal (rice, pasta, potatoes) with a moderate amount of lean protein. Avoid heavy sauces, large salads, and anything you haven’t eaten before.

Why do I get GI distress with gels? Most often: too much carbohydrate too quickly, dehydration, or dehydrated gels without enough water. Try mixed glucose-fructose gels, take with 100-150 ml water, and practice in training.

Caffeine: the legal performance enhancer

Caffeine is among the best-studied legal aids for endurance. A dose of roughly 3-6 mg per kg body weight, taken 30-60 minutes before the start, has been shown across many studies to improve endurance performance by roughly 1-3%. For a 70 kg runner, that’s 210-420 mg — a strong cup of coffee plus a caffeinated gel.

Practical guidelines:

Test caffeine in long runs before relying on it for race day. Some runners get GI upset or jitters.
Don’t start the morning of a race with multiple energy drinks; you’ll spike too early.
Mid-race caffeine — typically in the third or fourth gel — is well-tolerated and useful for the back half.

Hydration: a sweat-rate test

Most runners underestimate or overestimate their fluid needs. A simple test:

Weigh yourself naked before a 60-minute run.
Run at marathon pace, drinking nothing.
Weigh yourself naked immediately after.
The difference in kg is roughly your sweat loss per hour. 1 kg lost ≈ 1 L of sweat.

Most runners will lose 0.5-1.5 kg per hour at marathon pace in moderate weather. Multiply by the time you’ll be out there for total fluid needs. In hot weather, sweat rate can double, but maximum gut absorption rates cap your useful intake at roughly 1 L/hour regardless.

Marathon Nutrition: What to Eat Before, During, and After.