You’re 14 miles into an 18-mile long run during marathon training.
Your legs feel heavy.
Your pace has dropped 2 minutes per mile.
Your mind keeps searching for an excuse to stop early.
You bonked. You hit the wall because you didn’t fuel properly.
This doesn’t have to happen on your next long run.
Proper fueling keeps your energy stable, your pace consistent, and your training productive.
So, in this article you’re going to learn the research-backed practical advice on fueling for long training runs.
- Understand your body’s fuel system and when glycogen depletion happens
- Know exactly what to eat before a long run and when to eat it
- Learn when to start fueling during your run and how much carbs your body can use
- Discover the best hydration strategy for runs over 90 minutes
- Get a practical recovery nutrition plan to maximize your next training session
How Much Glycogen Does Your Body Burn on a Long Run?
Glycogen is your primary fuel source for running.
Your muscles store glycogen as glucose chains, and they pull from these stores continuously as you run.
Under 90 minutes, you have enough glycogen to fuel the effort without external carbohydrate intake.
Research has shown that approximately 90 minutes of running depletes 50% of your resting glycogen stores.
Once you cross the 90-minute threshold, glycogen depletion accelerates.
Your muscles’ ability to contract with force declines.
Your central nervous system struggles to maintain pace.
This is bonking. With the right fueling strategy, it’s entirely preventable.
Your liver also stores glycogen, and it releases glucose into your bloodstream to top up muscle fuel.
During long runs, liver glycogen depletes too.
After 2 to 2.5 hours, both your muscle and liver glycogen stores are critically low.
This is why fueling during runs over 90 minutes is non-negotiable.
To maintain performance and finish strong, you need to match your fuel intake to your body’s glycogen burn rate.
What Should You Eat Before a Long Training Run?
Your pre-run meal sets the glycogen stage for the entire run.
Eating the right carbohydrates at the right time ensures your muscle and liver glycogen stores are topped off before you start.
Research has shown that consuming 1 to 4 grams of carbs per kilogram of body weight, 1 to 4 hours before running, improves endurance performance and delays fatigue.
The timing window is wide because your digestive system needs time to break down food and absorb glucose.
If you eat too close to your run start (within 30 minutes), you’ll experience stomach discomfort, nausea, and cramping.
If you eat 4 or more hours before, your glycogen stores may start to decline again before you begin.
Aim for 2 to 3 hours pre-run, which gives your stomach time to settle and your bloodstream time to absorb the fuel.
A pre-run meal should be carbohydrate-rich, low in fiber, and low in fat and protein.
Your body digests these quickly without causing GI distress.
Examples: a bagel with honey, oatmeal with banana, toast with jam, rice with chicken, or cereal with milk.
For a 150-pound (68 kg) runner, aim for 1.5 to 2.5 grams of carbs per kg.
That’s roughly 100 to 170 grams of carbs before your long run.
Think 1 to 2 cups of cooked rice, a large bagel plus banana, or 2 slices of toast with jam plus a glass of juice.
A proper pre-run meal fuels the first 60 to 90 minutes of your run.
After that, your glycogen stores begin depleting faster than your pre-run meal can support.
This is when in-run fueling becomes essential.
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When Should You Start Fueling During a Long Run?
The biggest fueling mistake runners make is waiting too long before they start eating on a run.
Runners who believe they can push through the first hour or two without fuel are asking their bodies to burn stored glycogen until it’s nearly gone.
By the time you feel energy drop, your glycogen stores are already critically depleted.
Your performance crashes before your stomach has a chance to absorb the fuel you just ate.
Research indicates that starting carbohydrate intake by 45 to 60 minutes into exercise, before glycogen depletion becomes severe, delays fatigue onset and maintains running economy.
If you wait until you feel tired, you’ve waited too long.
Fatigue is a symptom of glycogen depletion that has already happened.
Start fueling at 45 to 60 minutes into your long run.
Your glycogen stores still have reserve capacity, and your digestive system is primed to absorb fuel steadily throughout the remainder of your run.
Runners who start early maintain their effort and pace throughout.
Runners who wait hit the wall because they’re asking their depleted muscles to absorb fuel they desperately need all at once.
Once you know when to start, the next question is how much to take in per hour.
How Many Carbs Do You Need Per Hour on a Long Run?
Your body has a ceiling for how many carbohydrates it can oxidize (burn) per hour.
This ceiling is set by your intestinal absorption capacity and your muscles’ glucose transporter availability.
Research has shown that consuming 60 grams of carbohydrates per hour maximizes carbohydrate oxidation during long-duration running and delays glycogen depletion.
The sweet spot for most runners is 30 to 60 grams of carbs per hour.
At this intake level, your intestines absorb glucose efficiently, your muscles use the fuel immediately, and your stomach stays comfortable.
If you consume fewer than 30 grams per hour, your muscles burn glycogen faster than you’re replenishing it.
If you consume more than 60 to 90 grams per hour, your intestines can’t absorb the fuel fast enough.
The carbs sit in your stomach, causing bloating, cramping, and nausea.
One gel provides roughly 25 to 30 grams of carbs.
One bottle of sports drink (16 to 20 oz) provides 14 to 20 grams of carbs.
A banana provides 27 grams.
An energy bar provides 40 to 50 grams.
A practical formula: 1 gel (30g) plus 1 bottle of sports drink (16 to 20g) taken every 60 minutes equals 46 to 50 grams per hour.
Alternatively, take 2 gels per hour, or 1 gel plus real food (banana or bar) plus water.
During runs longer than 2.5 hours, vary your fuel sources.
Gels are convenient, but relying solely on gels can cause taste fatigue and GI distress.
Mix in a banana, energy bar, or real food like pretzels or crackers.
Hitting your carb target per hour keeps your muscles’ fuel engine running at full capacity, maintaining your pace and effort from mile 5 all the way to the finish.
For how to turn this into a personalized fueling strategy based on your pace, see how elite runners build their refueling approach and apply those same principles to your training.
What’s the Best Way to Hydrate on a Long Run?
Dehydration amplifies glycogen depletion.
When you’re low on fluids, your body’s ability to absorb glucose declines, your core temperature rises, and your cardiovascular system works harder.
Even correct fueling can’t fully offset poor hydration.
Research indicates that drinking 400 to 800 milliliters of fluid per hour, adjusted for body size and sweat rate, maintains optimal hydration and performance during long runs.
Your sweat rate varies based on fitness level, body size, genetics, running pace, temperature, and humidity.
A 150-pound runner might sweat 1 to 1.5 liters per hour.
A 200-pound runner might sweat 1.5 to 2 liters per hour.
The general target is 400 to 800 milliliters (14 to 27 ounces) per hour.
That replaces 50 to 75% of your sweat loss. Your body is designed to tolerate some fluid deficit during exercise, but staying below 2% body weight loss is the performance threshold.
Plain water alone is insufficient for runs over 90 minutes.
Sodium helps your body retain fluid and maintain blood sodium concentration.
Without sodium, your body excretes the water you drink without fully absorbing it.
Most sports drinks contain 300 to 600 milligrams of sodium per 16-ounce bottle.
Aim for 500 to 700 milligrams of sodium per hour to match your typical fluid intake.
If you’re drinking only water, eat a salty snack (pretzels, salt tablet) to maintain sodium levels.
Test your sweat rate and hydration strategy during training runs.
Weigh yourself before and after a 1-hour run (naked, post-bathroom). Each pound lost equals roughly 16 ounces of sweat.
Proper hydration supports carbohydrate absorption, maintains cardiovascular stability, and prevents heat-related fatigue.
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If you are unsure about how to calculate how much water to consume, and electrolytes to use, this will give you your exact needs.
What Should You Eat After a Long Run?
Recovery starts the moment you stop running.
Your muscles are primed to absorb glucose and amino acids.
This window, the first 30 to 60 minutes post-run, is your most powerful time to refuel and recover.
Research has shown that consuming carbohydrates and protein within 30 to 60 minutes post-exercise maximizes glycogen resynthesis and muscle protein repair.
Your muscles’ glucose transporter activity is highest immediately post-run.
Glycogen synthase, the enzyme that rebuilds glycogen, is also maximally active in this window.
Every gram of carbs you consume here is absorbed and stored more efficiently than carbs consumed hours later.
Your target is 1.2 grams of carbs per kilogram of body weight, plus 0.3 to 0.4 grams of protein per kilogram.
For a 150-pound (68 kg) runner, that’s roughly 80 grams of carbs and 20 to 27 grams of protein.
Practical recovery meals include chocolate milk (carbs plus protein, easy to drink post-run), a banana with 2 tablespoons of peanut butter, a bowl of rice with grilled chicken, pasta with lean ground turkey, toast with egg, or a smoothie with fruit, yogurt, and granola.
If you’re not hungry immediately after a run, consume liquid carbs and protein.
A large sports drink plus a protein bar covers the window.
Wait no more than 60 minutes before your full recovery meal.
Quick recovery nutrition sets you up for the next training session by reducing muscle soreness and accelerating glycogen repletion.
Long Run Fueling by Distance: Your Reference Guide
| Distance | Pre-Run Fueling | During-Run Carbs/Hour | Post-Run Recovery (within 60 min) |
| 8 to 10 miles (13 to 16 km) | 100 to 150g carbs, 2 to 3 hours before | Not needed (under 90 min) | Light: fruit plus toast, or small smoothie |
| 10 to 14 miles (16 to 22 km) | 120 to 170g carbs, 2 to 3 hours before | 30 to 40g per hour (start at 45 to 60 min) | 80g carbs plus 20g protein (rice plus chicken, pasta plus lean protein) |
| 14 to 18 miles (22 to 29 km) | 140 to 200g carbs, 2 to 3 hours before | 45 to 60g per hour (start at 45 min) | 100g carbs plus 25g protein (large bowl pasta plus meat, smoothie plus granola) |
| 18+ miles (29+ km) | 160 to 220g carbs, 2 to 3 hours before | 60g per hour, mixed sources (gels plus drink plus solid food) | 120g carbs plus 30g protein (full meal: rice plus protein plus veggies) |
Use this table as your fueling checklist.
Adjust the carb amounts based on your body weight and personal tolerance.
A 120-pound runner might stay on the lower end of each range. A 200-pound runner moves toward the higher end.
The principles stay the same: fuel early, fuel frequently, hydrate alongside fuel, and recover quickly.
Your long runs are where you build both aerobic fitness and metabolic resilience. Proper fueling ensures every mile teaches your body to run strong.
