How to Fuel Long Runs During Marathon Training

A useful marathon long run should do more than prove you can survive on fumes.

Yes, the run builds fitness. Obviously. But it also teaches you whether your race-day nutrition plan is real or just something you typed into your notes app with way too much confidence.

That second job gets skipped all the time. People run 18 miles with one sad gel in their pocket, call it mental toughness, then try to eat six gels on race day like their stomach has been attending night school.

Buddy, no.

If you want to fuel a marathon well, long runs are where the plan becomes boring, automatic, and hard to mess up. The gel is not the plan. The grams are the plan, the timing is the plan, and the practice is the part that keeps it from becoming race-day fan fiction.

Your long run is not just fitness practice

Marathon fueling is a bad thing to discover at mile 19.

The broad sports nutrition guidance is pretty consistent: during endurance exercise, carbohydrate helps preserve performance, and longer events usually need more of it. The Academy of Nutrition and Dietetics, Dietitians of Canada, and ACSM position stand points runners toward carbohydrate before and during long efforts, with intake rising as duration and intensity rise (Thomas, Erdman, and Burke).

That is the science side. The practical side is uglier: your gut has to tolerate the product, the timing, the fluid, the pace, the weather, and the bouncing. If you only practice your marathon fueling on one big 20-miler, you are basically giving your stomach one rehearsal before opening night.

Good luck with that production.

The gut training guide goes deeper on the adaptation piece, but the short version is simple: eating while running is a skill. You get better at it by doing it, not by reading about it while your gels sit unopened in a drawer.

When should you start fueling a long run?

For most marathoners, the line is somewhere around 75-90 minutes.

If the run is shorter than that, you can usually finish fine without taking carbs during the run, especially if you ate normally beforehand. That does not mean fueling is useless, though. A short workout can still be a good place to test a gel, practice carrying fluids, or make race-day timing feel automatic.

Over 90 minutes, I think fueling should become normal, not dramatic, not a special event, just part of the run, like tying your shoes or trying to remember where you parked.

Here is my boring-but-useful default:

Run length	Fueling goal
Under 75 minutes	Usually optional, unless practicing a product or starting low on food
75-90 minutes	Practice one gel or small carb dose if this run supports race prep
90 minutes to 2 hours	Start fueling early and aim for 30-45 g/hr
2+ hours	Treat it like marathon practice and build toward your race target
Peak long runs	Use the exact products, timing, fluids, and caffeine you plan to race with

The first dose should come early. For marathon-specific long runs, that usually means around 25-35 minutes, then every 25-35 minutes after that depending on the gel size and your carb target.

What works badly? Waiting until you feel weak.

By then, you are already playing catch-up, and late-run you is not exactly the CFO of the operation. Early fueling keeps the whole thing calmer, which is boring in exactly the right way.

How many carbs per hour should you use?

Start with grams per hour, not gel count. This is where runners get sideways because gel count feels concrete and grams per hour sounds like homework.

Most standard gels are around 20-30 g of carbohydrate. Some drink mixes deliver 40-90 g per bottle. Chews can be anything from a few grams per piece to a full gel's worth if you eat the whole sleeve. Product math gets weird fast.

I would use this as the long-run target:

Runner / training stage	Long-run carb target
New to fueling while running	30-45 g/hr
Most marathoners	40-60 g/hr
Experienced and gut-trained	60-80 g/hr
Advanced, using glucose-fructose products	80+ g/hr, only if practiced

The higher numbers are not magic. They usually require practice and mixed-carb products, often some glucose plus fructose. Jeukendrup's carbohydrate recommendations helped move endurance advice past the old single-source 60 g/hr ceiling, but the key phrase is still "when tolerated" (Jeukendrup).

And that's where runners get into denial and error.

They see a pro taking 90 g/hr, buy Maurten or SiS Beta Fuel, and try it once during a peak long run. Maybe it works. Maybe it turns the final six miles into a public restroom scouting mission. The glucose-to-fructose guide explains why mixed carbs help, but the ratio does not fix bad pacing, dehydration, or zero practice.

For a first marathon, I would rather see someone hit 45 g/hr cleanly than write down 75 g/hr and spend race day negotiating with their lower intestine.

Want your long-run fueling matched to your marathon pace, body size, and weather? Build a personalized carb, fluid, and sodium plan in about 60 seconds with the free EnduranceOS planner.

Build it across the training block

You don't need to nail your final marathon plan in week one.

Actually, you probably should not. Early in a training block, the goal is just to make fueling feel normal. Later, you tighten the screws.

Early on, use long runs to test basic logistics. Can you open the gel without stopping? Does GU sit better than Maurten? Do chews annoy you because you hate chewing at tempo effort? Does drink mix work until the bottle starts tasting like warm syrup?

On long runs over 90 minutes, start around 30-40 g/hr. If that is one gel every 35-45 minutes, fine. The goal is consistency, not hero math.

This is also when breakfast starts to matter. The pre-race breakfast guide covers the morning part, but long runs are where you learn whether that bagel, banana, oatmeal, coffee, or sports drink actually behaves once you start running.

By the middle of the block, the plan should get less casual. If you want to race at 50-60 g/hr, practice that on several long runs and workouts. Not once. Several times. Practice on tired legs, in wind, in warmer weather, and on routes where you have to carry your own stuff.

This is where I would get specific:

• Take the first gel at 25-35 minutes.
• Repeat every 25-35 minutes.
• Take gels with water, not a big mouthful of sports drink.
• Count sports drink carbs if you use them.
• Log what worked, what tasted awful, and what made your stomach weird.

Tiny notes help. "GU salted caramel at 35/70/105, water each time, no slosh" is useful. "Fueled good" is vibes with a timestamp.

Peak long runs should answer boring questions before race day asks them rudely.

How many gels fit in your shorts? Which pockets bounce? Can you drink from a paper cup without wearing half of it? Does your caffeine gel belong at mile 16, mile 20, or nowhere because it makes your heart feel like it has a side hustle?

Use at least one major long run as a dress rehearsal: same breakfast, same shoes if practical, same fuel timing, same sports drink if the race publishes what will be on course, and the same caffeine plan if you use caffeine.

Not every long run needs to be a full race simulation, because that gets exhausting and weird. But if your exact fueling plan only exists in theory, it isn't ready yet.

Race week is not a product fair.

If somebody gives you a new gel at the expo, smile, take it home, and let it live in the cabinet until a training run. Same with drink mixes, bars, chews, sodium capsules, and mystery gummies from the bottom of the packet drawer.

The taper is for repeating what already works. You can adjust quantities, but the main cast should be set.

What should you actually eat or drink?

My boring answer for most marathoners is still gels plus water, and I know that sounds suspiciously simple for a sport that can turn socks into a 14-comment forum debate.

Gels are easy to count, easy to carry, and easy to time. If one gel has 25 g of carbs and your target is 50 g/hr, the plan is not rocket surgery: one gel every 30 minutes. The marathon gel timing guide has full sample schedules by finish time if you want the race-day version.

Drink mix can work too, especially if you hate gels or you are trying to reach higher carb targets. Tailwind, Gatorade Endurance, Maurten Drink Mix, and SiS Beta Fuel can all fit a plan. But drink mix ties your carbs to your fluid intake, and that can get messy when the weather changes.

Chews are fine if you like smaller bites. Some runners tolerate them better because they can nibble instead of taking a whole gel at once. Others hate chewing while breathing hard, which is not a character flaw. It is useful information.

A gel plus sports drink plus a concentrated bottle can dump a lot of carbohydrate into your gut quickly. That might be fine on the bike. Running is harsher. If you are taking a gel, chase it with water when you can. If you are using sports drink for carbs, count those grams so you do not accidentally turn mile 15 into sugar lasagna.

The gels vs. chews vs. drink mix guide goes deeper on format choice. For long-run practice, pick one main format and one backup. Simple beats clever here.

Hydration and sodium are part of the rehearsal

Long-run fueling is not only carbs, even though carbs are the loudest part of the conversation.

Fluid and sodium matter because they change how your stomach handles the fuel. Run a hard two hours in cool weather and you might drink very little. Run the same two hours in July and suddenly every gel feels like spackle unless you have enough fluid coming in.

This is where sweat-rate testing helps. A simple before-and-after weigh-in can tell you whether you lose 0.5 L/hr, 1.0 L/hr, or way more. The sweat rate article covers the math, and the hot weather nutrition guide explains why your cool-weather plan is only a starting point.

Sodium is similar. You probably don't need to copy some stranger's 1,000 mg/hr rule, but you do need to know whether you are a salty sweater, whether your drink mix already contains sodium, and whether the marathon is likely to be warm. The sodium guide is the better place for that full rabbit hole.

For long runs, keep it practical: practice drinking while running, learn what your stomach tolerates with gels, use sodium when the run is long, hot, or sweaty enough to justify it, and don't drink plain water endlessly just because you are nervous.

That last point matters. Overdrinking is real, especially for slower runners who are out there longer and pass more water stops. The hyponatremia article covers the safety side in more detail.

The underfueling trap

Some runners turn every long run into a fasting experiment.

I get the appeal. It feels tough. It feels clean. It feels like you are teaching your body to run on fumes, which sounds cool until race day shows up and you need to run 26.2 miles at goal pace while eating enough carbohydrate to keep the wheels on.

There is a place for easy runs without fuel, and there is a place for low-intensity training where you are not trying to mimic race demands. But if most of your marathon-specific long runs are underfueled, you are practicing a different event than the one you plan to race.

Smaller athletes and female athletes get especially bad advice here. A 55 kg runner and an 85 kg runner do not have the same glycogen storage, sweat rate, or margin for accidentally under-eating, and "just run it fasted" can turn into a bigger health and recovery problem when training volume climbs.

So yes, body size matters. Sex can matter too. But the lazy takeaway is "women need less fuel," and that is not what I would tell anybody. A smaller runner may need fewer total grams than a larger runner at the same relative effort, but they also may have less stored energy and less room for sloppy recovery. The better answer is to set a plan by duration, body size, tolerance, and race goal, then test it instead of copying some guy who treats black coffee like a meal plan.

Average is a trap.

The mistakes that make race day weird

Most marathon fueling problems start in training.

Not all of them, obviously. Heat happens. Bad pacing happens. Aid stations run out of the thing you expected because apparently the race had one job and chose chaos. Still, a lot of disasters are built slowly over weeks.

The usual suspects:

Waiting too long to eat. If your long-run habit is "first gel when I feel tired," race day will punish that, so fuel before you need it.

Changing products every week.
Variety is nice for normal life. Race fueling needs repetition. Pick a main product and give your gut enough chances to recognize it.

Practicing only in perfect weather.
A plan that works at 48 F may feel gross at 72 F. If your marathon could be warm, test warm.

Ignoring sports drink carbs.
If the course drink has carbs, count them. If you take a gel with sports drink because the water table was crowded, count that too.

Treating caffeine like free speed.
Caffeine can help, but it is still a dose. If caffeine gels sit badly or make you jittery, find out on a long run, not under the mile 20 timing mat. The caffeine timing guide covers the mg/kg side.

Never writing anything down.
You don't need a spreadsheet cult, but write enough that future you can repeat the good runs and avoid the dumb ones.

A simple long-run fueling progression

Here is what this might look like for a runner building toward a marathon.

Training phase	Example long-run fueling
10-12 weeks out	One gel around 35 minutes on a 90-minute run
8-10 weeks out	30-45 g/hr on long runs over 90 minutes
6-8 weeks out	45-60 g/hr with the same gel or drink mix you may race with
4-6 weeks out	Full race timing on a key long run, including fluid and sodium
2-3 weeks out	Final dress rehearsal, then no new products
Race week	Repeat the plan, do not get cute

Let's make that less fake.

Say you are targeting a four-hour marathon and want around 50 g/hr. In training, that might become one 25 g gel at 30, 60, 90, and 120 minutes on a long run, with water each time. If the run is hot, you also practice carrying fluid or planning a loop with refills. If the race has Gatorade Endurance on course and you plan to use it, you test that too.

That is not exciting, which is perfect. Exciting nutrition plans usually become exciting for the wrong reasons.

Turn your long-run notes into race-day numbers

By the end of marathon training, you should know a few things.

You should know your breakfast, your first gel time, your usual grams per hour, your fluid rhythm, whether caffeine helps, and what product your stomach accepts when the pace gets real. You should also know your backup plan for dropped gels, crowded aid stations, hot weather, and the moment when your brain departments stop taking meeting notes.

That is the point of long-run fueling: evidence, not perfection.

Quick science note: this article is general endurance nutrition guidance, not medical advice. If you have diabetes, a history of eating disorders, GI disease, hyponatremia risk, or any condition that changes how you handle carbs, fluids, or sodium, work with a qualified clinician or sports dietitian.

For everyone else, start simple: fuel long runs over 90 minutes, practice the first gel early, build toward your race target, and stop treating race-day nutrition like something you can cram for.

The EnduranceOS planner turns your marathon details into a personalized carb, fluid, and sodium plan based on your race, your body, and your conditions. It takes about 60 seconds, and it is free.