Why fueling during the event matters

The body stores about 2,000-2,500 calories of muscle and liver glycogen. A marathon burns roughly 2,500-3,500 calories total for most runners. The math is unforgiving: without fueling during the race, you run out of glycogen before the finish.

This is the physiological basis of 'the wall' — the sudden drop in pace and energy that hits many marathoners around mile 18-22. It's not psychological. It's the body running out of carbohydrate substrate for the brain and working muscles.

Proper in-race fueling prevents most bonks. The protocol is well-researched, well-tested, and accessible to recreational athletes. It just requires practice.

The headline numbers come from work on carbohydrate oxidation during exercise: a single carbohydrate source is absorbed and burned at up to roughly 60g per hour, while blends of multiple transportable carbohydrates push that toward 90g per hour on longer events. That is why modern gels and drinks combine glucose with fructose instead of relying on one sugar. It is also why the gut needs training: the ceiling is absorption, not willpower.

The basic protocol

For most adult marathoners:

  • 30-60 grams of carbohydrate per hour during the race
  • Take in 200-400 mg of sodium per hour with the carbs
  • Drink 16-32 oz of fluid per hour (more in heat)
  • Start fueling early — within the first 30-45 minutes, not when you feel low

For well-trained athletes who have practiced:

  • Up to 90 grams per hour is achievable and improves performance
  • Requires using mixed-sugar fuel sources (glucose + fructose)
  • Requires gut training over weeks

The research on 90g/hour intake is increasingly strong for elite-trained athletes. For recreational marathoners, 30-60g/hour is more realistic and produces most of the benefit.

What to actually use

Energy gels

The standard race fuel. ~25g carbs per gel. Common brands: GU, Maurten, Honey Stinger, SiS, Spring Energy, Hammer Gel.

Maurten gels use a unique hydrogel matrix that allows higher carb intake without GI distress (up to 90g/hour). More expensive but evidence-based for serious athletes.

Most gels are 1:1 or 0.8:1 glucose-to-fructose ratios. The mixed-sugar combo allows higher total absorption than pure glucose.

Practice with the brand you'll use. Different gels have different textures, sweetness levels, and tolerance profiles. Race day isn't the time to try a new brand.

Sports drinks

Gatorade, Powerade, Skratch, Tailwind, Maurten Drink Mix. Provide carbs + sodium + fluid in one product.

Typical sports drinks have 12-20g carbs per 8 oz serving. Hitting 60g/hour requires 24-32 oz of sports drink per hour, which is a lot of fluid.

Many athletes combine: sports drinks for hydration, gels for the carb concentration.

Energy chews and gummies

Clif Bloks, GU Chews, Honey Stinger Energy Chews. ~25-30g carbs per pack.

Easier on the stomach than gels for some people. Slower to consume during running.

Real food

Bananas, dates, gummy candy (Sour Patch Kids are notoriously popular), pretzels. Cheaper than gels. Tested and used by many recreational marathoners.

For durations longer than 4 hours, real food often becomes preferable to gels — gel fatigue is real.

How to time it

First 30 minutes: Don't wait until you feel low. Start fueling within the first 30-45 min of the race. Take a gel or 8-12 oz of sports drink at this point.

Every 25-35 minutes after: Take 25-30g carbs. Most athletes settle into a cadence of 1 gel + sports drink rotation, or sports drink continuously with gels at intervals.

Practice the cadence in long training runs. The timing should be automatic on race day.

How to hit 60-90g/hour without GI distress

The gut isn't naturally trained to absorb 60+g of carbs per hour during exercise. Training the gut is part of marathon preparation:

Weeks 12-16 before race: Practice taking 30g/hour during long runs.

Weeks 8-12 before: Increase to 45g/hour.

Weeks 4-8 before: Increase to 60g/hour if targeting that level.

Final weeks: Practice your full race-day protocol (60-90g/hour) on key long runs.

Doing this is the difference between recreational marathoners who bonk and ones who don't. The legs are usually trained well; the gut often isn't.

What goes wrong

Four common mistakes:

1. Not starting fueling early enough. Waiting until mile 12 to take a gel is too late. The fueling is preventive, not responsive. Start early.

2. Taking gels without water. Most gels need to be chased with water. The concentrated sugar is hard on the gut without dilution.

3. Using unfamiliar fuels. Aid station gels you've never tried, sponsor brand sports drinks, etc. Bring your own tested fuel.

4. Skipping fluids in cold weather. Dehydration risk drops in cold weather but doesn't disappear. Sodium and fluid still matter.

Specific protocol examples

Conservative recreational protocol (sub-4 hour marathon)

  • Pre-race: Standard pre-race meal 3 hours before, banana 30 min before
  • Mile 4-5: First gel (25g carbs)
  • Mile 7-8: 8 oz sports drink at aid station
  • Mile 10-11: Second gel
  • Mile 13-14: 8 oz sports drink
  • Mile 16-17: Third gel + caffeine version
  • Mile 19-20: Sports drink + small Coke if available
  • Mile 22-23: Final gel
  • Mile 25: Whatever feels right (small Coke, fruit slice, sports drink)

Total: ~120g carbs in race + sports drinks. Roughly 30g/hour.

Aggressive trained protocol (sub-3:30 marathon)

  • Pre-race: Standard pre-race meal, gel 15 min before
  • Every 25-30 min: 25-30g gel + sports drink
  • Add caffeinated gels in second half
  • Maurten or similar high-absorption gels for the higher rate

Total: 75-90g/hour for trained athletes who have done gut training.

Real-food approach

Some athletes use bananas, dates, gummy candy, pretzels instead of gels. Works for slower-paced events where digestion is easier. Less practical at higher race paces.

What about caffeine during the race?

Caffeine during the race is well-supported, particularly in the second half:

  • Mile 15-18 of a marathon: start adding caffeinated gels (typically 20-40 mg per gel) or a small dose of cola
  • Total caffeine for the race: 100-300 mg, on top of pre-race caffeine
  • Reduces perceived effort in the final third of the race
  • Improves time-to-fatigue measurably in research

Don't introduce caffeine on race day if you don't normally consume it. The ideal pattern is to taper caffeine in the week before (down to 1-2 cups daily) to maximize race-day sensitivity.

Hydration during the race

Fluid needs:

  • Cool weather (under 60°F): 16-24 oz/hour
  • Moderate weather (60-75°F): 20-30 oz/hour
  • Hot weather (over 75°F): 24-40 oz/hour, sometimes more

Sodium intake during the race is essential, especially in heat. Sports drinks deliver some; salt tablets or electrolyte products fill gaps for heavy sweaters.

Don't over-hydrate. Drinking massive amounts of plain water without electrolytes can cause hyponatremia, which is more dangerous than mild dehydration.

What to actually do

  1. Plan for 30-60g of carbs per hour during the marathon.
  2. Practice the protocol in long training runs for 8-12 weeks before the race.
  3. Use products you've tested. Don't try anything new on race day.
  4. Start fueling within the first 30-45 minutes, not when you feel low.
  5. Pair carbs with fluid and sodium. Sports drinks or gels + water.
  6. Add caffeine in the second half if you tolerate it.
  7. Eat real food if gels stop appealing in long events.

The wall is largely preventable. Most athletes who bonk do so because of inadequate or poorly-timed fueling, not because the distance was inherently beyond them. Train the gut, plan the protocol, execute on race day. Most people finish stronger than they expect when the fueling is right.