Carb Loading by Race Distance: Half-Marathon and Marathon

Most runners carb load before every race. Science says most of them do not need to.

Not every race requires extra fuel. But when it does, the difference is real.

Your body stores enough fuel for roughly 75 to 90 minutes of hard running. Below that threshold, your normal diet handles it. Above it, you need a plan.

Here is what this guide covers:

• Which race distances need carb loading
• Pre-calculated targets by body weight (zero math required)
• The modern loading protocol (no depletion phase)
• What to eat, what to skip, and how to avoid race-morning bloating

Key Takeaways

– 5K and 10K runners do not need to carb load. Normal eating covers these distances at any pace.
– Half-marathon runners racing over 90 minutes should load for 24 hours. Under 90 minutes, emphasize carbs the day before.
– Marathon runners need 24 to 48 hours of structured loading. Target 6 to 10 grams per kilogram of body weight, scaled by experience. Only proven elite loaders should push above 10.
– The old depletion phase is unnecessary. One focused day of high-carb eating matches the old multi-day approach.
– Gut comfort beats perfect numbers. When in doubt, go lower.

Do You Actually Need to Carb Load?

Your muscles and liver store roughly 500 grams of carbohydrate. That is enough fuel for about 75 to 90 minutes of moderate-to-hard running.

If your race is shorter than that, your tank is already full from normal eating.

When those stores run low, your body shifts to burning fat. Fat burns too slowly to hold your target race pace. That is the wall. Carb loading delays it by topping off your fuel stores before the gun goes off.

Modifiers that change your target:

• GI issues during racing: Cap loading 2 g/kg below your tier target. With severe GI history, hard cap at 7 g/kg regardless of tier.
• First time carb loading: Stick to the lower end of your range. Your gut has not practiced processing this volume yet.
• Larger athletes (85+ kg): Cap at 8-9 g/kg. Higher daily totals become impractical to eat.

Gut comfort beats perfect numbers. When in doubt, go lower.

Your Pre-Calculated Carb Targets

Find your weight. Find your target. Done.

A 75 kg runner targeting 10 g/kg needs 750 grams of carbs. That is not a pasta dinner. That is an entire day of focused eating.

The modern protocol

The 7-day depletion-and-loading protocol is outdated.

A 2002 study found that a single day at 10 g/kg with minimal exercise matched the old multi-day approach in trained endurance athletes. No starving yourself. No depletion runs.

A large review of 181 muscle biopsy studies confirmed two factors that predict fuel storage above all else. Your fitness level and how many carbs you eat beforehand.

Fitter runners have greater storage capacity. Research consistently shows 2 to 3 days of high carb intake paired with a taper fills the tank.

Most runners obsess over which gel to take at mile 18. The more impactful variable is the 24 hours before the gun goes off.

The Loading Timeline

Why the activation session matters

That easy run or set of strides the morning before your race is more than a shakeout. A brief exercise appears to prime your muscles to absorb and store more fuel.

Think of it as opening the door before filling the tank. A short activation session in the morning, then aggressive carb intake the rest of the day.

If you have never carb-loaded before, consider spreading intake across 36 hours instead. Your gut will thank you.

What to Eat

Loading-friendly foods:

• White rice, white bread, bagels, pancakes with syrup, pretzels
• Honey, jam, maple syrup, fruit juice
• Gummy bears, jelly sweets, hard candy (pure sugar, zero fiber, easy to top up)
• Bananas, rice cakes, low-fiber cereals
• Liquid carbs are underused. A tall glass of apple juice delivers roughly 55 to 60 grams of carbs.
  • SiS BETA FUEL 80 Powder provides 80 grams of carbs per serving. One of the most efficient ways to hit your target without feeling stuffed. 
  • SiS GO Energy Powder delivers 47g of carbs per serving and works well for adding liquid carbs between meals.

What to Skip

• Whole grains, bran, high-fiber cereals (fiber fills you up before your fuel stores do)
• Raw vegetables and salads (bulky, low-carb density)
• Beans and legumes (gas producers during race week)
• Heavy sauces, cheese, cream, and high-fat foods (fat slows digestion)
• Large portions of meat or protein-heavy meals (not the priority)
• Alcohol (hurts hydration and sleep when both matter most)
• Anything new or spicy (race week is the wrong time to experiment)

Simple sugars pack more fuel per bite than complex carbs. Lower fiber means less fullness and more room for carbs.

Common myths about carb loading

“Will carb loading make me gain weight?”

Temporarily, yes. Water follows stored carbohydrate into your muscles. Expect 1 to 2 kg on the scale. It is fuel, not fat. It disappears during the race.

“Is the pasta dinner enough for my marathon?”

Probably not. A single pasta dinner provides roughly 200 grams of carbs. A 70 kg runner targeting 10 g/kg needs 700 grams. You need an entire day of carb-focused eating, not one big meal.

“What about the depletion phase?”

Outdated protocol. Research showed you can match the same loading from 24 hours of high-carb eating without depleting first.

“I always feel bloated race morning.”

• Spread carbs across the full day instead of one giant dinner.
• Lean on liquid carbs and simple sugars. They digest faster and take up less space.
• Watch sodium from loading foods like sports drinks and pretzels. Excess sodium causes water retention.
• Sip water throughout the day to support fuel storage.

What to do next

Your race distance and finish time determine whether carb loading matters. For most runners at most distances, it does not.

For half-marathon runners over 90 minutes and all marathon runners, a focused 24 to 48 hours of high-carb eating changes the race. Carb loading is not about the pasta dinner. It is about the whole day before.

Start with the lower end of your target range. Practice your loading protocol before a long training run. Adjust from there.

The modern protocol is simple: taper, activate, load, race.