Carb Loading Explained (2026): The Modern 2-3 Day Protocol

A full glycogen store is roughly 400-500 g of carbohydrate in muscles and 80-100 g in the liver. At marathon pace, a 70 kg runner burns about 350-400 g of carbs across 26.2 miles. Start depleted and you're handing yourself a bonk at mile 20.

The question is how to start the race with full stores. The answer used to be a seven-day process. In 2026, it's a weekend.

How we got here

The original protocol (1960s-70s) had athletes do a long depleting run 6-7 days out, then eat low-carb for 3 days, then switch to high-carb for 3 days. The depletion phase supposedly made muscles "store more" when carbs came back in. It also made athletes miserable — low energy, bad sleep, poor workouts — during a critical week.

Research since the early 2000s, particularly Bussau et al. (2002) and Tarnopolsky et al. (2005), showed trained athletes fully saturate glycogen with 24-36 hours of high-carb intake, no depletion needed. The old protocol got quietly retired in serious coaching, though it still shows up in old marathon books.

The modern protocol

1. Days 7-3 before race: eat normally. Protein, carbs, fat at usual ratios. You're tapering mileage, so total calories drop slightly. Nothing unusual.
2. Days 2-1 (24-36 hours out): shift to 10-12 g/kg/day of carbs. For a 70 kg runner, that's 700-840 g of carbohydrate. Low fibre.
3. Night before race: moderate dinner at 6-7 pm. Most of the load is already in.
4. Race morning: 1-2 g/kg breakfast 3-4 hours before start.

What 10-12 g/kg actually looks like

Hitting 700-840 g of carbs is harder than runners expect. A full cup of cooked pasta has about 45 g of carbs. A bagel has 50-55 g. A banana has 25 g. You need to eat a lot.

A sample load day for a 70 kg runner:

Meal	Example	Carbs
Breakfast	Oatmeal (large bowl) + banana + honey + toast with jam + orange juice	~140 g
Mid-morning	Bagel with honey + sports drink 500 mL	~85 g
Lunch	White rice + grilled chicken + bread + apple	~140 g
Afternoon 1	Pretzels + sports drink	~90 g
Afternoon 2	Rice cakes + jam	~75 g
Dinner	Pasta with olive oil + bread + lemonade	~150 g
Evening	White toast with honey + small glass of juice	~60 g
Total		~740 g

Low-fibre, not no-fibre

The reason to go low-fibre is GI residence time. Fibre stays in the gut 24-30 hours. If you're loading two days out and eating lentils, half of that lentil meal is still in your colon at the gun. That's how mile 13 ends up being a porta-potty.

Choose "beige carbs" for the load window:

• White rice, white bread, bagels, white pasta
• Pretzels, rice cakes, crackers
• Pancakes, waffles
• Bananas (ripe, yellow/brown)
• Honey, maple syrup, jam
• Sports drink, maltodextrin mix, fruit juice
• Oatmeal (rolled, not steel-cut)
• Potatoes (peeled)

Skip during the 36-hour window:

• Beans, lentils, chickpeas
• Raw salads, broccoli, cauliflower
• Whole-grain everything (use white during load)
• Bran cereals
• Apples with skin (ok peeled, but not necessary)
• Dairy if you're lactose-sensitive (add GI risk)
• Anything new to you

The water weight is intentional

Glycogen binds roughly 3 g of water per g of carbohydrate. If you add 300 g of glycogen to your muscles and liver during loading, you also store about 900 g of water. That's the 2-4 lb "sudden weight gain" some runners panic about the morning of the race.

This water is useful. It's the reserve that helps with cooling and hydration during a long race. You don't want to avoid it. Don't cut water intake to "avoid the bloat."

Modifications

For shorter races

Half-marathon: a carb-forward day two days out is sufficient for most runners. 10K and under: don't need any special loading beyond a normal pre-race dinner.

For ultras

Most ultra-runners do a slightly milder 3-day version at 8-10 g/kg/day for 48-72 hours. Reason: the race is long enough that in-race fueling matters more than starting glycogen, and the milder load causes less GI discomfort on race morning.

For gluten-free runners

Same protocol, different foods. White rice, corn tortillas, potatoes, gluten-free oats, gluten-free pasta, bananas, honey, fruit juice, rice cakes.

For diabetics

Work with your endocrinologist. The protocol as written will spike blood sugar; insulin dosing and timing need adjustment. Not a DIY situation.

Common mistakes

1. Front-loading too early. Eating 800 g of carbs on Thursday for a Sunday race stores poorly and adds GI risk.
2. High fibre during the load. Classic "bean chili because it's carb-heavy." Bad idea.
3. Alcohol at the expo dinner. Dehydrating, disrupts sleep, and displaces useful calories.
4. Panicking about weight gain. 3 lb of water is the plan working. Don't restrict morning-of fluids to "lose the bloat."
5. Trying new foods. Never. Everything on your load plate should have been eaten before a long run at least twice.

What carb loading won't do

It won't make a slow runner fast. It won't replace proper training. It won't compensate for bad pacing or missed long runs. What it does is take a finishable race and make the last 10K less awful — potentially worth several minutes for a marathoner, potentially the difference between finishing and DNF for a first-timer.

Late-April 2026 spring marathon notes

With the spring marathon block now in full swing — Boston is in the rearview, London just ran, and the late-April / early-May regional marathons are this weekend — the most common mistake we are seeing in athlete logs is the "front-loaded Thursday" pattern: trying to hit 10 g/kg three days out instead of the protocol's 24-36 hour window. Two days of bloated, sluggish training does not buy you any extra glycogen. Save the load for the final 36 hours and run the rest of taper week on normal calories.

Related

• Marathon Nutrition Guide — the full race-day playbook
• Marathon Fueling Calculator — in-race targets
• High-Mileage Training Nutrition — daily baseline
• Gels vs Real Food — in-race options