You’ve probably heard runners go on about carb loading before race day, but here’s the thing: a lot of folks are still following advice from the 1960s that honestly makes it way harder than it needs to be. After years of trying different fueling approaches (and making plenty of mistakes), I can tell you modern science has totally changed the game. The best part? It’s actually much simpler now.
In this guide, I’ll break down how carb loading works in your body, the modern approach with real science behind it, and the practical steps you can actually follow. Whether it’s your first marathon or you’re chasing a new PR, getting carb loading right can be the difference between crashing at mile 20 or powering through to the finish.
Mastering Carb Loading for Endurance Performance
Carb loading isn’t just about scarfing down a mountain of pasta the night before the race. It’s a strategy to max out your muscle glycogen stores so you’ve got the energy to keep moving during long events. When you get it right, carb loading helps you avoid bonking and keeps you running strong all the way.
What Is Carb Loading and Why Does It Matter?
Carb loading (short for carbohydrate loading) is a nutrition trick endurance athletes use to boost the glycogen stored in their muscles before a race. Your muscles can usually stash away about 300 to 400 grams of glycogen. This is the stuff that gets you through those long miles.
The strategy really matters for races or events that last over 90 minutes. That’s when your body starts running low on glycogen. Without enough in the tank, you risk bonking or hitting the wall.
I’ve watched plenty of runners struggle in the last few miles of a marathon just because they didn’t nail their carb load. Sometimes, the difference between finishing strong and barely shuffling to the finish is all about how well you fueled up in the days before.
How Carb Loading Supports Glycogen Stores and Endurance
Your body stores carbs as glycogen in your muscles and liver. During a long race, you burn through these stores at different speeds depending on your pace. At a moderate effort (about 65% VO2 max), half your energy comes from carbs. Push harder, say 85% VO2 max, and about three-quarters of your energy comes from glycogen.
The catch? Even with full stores, you only have enough glycogen for around two hours of hard running. That’s why marathon carb loading is so crucial. By bumping your carb intake up to 70-80% of your daily calories in the days before your race, you can store more glycogen than usual.
This extra storage gives you more fuel to burn, so you can keep your pace up for longer before you start to fade.
Benefits of Effective Carb Loading
The biggest perk of carb loading is avoiding the dreaded bonk. When your glycogen runs out, your body has to lean on fat for energy, which burns slower and can’t keep you moving fast. This is why people who hit the wall slow down so much.
Good carb loading also helps with focus and coordination. Your brain needs carbs, too. When glycogen drops, mental fog and tiredness hit right alongside the physical stuff.
From what I’ve seen, athletes who get their carb load right can hold their pace longer and feel better at the finish. Recovery seems faster, too. That glycogen boost really pays off in the last part of a marathon, where things get tough for most runners.
Carb Loading Myths and the Evolution of Carb-Loading Strategies
One of the big myths is that you have to do a carb depletion phase first. The old advice was to do a long depletion run a week out, then cut carbs for a few days. The idea was that your body would rebound by storing more glycogen when you finally started eating carbs again.
Turns out, you don’t need to do this. Studies show you can just increase your carbs and cut back your training, and you’ll fill up your glycogen stores just fine. The old way just made runners feel lousy and sometimes even sick before their race.
Another myth: carb loading means stuffing yourself. More food doesn’t always help. The real goal is to make carbs a bigger part of your diet, not to eat until you’re uncomfortable. Stick to foods that are easy to digest and skip heavy, high-fiber stuff that could upset your stomach on race day.
Optimising Your Carb Loading Plan for Race Day Success
Dialing in your carb-loading plan can be the difference between a strong finish and a tough last few miles. It’s about knowing when to start, what to eat, and how to dodge the common mistakes that can throw off your race.
How to Carb Load Effectively: Timing, Amounts, and Strategy
Carb loading isn’t just one big meal, it’s a process. Start ramping up your carbs two to three days before your race, especially for half or full marathons.
The numbers help. Go for 8 grams of carbs per kilogram of bodyweight each day if you have three days. If you’re short on time, bump it up to 10-12 grams per kilo for one or two days.
If you prefer pounds, that’s about 4 grams per pound of bodyweight daily. So a 70kg runner would need around 560 grams of carbs spread out over the day.
Here’s a quick timeline for carb loading:
3 days out: Shift to 8g carbs per kilo bodyweight
2 days out: Keep carbs high, cut back training
1 day out: Continue, eat dinner early
Race morning: Get 2-3g carbs per kilo about 3 hours before the start
You’ll probably gain a pound or two during this time. Don’t stress, it’s just water (your body stores 3g of water for every gram of carbs) and means you’re fueled up.
Choosing the Best Carb Loading Foods
Not all carbs are created equal for carb loading. I stick to foods that digest easily and won’t mess with your stomach on race day.
Some top picks:
- White rice
- White pasta
- Bagels
- White bread
- Sweet potatoes (no skin)
- Oatmeal
- Pancakes
- Sports drinks
White rice and pasta are great because they’re low in fiber and go down easy. Sweet potatoes are solid, but skip the skin to keep fiber low.
Wholemeal bread and brown rice? Not ideal right before a race, the extra fiber can upset your stomach. Save those for regular training days.
Sports drinks and juice are handy for topping up your carb stores without filling you up too much. I like adding these with meals for a little extra boost.
Try to limit high-fiber foods in the last 48 hours before your race. Also, watch out for fatty foods like creamy sauces, butter, and cheese, since they slow digestion and can feel heavy.
Avoiding Carb Loading Mistakes and Pitfalls
The most common mistakes I’ve seen with carb loading can really mess up your race. First, don’t wait for the pre-race pasta dinner, one meal won’t fill your muscles with glycogen.
Things to avoid:
- Starting too late
- Overeating and feeling stuffed
- Trying totally new foods
- Eating too much fiber or fat
- Not cutting back on training
- Skipping pre-race breakfast
I always test my carb-loading plan during training, especially before long runs. Try out your strategy a few days before a big workout to see what sits well.
Don’t just pile on extra calories. You’re shifting your intake so more comes from carbs, while dialing back fat and protein a bit. The night before, have a normal-sized carb-heavy dinner. Don’t overdo it, you want to wake up hungry, not stuffed.
The Importance of Pre-Race Meals and In-Race Fuel
Your pre-race breakfast wraps up the carb-loading process. I usually eat mine about three hours before the race starts, aiming for 2-3 grams of carbs per kilogram of bodyweight.
My go-to pre-race meal? Maybe a bagel with jam, oatmeal and a banana, or some white toast with honey. I’ll throw in a sports drink too, just helps me get more carbs in without that heavy, stuffed feeling.
If it’s an early morning race, I’ll set an alarm for 3am, eat, then crawl back into bed. Sounds a bit much, but it really gives your body time to digest.
For any race longer than 90 minutes, it’s important to keep your glycogen stores up. I’ll grab an energy gel, chews, or sip a sports drink every 30-45 minutes. The goal is about 30-60 grams of carbs per hour while you’re moving.
Products that mix glucose and fructose seem to go down easier and absorb faster. I’d start fueling early, like 30-45 minutes into the race, not just when you’re dragging. Why wait until you’re running on empty?
