Carb Loading for Endurance Athletes: How to Fuel for Race Day
Carb Loading: More Than Just the Night-Before Pasta Party
As summer starts to wind down and fall races are right around the corner, it’s time to talk about carb loading. As endurance athletes, we should be eating quite a bit of carbs every day to constantly be topping off our glycogen stores, but when it comes to race time, we need to give carbs a little extra attention.
And no, carb loading does not mean eating your body weight in pasta the night before your race. (Although, honestly, I know some of you are willing to give that a shot.) Carb loading isn’t just the pasta party the night before the race. It’s the whole week leading up to the race, really focusing in on those last 2–3 days before your race.
So, why is carb loading important? Let’s get into some of the nitty-gritty.
Our muscles need glycogen to perform. Glycogen is how our body stores glucose in the muscles (and liver). Glycogen is stored along with approximately 3–4 grams of water for every gram of glycogen. This means we want to make sure we are staying well hydrated while we are carb loading. Not only does carb loading allow us to store more glycogen, it also helps us hold onto more water. So yes, if the scale goes up a little bit during carb loading, don’t panic. You did not suddenly gain three pounds of body fat because you ate an extra bagel. A good portion of that increase is water stored along with your glycogen.
On average, athletes can store about 15 grams of glycogen per kilo of body weight. This means that a 130 lb athlete can store about 885 g of glycogen. It’s stored in both our liver and muscles. Technically, the more muscle mass you carry, the more glycogen you can store. Glycogen stored in the liver can help supply glucose to the whole body, whereas glycogen stored in the muscles primarily serves that muscle.
Why does this matter?
Because we want to start our race with a full tank, not the fuel light already blinking.
When our glycogen stores become depleted, fatigue sets in, performance decreases, perceived exertion becomes harder, etc. We want to show up to the race with as much glycogen stored as possible. This is also why we take gels (reference our earlier blog on fueling for a long run). In the case of our race, just like our long run, we want to be taking gels every 30-ish minutes to keep carbohydrate availability high. We don’t want to wait until we’ve depleted our stores to then try and dig ourselves out of that hole while we are racing. Most gels have 20–30 g of carbs in them (yes, some do have more), but adding 30 g every 30 minutes while we are working at a high intensity isn’t going to completely make up for starting the race under-fueled.
There’s an old-school philosophy that you have to completely deplete your glycogen stores before carb loading. This has since been debunked. Research shows that there is no benefit to doing this, and we can top off our glycogen stores without depleting them first. So… no reason to make yourself miserable the week before your race. Keep eating normally and knocking your workouts out.
In fact, during this taper time, keep eating as if you are still running crazy miles. It’s going to let the glycogen start to store up while we aren’t working quite as much as we normally are.
Less running + the same fueling = your body has more opportunity to store those carbs for race day.
To get really science-y for a minute, but also keep it simple: our bodies need ATP (the energy our muscles use) for muscle contractions. There are three different energy systems our bodies use to produce ATP, and for endurance athletes, the oxidative (aerobic) system is the primary one. Both carbohydrates and fat can be used to produce ATP, but they work at different rates. Fat can provide a lot of energy, but carbohydrate can provide energy much faster. And the higher the intensity, the more our bodies rely on carbohydrates—whether you are on the bike or running.
Think of it this way: fat is the slow-burning log, and carbohydrate is the kindling.
Fat is great for providing energy over a long period of time, but when we ask our bodies to run faster, we need energy fast. That’s why carbohydrate becomes increasingly important as intensity goes up. If you don’t have enough carbohydrate available, your body has a harder time producing ATP at the rate needed to maintain that intensity, and eventually, your pace has to slow down.
How Do I Carb Load?
Your mileage is coming down, but your carbs aren’t. The week before your race, your training will taper, giving your body a chance to store more of the carbohydrates you’re eating. Now, 2–3 days before you race, you are going to start replacing more of your nutrition with carb sources.We are not adding more carbs on top of our normal diet. We don’t want to show up to the race feeling stuffed to the gills. We are shifting more of our calories toward carbohydrates by scaling back on the amount of protein and fat we are taking in. The overall calorie count is staying pretty similar to what you are used to.
Basically, we aren't trying to eat more. We are trying to eat differently. One important note, especially for women: carb loading works for women, too—as long as you’re actually hitting the recommended carbohydrate intake. If you typically eat fewer than 2,400 calories a day, you may need to increase your overall calorie intake during a carb load to get enough carbohydrates to hit the recommended 8–12 g/kg target. The issue isn’t that women don’t respond to carb loading; it’s that they may not be eating enough total carbohydrate to actually complete the protocol.
So, yes, your calories may go up during a carb load—and that’s okay. The goal here isn’t weight loss. The goal is to show up on race day with a full tank.
Here’s an example of the equation to figure out how many carbs you need:
130 lb (your body weight) ÷ 2.2 = 59 kg
At 10–12 g/kg, that athlete would be aiming for approximately:
590–708 g of carbohydrates per day.
Yes.
That is a LOT of carbs.
But when you spread it throughout the day and shift your food choices toward carbohydrate-rich foods, it is much more manageable than it sounds. Stay away from new foods in the last couple of days before you race (and definitely don’t try anything new on race day—work that all out during your training runs). Focus on carbs that don’t come along with a lot of fat. For example, pretzels instead of potato chips, pasta instead of pizza.
Another key piece to help you decide what carbs to choose: keep the fiber content relatively low. We are trying to maximize how many carbs we can eat, and fiber fills us up, as well as adds more bulk to the GI tract—not something we necessarily want right before race day.
If you just can’t bring yourself to eating that many carbs, you can consider drinking some of them—juice, sports drinks like Gatorade and Skratch. This is great because it’s also helping you get your hydration in, too.
Don’t forget that drinking is part of carb loading!
The Pre-Race Meal
This meal has multiple jobs—it needs to top off blood glucose and liver glycogen and supply fluid. After a night’s sleep, your blood sugar will be lower and liver glycogen stores will be reduced. The goal of a pre-race meal is to top those back off.
In one study, a high-carb pre-race meal improved aerobic endurance running capacity by 9%. Add a carb-electrolyte mix during the run, and it improved by 22%–Pretty good reason to eat breakfast!
It’s all about timing in the morning:
3-4 hours before your race, you want about 1–4 g of carbs/kg and 0.15–0.25 g of protein/kg.
2 hours before your race, aim for 1 g of carbs/kg.
The closer you get to race time, the smaller the meal—favoring liquid carbs as you get close to start time.
The goal is to get to the starting line fueled, hydrated, and comfortable—not stuffed.
What Does 450+ Grams of Carbs Actually Look Like?
What does 450+ grams of carbs look like in a day without stuffing yourself silly?
Here’s one day from my last carb load. *Notice my food is gluten free because of an allergy—obviously, your diet will focus around your needs. My point is just to show that you aren’t eating an absurd amount of food—you are just focusing your calories on carbohydrates.
Breakfast — ~85 g
Purely Elizabeth Protein Oatmeal — 30 g
1 banana — ~27 g
2 Tbsp maple syrup — ~26 g
Strawberries — ~5 g
≈88 g carbs
Protein: ~10 g
Fat: ~3 g
Mid-morning snack — ~50 g
1 Schär GF bagel — ~30 g
1–2 Tbsp jelly — ~15–20 g
≈45–50 g carbs
Lunch — ~90 g
1 Mission GF wrap — ~25 g
3 oz chicken — minimal carbs
1 oz BBQ sauce — ~10–15 g
1 cup fruit — ~20–25 g
1 serving Snyder’s GF pretzels — ~20–25 g
≈80–90 g carbs
Afternoon snack — ~55 g
1 Katz GF Pop-Tart — ~35 g
½ banana — ~13 g
A few Bunny Grahams — ~5–10 g
≈50–60 g carbs
Dinner — ~110 g
2 cups cooked GF pasta — ~85–90 g
Tomato sauce — ~10–15 g
2–3 oz chicken — just enough protein
GF bread/roll — ~20–25 g
≈115–125 g carbs
Before bed — ~50 g
2 rice cakes + honey — ~25 g
Bunny Grahams — ~20–25 g
≈45–50 g carbs
And there you have it: a full day of carb loading without feeling totally stuffed.
The Bottom Line
Carb loading is not about one giant plate of pasta the night before your race. It’s about spending several days intentionally maximizing your carbohydrate intake while your training volume is decreasing. You are running less, which means you are using less glycogen, while continuing to give your body the carbohydrate it needs to replenish and store it.
The goal is simple: show up to the starting line fueled, hydrated, and ready to use the fitness you worked so hard to build.
And remember, carb loading is not something you should experiment with for the first time during race week. Practice it during your training. Figure out which foods sit well, how much you can comfortably eat, and what timing works best for you.
Then, when race week comes, you already know what works.