Why Carb Loading Isn't Just One Big Pasta Dinner
While running high school and college cross country, it was common to hear the saying: "eat pasta, run fasta." The night before every big race, that meant a team dinner and a mountain of spaghetti. We called it “carb loading”. It's tradition. It's a fun pre-race ritual. It's also not really how carb loading works.
As a sports dietitian and long distance runner myself, I often get this question during race week: "So I just carb load the night before, right?" Not quite — and if that's your whole strategy, you're likely leaving performance on the table (and maybe setting yourself up for a rough morning).
Here's what's actually going on, and how to do it right.
What Carb Loading Actually Does
Your muscles store carbohydrate as glycogen, and glycogen is your body's main fuel source during endurance exercise. In a race, roughly 75% of the energy you burn comes from carbs. The catch? Your normal glycogen stores only last about 90 minutes of hard effort before they start running low.
Carb loading is simply a strategy to top off those stores before that happens — like filling your gas tank before a long road trip instead of hoping you make it on fumes. Done well, fully stocked glycogen stores can improve endurance performance by 2–3%. That's the difference between fading at mile 20 and actually having something left for the final stretch.
Why "The Night Before" Isn't Enough
Glycogen storage isn't instant. Your body needs time (and repeated carb-rich meals) to actually pack that fuel into your muscles. A single big dinner the night before your race just doesn't give your body enough runway.
Instead, think of carb loading as a 2–3 day process, not a one-time event:
Full marathon: aim for 2.5–3 days of carb loading before race day
Half marathon: a shorter window, around 1–2 days, is usually enough
Going longer than that isn't necessarily better, either. Overdoing the carb-loading window can leave you feeling stiff, bloated, and missing out on other nutrients your body needs.
How Much Do You Actually Need?
The general target is 8–10 grams of carbohydrate per kilogram of body weight per day for those 1–3 days leading into your race. For a 140 lb (64 kg) runner, that lands somewhere around 510–640 grams of carbs a day.
That number can feel overwhelming, which is exactly why most people default to "just eat more pasta." But hitting that target well means spreading carb-rich foods across your whole day (3 meals plus 2–4 snacks) using familiar, easy-to-digest foods like bagels, rice, oats, bananas, potatoes, and sports drinks. It also means backing off high-fiber, high-fat, and spicy foods that can cause GI distress right when you need your stomach to cooperate most.
The Biggest Mistakes I See Runners Make
Waiting until the night before to start — by the time dinner rolls around, there simply isn't enough time left to fully top off your stores.
Not practicing ahead of time — your carb-loading foods should get tested during training, not debuted on race morning.
Overdoing fat or fiber — whole grains, beans, and fried foods can slow digestion at the exact moment you want things moving smoothly.
Forgetting hydration — your body stores about 3 grams of water for every gram of glycogen, so carb loading without enough fluids works against you.
Skipping the shake-out run — a light run the day before can actually help with stiffness while you're loading up on carbs.
Ready to Actually Plan It Out?
Knowing what to do is one thing — building a plan around your own weight, race distance, and food preferences is another. That's exactly why I put together my free guide, Carb Loading Made Simple.
Inside, you'll find:
The exact carb targets for your body weight
A full breakdown of which foods to focus on (and which to avoid)
An easy "25-gram carb block" system so you're not doing math all week
A complete sample carb-loading day, meal by meal
👉 Grab your free copy of Carb Loading Made Simple here and walk into your next race with a fueling plan instead of just a big bowl of spaghetti.
Anna Mitchell, MS, RD is a sports dietitian, marathoner, and running coach helping athletes fuel smarter, feel their best, and actually enjoy the process.