Carb Loading Before Race Day: What It Actually Is and How to Do It Right

Carb Loading Before Race Day: What It Actually Is and How to Do It Right

By MJ | March 2026

I want to be upfront about something: I'm a bodybuilder, not an endurance athlete. My training is built around hypertrophy, strength, and competition prep and my clients are primarily lifestyle clients. Carb loading for me looks very different than it does for someone running 100 miles.

But I'm also a certified nutrition specialist, and I've spent the last few years watching Spencer train for and race ultramarathons, a Half Ironman, and now a 100-miler. Being that close to it, tracking his nutrition, prepping his food, understanding what his body is doing at mile 51, has given me a real education in endurance nutrition that I couldn't have gotten any other way.

So when I write about carb loading, I'm writing as someone who understands the science and has watched it play out in real time. Not as someone who's done it herself, but as someone who has been deep in it alongside Spencer for years.

Here's what I've learned.

What it actually is

Your muscles store carbohydrates as glycogen. Glycogen is your primary fuel source during sustained effort. The problem is your muscles can only hold so much, somewhere between 300 and 500 grams depending on your size and training status. For shorter efforts, that's fine. For a 100-mile race, you will deplete those stores multiple times over.

Carb loading is the deliberate process of maximizing glycogen stores before a long race so you start with a full tank. The longer the event, the more it matters.

When to start

The "night-before ungodly amount of pasta" dinner is a myth guys. You're going to be in a world of hurt come race morning. Your muscles can only absorb and store so much glycogen at one time. Loading has to happen over two to three days to actually saturate your stores.

Here's how the timeline breaks down:

Three to four days out, training volume drops. You're in taper. Start increasing carbohydrate intake and shifting the composition of your meals so carbs make up a larger portion of each one.

Two days out, carb intake is at its peak. This is the day to be most deliberate about hitting your targets.

The night before, keep it moderate and familiar. Nothing heavy, nothing new. A meal that sits well and digests cleanly is more valuable than the largest plate you can put together.

For Spencer, that will likely be chicken and rice and coconut aminos. It's our go-to in this house.

Race morning, eat a moderate carbohydrate meal a few hours before start. Simple, digestible, and something you've eaten before a long training run.

What to eat

This is where most people get it wrong. Carb loading doesn't mean junk food or anything your body isn't used to. The best options are whole food carbohydrate sources that digest well and don't cause GI issues: oatmeal, white rice, sweet potatoes, potatoes, fruit, whole grain bread. Foods your body knows how to process.

What to avoid during this window: anything high in fat, anything extremely high in fiber, anything new or unfamiliar. Fat slows digestion. High fiber increases gut activity. Both can become problems when you're 12 hours into a race and your digestive system is already under stress.

How much

The research supports somewhere between 8 and 12 grams of carbohydrates per kilogram of body weight per day during the loading phase. For someone 180-pounds, that's about 650 to 980 grams of carbohydrates per day. To put that in context: a cup of cooked white rice is about 45 grams. A medium banana is about 27 grams. You have to be intentional and consistent across every meal, not just dinner.

For reference, during my last bodybuilding prep, my highest carb day got up to 600g at 122 lbs. I get how intentional you have to be to eat that much!

Hydration and sodium

This part gets overlooked. For every gram of glycogen your muscles store, they also store approximately three to four grams of water. This is why athletes often see a small weight gain of two to four pounds during the loading phase. That is not fat. It's water bound to glycogen, and it's exactly what you want going into a race.

Because of this, sodium matters during carb loading. It helps your body hold onto that fluid. Electrolytes in the morning, consistent fluid intake all day, and sodium with meals are all part of the protocol.

The biggest risk: GI distress

The number one reason carb loading fails on race day is stomach issues. Too much fiber, too much fat, an unfamiliar food, or a meal that was just too large. The fix is simple: race week is not the time to try something new. Eat foods you've eaten before long training runs. Keep portions reasonable. Be especially careful the night before and race morning.

What it doesn't do

Carb loading doesn't replace on-course fueling. At 100 miles you will still deplete your stores no matter how well you loaded. Carb loading gets you started full. After that, consistent fueling throughout the race keeps you moving.

It also doesn't fix a training block that wasn't there. Loading glycogen into muscles that aren't conditioned to use it efficiently won't save you. The foundation always comes first.

The short version

Start two to three days out. Prioritize whole food carbs: oatmeal, rice, fruit, potatoes. Keep fat lower during the loading window. Maintain protein. Hydrate consistently and stack electrolytes daily. Keep the night-before and race-morning meals simple, familiar, and easy to digest.

-MJ