What every runner should know about fueling with carbs.

No one talks about calories per hour anymore, it's all about carbs. Carbs = immediate energy while calories is = general energy which might not be immediately available. Here's what you need to know and products to help keep you from the dreaded bonk.

How Carbs Fuel Your Runs

Carbohydrates are your body’s main fuel source when running. But not all carbs are created equal. Here's what you need to know:

1. Simple Sugars (like glucose, sucrose, fructose)

• Fast-acting fuel
• Great for quick energy
• Found in maple syrup, candy, and many sports drinks

2. Complex Carbs (like maltodextrin)

• Slower, sustained energy 
• Gentler on the stomach for some
• Common in endurance fuel products

Your body breaks these down into glucose, which your muscles use to keep you moving. Many endurance products combine sugar types to use multiple pathways (fructose and glucose use different transporters in your gut), allowing you to absorb more carbs per hour without overloading your stomach. Often you'll here about the ratio 1:0.8 referring to the Glucose to Sucrose. Let me explain why this is: 

Your body can only process so many carbs at once. The breakdown of maltodextrin (very popular corn derivative) into usable glucose occurs in the small intestine using enzymes in both saliva and from the pancreas. This is only one pathway and is believe that the body can use about 60g/hr. Often fructose is paired with maltodextrin because it uses a different absorption pathway as it breaks down to usable glucose. Roughly 70 percent is absorbed by the liver and the rest through the small intestines. You can really nerd out on this but the idea is that a couple different sources of glucose results in higher carbohydrate absorption.

How to Avoid Gut Distress

"Gut bombs" are no fun—and they usually come from poor fueling strategy. Often runners try to consume too much at a high intensity and their stomach kicks in a stress response which is to eliminate whatever is in the gut (the focus of the body is elsewhere).

 Here’s how to stay comfortable while keeping energy up:

Start small: Don’t overload your stomach during short runs.

Practice: Train with the same fuel you'll use on race day. At the very least, the same carb intake and intensity. Training with fancy pre-packaged fuel is expensive.

Hydrate smart: Some drink mixes have higher sodium to help absorption and replace sweat losses.

Mix it up: Use both fluids and solid carbs depending on your intensity and duration.

Fuel Comparison Table

Here’s a breakdown of popular drink mix products available at White Mountain Ski Co, with info on their carb content, sugar sources, sodium, and price:

📌 Tip: Products that use multiple carb sources (like maltodextrin and fructose) allow your body to absorb more carbs per hour—great for longer runs.

Final Tips

• For short runs (<60 min): Hydration + small carbs is enough.
• For longer runs (1–3 hours): Aim for 30–60g carbs/hour.
• Over 3 hours? Start practicing up to 90g/hour using mixed carb sources.

Experiment during training, not on race day. Everyone’s stomach is different—find what works for you.