5 Race-Day Fueling Mistakes That Will Wreck Your Marathon

You trained for 16 weeks. Your legs are ready. But race day still goes sideways because of what you ate (or didn't eat) during the run. Here are the five fueling mistakes that ruin more marathons than undertrained legs.

1. Trying Something New on Race Day

This is the golden rule of race nutrition, and people still break it constantly. That free gel at mile 8? Skip it if you've never tried that brand. The sports drink on course? It might not be what your stomach expects.

Practice your exact fueling plan during at least 3–4 long training runs before the race.

2. Starting Fueling Too Late

By the time you feel hungry or low on energy, you're already behind. Glycogen depletion is a slow process, and gels take 15–20 minutes to hit your bloodstream.

Start taking in carbs by mile 4–5 of a marathon. Aim for 60–90g of carbs per hour for efforts over 2 hours.

3. Not Drinking Enough Water With Gels

Gels are concentrated carbohydrate. Without water, they sit in your stomach and cause cramping, nausea or worse. Every gel should be followed by 4–6 oz of water.

Conversely, don't wash gels down with sports drink. That's a double dose of sugar that can overwhelm your gut.

4. Ignoring Sodium

Sweat contains sodium, and as you lose it, your muscles lose their ability to contract efficiently. This is a major cause of late-race cramping.

Aim for 300–700mg of sodium per hour, depending on your sweat rate and conditions. Salt tabs, electrolyte drinks or salty snacks all work.

5. Going Out Too Fast and Burning Through Glycogen

This is a fueling mistake disguised as a pacing mistake. Running the first half too fast burns glycogen at a dramatically higher rate, which means you'll deplete your stores before mile 20 no matter how many gels you take.

Stick to your goal pace from the start. Negative splits are always better than positive ones.

Build Your Plan

Use our Fueling Planner to build a mile-by-mile nutrition schedule based on your goal time, body weight and race conditions. It's free and takes about 30 seconds.