Race day GI disasters are preventable. Not by finding the “right” gel or the “best” pre-race meal, but by practicing your entire nutrition plan during training until it’s boring and predictable.

The research is unambiguous: GI problems during endurance races correlate strongly with consuming unfamiliar foods and fluids.[1] Runners who practice their race nutrition during training have significantly fewer GI issues on race day.

The Pre-Race Meal

Timing: 2-3 hours before the gun. This gives your stomach time to empty most of the food before running.

Composition: Carbohydrate-heavy, moderate protein, low fat, low fiber. Examples: oatmeal with banana, toast with jam, a bagel with a thin layer of peanut butter, plain pancakes.

Portion: 300-600 calories depending on your body size and the race distance. More for a marathon, less for a 5K. You’re topping off glycogen, not eating a feast.

The rule: Eat the same pre-race meal before at least 3-4 long runs or quality sessions during training. By race day, your stomach should have zero surprises.

During the Race

5K and 10K

No fueling needed. Water at aid stations if thirsty. Don’t carry gels.

Half Marathon

Most runners can complete this distance without fueling, but a gel at miles 7-8 provides a small performance boost in the final miles. If you plan to take one, practice it during training long runs.

Marathon

Fueling is mandatory. Target 30-60 grams of carbohydrates per hour starting at mile 5-6 (not mile 1 — you have plenty of glycogen early). This means approximately one gel every 30-45 minutes.

Know the course aid stations. What brand of sports drink do they carry? What gels are available? If you plan to use course nutrition, train with those exact products. If you prefer your own, carry them.

Carry your own vs. course nutrition: Carrying 4-6 gels adds minimal weight. It guarantees you’re using products you’ve tested. Course nutrition is convenient but risky if you haven’t trained with it.

Carb Loading

Carb loading — increasing carbohydrate intake in the 1-3 days before a long race — has evidence for events lasting 90+ minutes. It maximizes glycogen stores, delaying the point where you need to rely on mid-race fueling.

How: Increase carbohydrate intake to 8-10 grams per kilogram of body weight per day for 2-3 days before the race. This doesn’t mean eating more total food — it means shifting the macronutrient ratio toward carbohydrates. Less protein and fat, more pasta, rice, bread, and potatoes.

When it matters: Marathon and half marathon. Possibly long trail races.

When it doesn’t: 5K and 10K. These events don’t deplete glycogen enough for carb loading to make a difference.

When it hurts: If you eat dramatically more than usual, GI distress follows. Carb loading is a ratio shift, not a volume increase. “I’m carb loading” is not an excuse to eat until you’re uncomfortable.

The Morning-Of Checklist

  • Eat your practiced pre-race meal 2-3 hours before the start
  • Drink 16-20 oz of water 2-3 hours before, then sip as needed
  • Avoid coffee if you don’t normally drink it (don’t try it for the first time on race day). If you always drink coffee before runs, maintain the routine.
  • Have your race nutrition (gels, chews, sports drink) ready and accessible — safety-pinned to shorts, in a belt, or in pockets you’ve tested
  • Last bathroom visit 30-60 minutes before the start

Everything on this list should have been practiced multiple times during training. Race day is execution, not experimentation.