How to Practice Race Fueling on Long Runs

Your fueling plan on race day is only as good as your practice. You can map out the perfect gel schedule—right brand, right carb target, right timing—and still blow up on race day if your gut hasn't rehearsed the protocol under stress.

The runners who master race fueling aren't the ones with the best spreadsheets. They're the ones who've spent their long runs training their gut to absorb 80-100g of carbs per hour at effort. Unfortunately, many runners skip this. They dial in their paces, hit their mileage, but treat fueling as an afterthought until race week. Then they show up on race morning with a fueling strategy never practiced at marathon pace.

This is the guide to not being that runner.

Why your gut needs training (not just your legs)

Your gastrointestinal system adapts to carbohydrate intake the same way your cardiovascular system adapts to mileage—gradually, with consistent stimulus. The science behind high-carb fueling is clear: dual-source carbohydrates (glucose + fructose) allow absorption rates of 90-120g per hour. But that's a ceiling, not a starting point. An untrained gut trying to process 90g/hr for the first time will fight back with cramping, bloating, or worse.

Research from Asker Jeukendrup's lab has shown that gut training, consistently practicing high-carb intake during exercise, increases the number and activity of intestinal carbohydrate transporters within 2-4 weeks. Your gut literally builds more infrastructure to absorb fuel. Skip the training, and you're asking a two-lane road to handle highway traffic.

The practical takeaway: start fueling practice early in your training block, not during the last few long runs before taper. You need at least 6-8 sessions of progressive fueling to build real tolerance.

Start low, build systematically

If you've never practiced structured fueling on long runs, don't start at your race target. Here's how to build up:

Weeks 1-2:Start at 40-50g of carbs per hour. This is conservative, and that's the point. You're teaching your stomach to accept fuel at effort, not testing its limits. One gel every 30-40 minutes, depending on the brand.

Weeks 3-4:Move to 60-70g per hour. This is where most runners hit their first friction—a bit of sloshing, some mild discomfort. That's normal. Your gut is adapting. If it's genuinely painful, hold at this level for another week before pushing higher.

Weeks 5-8:Push toward your race target: 75-90g per hour (or higher if you're experienced). By now, your gut should handle this without distress. If you're still struggling at 75g, that's useful information—it means your race plan needs to reflect that reality, not ignore it.

The progression matters more than the final number. A runner who builds to 80g/hr over eight long runs will have a far better race day than one who attempts 100g/hr for the first time during their 20-miler.

Match the conditions, not just the distance

The biggest mistake in fueling practice is treating it as a calorie exercise detached from race conditions. Your gut doesn't operate in a vacuum—effort level, heat, hydration, and pacing all affect how well you absorb carbs.

Three things to simulate:

1. Race effort, not easy-run effort.Fueling at 9:00/mi pace on a casual long run tells you almost nothing about fueling at 7:30/mi on race day. The blood flow to your gut drops significantly as exercise intensity increases. Practice fueling during the marathon-pace segments of your long runs—the 3-6 mile pickups at goal pace, along the warm-up miles.

2. Heat and humidity.If your race could be warm (Boston in a warm year, Chicago, any fall marathon with an unlucky forecast), do at least two long runs with fueling practice in warmer conditions. Heat diverts blood flow from your skin to cool it, which means even less blood flow for digestion. A fueling plan that works at 45°F can fall apart at 65°F.

3. Hydration pairing.Practice drinking water or a sports drink with your gels the same way you will on race day. If you're planning to grab cups at aid stations, practice sipping from a cup while running. If you're carrying a handheld, train with the handheld. The mechanical act of drinking while running at effort is its own skill, and fumbling it on race day wastes time and disrupts your fueling rhythm.

Use your exact race products

This sounds obvious, but it's the most common fueling mistake in marathon training: practicing with one product and racing with another.

Your gut adapts to specific carbohydrate formulations. The ratio of glucose to fructose, the osmolality, the consistency—all of it matters. Maurten's hydrogel technology sits differently in your stomach than a GU. SiS Beta Fuel's 1:0.8 maltodextrin-to-fructose ratio processes differently from Spring Energy's rice-based formula.

Pick your race gel early in your training block. Then use it for your long runs from that point forward. If you're planning to use a caffeinated gel for the final 10K (a solid strategy), practice that switch at least twice during training.

The same goes for on-course nutrition. If your race provides Gatorade Endurance at aid stations and you've been training with Maurten drink mix, you have a mismatch. Either bring your own drink mix on race day or practice with what'll be on the course.

Build your timing protocol

Race fueling isn't just about how much—it's about when. And the timing needs to be automatic by race day.

My protocol: first gel at 20 minutes, then every 25-30 minutes after that. I don't wait until I feel like I need it. By the time you feel low on energy during a marathon, you're already 20-30 minutes behind on carbs. That's a deficit you won't recover from.

Practice the same timing on your long runs until it's reflexive. You should be reaching for a gel because your watch says it's time, not because your legs are starting to fade. After 6-8 practice sessions, the timing becomes muscle memory. You won't even think about it on race day—which is exactly the point, because on race day, you want to be thinking about pacing and competitors, not fumbling through your vest wondering when you last ate.

One thing that helps: set a repeating timer on your watch. Every 25 minutes, it buzzes. You take a gel. No decision-making required. I've used this in every marathon since switching to high-carb fueling, and it removes one more variable from an already complex day.

The long run fueling checklist

For every long run over 14 miles during your training block:

• Bring your race gels (not a random brand from the drawer)
• Set a repeating timer at your planned race interval (20-30 min)
• Practice at race effort for at least a portion of the run
• Take in water or sports drink with each gel
• Note how your gut responded afterward

That's it. No special equipment, no lab testing, no overthinking. Just consistent practice with the products you'll race with, at the effort you'll race at, on the schedule you'll race on.

The bottom line

Race fueling is a skill, and skills require practice. Your long runs are the rehearsal—use them. Start early in your training block, progressively increase your carb intake, simulate race conditions, and stick with your race products. By the time you're standing in the corral on race morning, fueling should be the one thing you're not worried about.

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