For races lasting longer than 90 minutes, your best nutrition strategy is to consume 30–60 grams of carbohydrate per hour (scaling to 60–90 g/hour for marathons and ultras) starting within the first 20 minutes, paired with 300–600 mg of sodium per hour. The key is practicing this exact protocol during training runs at race pace—your gut’s ability to absorb fuel while running is trainable, and race-day experimentation is the fastest route to GI distress and underperformance.

Why does fueling strategy change after 90 minutes of running?

After approximately 90–120 minutes of sustained running at race pace, your muscle glycogen stores drop below 50% of baseline levels. At this threshold, performance degrades sharply—your pace slows, perceived effort spikes, and you enter what runners call “the bonk.” While your body can oxidize fat for fuel, fat metabolism cannot supply energy quickly enough to sustain half-marathon or marathon race intensities, which typically sit at 75–90% of VO₂ max.

Research on exogenous carbohydrate oxidation shows the body can process approximately 1.0–1.2 grams of ingested carbohydrate per minute during exercise, translating to 60–72 grams per hour. This rate is limited by intestinal glucose transporters—proteins that shuttle sugar from your gut into your bloodstream. When muscle glycogen runs low, these ingested carbohydrates become your primary fuel source for maintaining pace.

This physiological ceiling is why half-marathons, marathons, and ultras require deliberate fueling strategies, while 5Ks and 10Ks do not. Shorter races finish before glycogen depletion becomes performance-limiting. Once you cross the 90-minute mark, external fuel shifts from optional to mandatory for sustaining goal pace and preventing catastrophic slowdowns in the final miles.

How many grams of carbohydrate per hour should you consume during a race?

For races between 90 minutes and 2.5 hours—most half-marathons and slower marathons—target 30–60 grams of carbohydrate per hour. Marathoners running under 3:30 and ultra-distance runners should aim for 60–90 grams per hour, using products that blend glucose and fructose. These two sugars use different intestinal transporters, allowing higher total absorption rates without overwhelming a single pathway.

Common race fuels and their carbohydrate content include:

• One energy gel: 20–25 g carbs
• One pack of chews (4–6 pieces): 24–30 g carbs
• 500 ml sports drink: 30–40 g carbs
• One stroopwafel or bar: 20–30 g carbs

Start fueling within the first 20 minutes of your race, before you feel you need it. Waiting until you’re depleted means you’re already behind—it takes 10–15 minutes for ingested carbs to reach working muscles. Maintain consistent intake every 15–20 minutes throughout the race. For a marathon aiming at 60 grams per hour, that might look like one gel every 30 minutes plus regular sips of sports drink, or two chews plus water every 20 minutes.

Your gut’s absorption capacity improves with training. Runners who regularly practice fueling during training runs can adapt to tolerate and utilize up to 90 grams per hour, while those who train fasted or neglect mid-run nutrition often experience GI distress at intake rates above 40 grams per hour. This trainability is why training plans that build fueling into long runs emphasize nutrition rehearsal as rigorously as pace work.

How much sodium do you need, and when does it matter most?

Target 300–600 mg of sodium per hour for any run exceeding 90 minutes, with intake scaling toward the upper end in hot conditions or if you’re a heavy sweater—identified by white salt crusts on your skin or clothing after long runs. Sodium serves two critical functions: it enhances carbohydrate and fluid absorption in the intestine, and it replaces electrolytes lost through sweat to maintain proper fluid balance.

Hyponatremia—dangerously low blood sodium—becomes a real risk in marathons and ultras when runners drink large volumes of plain water without adequate sodium replacement. Symptoms include nausea, confusion, swelling in extremities, and in severe cases, seizures or collapse. This condition has hospitalized and killed marathoners who over-hydrated with water alone, diluting their blood sodium to critical levels.

Practical sodium sources include:

• Salt tabs or electrolyte capsules: 100–200 mg per tablet
• Electrolyte drink mixes: 200–400 mg per 500 ml serving
• Salted pretzels or crackers: 150–300 mg per serving
• Energy gels with added sodium: 30–100 mg per packet

Most energy gels contain minimal sodium (under 50 mg), so relying on gels alone won’t meet your 300–600 mg hourly target. Pair gels with electrolyte drinks, take salt tabs every 30–45 minutes, or choose high-sodium fuel products specifically formulated for endurance events. If you notice muscle cramping in the final miles of long races, inadequate sodium is a likely culprit—cramping rarely stems from simple dehydration but rather from electrolyte imbalance.

What are the most common race-day fueling mistakes runners make?

The single biggest mistake is trying untested products on race day. Race expos hand out free samples, aid stations offer unfamiliar gels, and panic leads runners to grab whatever’s available. Your gut’s response to different carbohydrate blends, sweeteners, and textures is highly individual—what works for your training partner may leave you doubled over at mile 18. GI distress is nearly impossible to reverse mid-race once it begins.

Underfueling early and attempting to catch up late is another common error. Some runners skip the first few fuel stations feeling strong, then try to compensate after mile 16 when energy crashes. By that point, glycogen stores are depleted, and even perfect fueling can’t fully reverse the deficit. Performance suffers, and the gut is often too distressed from late overload to absorb what you’re throwing at it.

Overdrinking plain water in long races causes hyponatremia, especially in slower marathoners and ultra-runners who spend 4+ hours on course. The old “drink to thirst” advice is sound, but only if you’re also replacing sodium. Drinking beyond thirst with water alone dilutes blood sodium concentration, creating a medical emergency.

Ignoring sodium in favor of carbs alone leaves runners cramping and retaining less of the fluid they consume. Carbohydrate absorption improves when paired with sodium—your intestine uses sodium-glucose co-transporters that require both molecules. Taking in 60 grams of carbs per hour without adequate sodium means you’re not optimizing fuel delivery.

Fueling reactively instead of on a timer means you wait until you feel depleted to take a gel or chew. By the time hunger or fatigue signals register, you’re already running on fumes. Set a watch timer or plan fuel intake by mile markers—every 3 miles for a marathon, every 20 minutes for an ultra—and stick to the schedule regardless of how you feel.

How do you practice your fueling plan before race day?

Designate your weekly long run as race-simulation practice, running the final 60–90 minutes at goal race pace while executing your exact fueling protocol. Use the specific gel brand, chew flavor, and electrolyte mix you’ll carry on race day. Practice your timing—if you plan to take a gel at miles 6, 10, 14, 18, and 22 in your marathon, replicate those intervals in training. Drink the same volume of fluid at the same frequency you expect to hit aid stations.

Track which combinations trigger GI issues—bloating, cramping, urgent bathroom stops—and adjust. Some runners tolerate gels better than chews; others find liquid calories easier to process than solids. Fructose-heavy products cause distress in runners with fructose malabsorption, while high-fiber bars slow gastric emptying. The only way to identify your tolerances is repeated real-world testing under race-effort stress.

Three to four weeks of consistent fueling practice during long runs is the minimum timeline for meaningful gut adaptation. Studies show that regular carbohydrate intake during exercise upregulates intestinal glucose transporters—your gut literally grows more capacity to absorb fuel when you train it. Runners who chronically train fasted or fuel minimally in workouts often hit an absorption ceiling on race day, experiencing nausea and distress at intake levels their untrained gut cannot handle.

Some runners use “train low, race high” carbohydrate periodization—doing easy runs fasted or low-carb to enhance fat oxidation adaptations—but this strategy requires that race-simulation workouts include full race-day fueling. You cannot skip nutrition rehearsal. Runner’s Digest expert guides and structured training plans build these fueling-focused long runs into the schedule specifically because gut training is as important as muscular and cardiovascular adaptations for race-day success.

Frequently Asked Questions

Should I fuel differently for a half-marathon versus a full marathon?

For half-marathons under 2 hours, many well-trained runners can manage with 30–40 grams of carbohydrate per hour and minimal sodium supplementation if they start well-fueled. For full marathons, increase to 60–90 grams of carbs per hour and 300–600 mg sodium per hour. The longer duration magnifies glycogen depletion and cumulative sweat losses, making consistent fueling mandatory rather than optional for maintaining pace through mile 26.

Can I train my gut to absorb more carbohydrate during running?

Yes. Research demonstrates that regularly consuming carbohydrate during training runs increases both the number and activity of intestinal glucose transporters, enabling you to absorb up to 90 grams per hour without GI distress. This adaptation requires 3–6 weeks of consistent practice—taking in race-level carbs during weekly long runs at race effort. Skipping fueling practice limits your race-day capacity regardless of fitness.

What should I eat the morning of a long-distance race?

Aim for 1–4 grams of carbohydrate per kilogram of body weight consumed 3–4 hours before the start. For a 70 kg runner, that’s 70–280 grams of carbs—examples include oatmeal with banana and honey, a bagel with jam, or rice with fruit and sports drink. Choose familiar, low-fiber, low-fat foods to minimize GI risk. Top off with a gel or chew 10–15 minutes before the gun to ensure circulating blood glucose is elevated at the start.

Do I need protein or fat during a long race?

For races under 4 hours, protein and fat provide little performance benefit and slow carbohydrate absorption, potentially causing GI distress. In ultras beyond 4–6 hours, small amounts of protein (5–10 grams per hour) and fat can support satiety, preserve muscle tissue, and offer caloric variety when carb fatigue sets in. Even then, carbohydrate and sodium remain your primary fuel focus. Choose easily digestible sources like nut butter packets or recovery bars in the later miles.

How do I know if I’m taking in too much or too little sodium?

Too little sodium manifests as muscle cramps unrelated to dehydration, swelling in hands and feet, confusion, or nausea in long races—classic signs of hyponatremia. Too much sodium is rare but may cause bloating or intense thirst. If you’re a salty sweater—white residue visible on skin or clothes after runs—target 500–600 mg sodium per hour. Most runners perform well at 300–400 mg per hour in moderate temperatures, adjusting upward in heat or humidity.

Can I rely on aid station food instead of carrying my own nutrition?

Only if you’ve trained with the exact products the race will provide and confirmed your gut tolerates them at race pace. Aid station offerings vary widely—different gel brands, generic chews, pretzels, bananas, cola—and switching products on race day frequently triggers GI distress. For your first few marathons or any PR attempt, carry your own tested nutrition and treat aid stations as sources for hydration and backup calories only. Experienced ultra-runners eventually learn to use aid station variety, but that skill builds over multiple races.