Fueling a marathon well comes down to three phases: loading your muscles with energy in the days before the race, replacing carbohydrates and fluids while you run, and recovering smartly afterward. Each phase has specific targets backed by sports nutrition research, and getting them right can be the difference between a strong finish and hitting the wall at mile 20.
Carb Loading Before the Race
Your muscles store carbohydrates as glycogen, and a full tank holds roughly enough energy to fuel about 90 minutes of hard running. Since most people take three to five hours to finish a marathon, topping off those stores beforehand is essential. The target is 10 to 12 grams of carbohydrate per kilogram of body weight per day for the 36 to 48 hours before race morning. For a 70 kg (154 lb) runner, that works out to 700 to 840 grams of carbs per day.
That’s a lot of pasta. To hit those numbers, you’ll need to make carbohydrates the centerpiece of every meal and snack: white rice, bread, pancakes, pretzels, fruit juice, and sports drinks all count. This isn’t the time for whole grains and big salads. High-fiber foods slow digestion and increase the risk of stomach problems on race day, so switch to lower-fiber, easily digestible options. You should also cut back on fat, protein, and dairy in those final one to two days, since all three slow gastric emptying and can trigger gastrointestinal distress during the race.
What to Eat Race Morning
Your pre-race meal tops off liver glycogen, which gets depleted overnight while you sleep. Eat two to four hours before the gun goes off, aiming for a carbohydrate-rich, low-fiber, low-fat meal. A common approach is a plain bagel with jam, a banana, and a sports drink. Keep protein minimal and avoid anything you haven’t tested in training.
The exact amount of carbohydrate depends on how much time you have before the start. With three to four hours, you can handle a larger meal (around 2 to 3 grams of carbs per kilogram of body weight). With only two hours, keep it smaller and stick to simple carbs that digest quickly. If your race starts early and eating a full meal at 4 a.m. sounds miserable, a smaller snack closer to the start still helps, as long as you carb-loaded well the day before.
Fueling During the Race
Once you’re running, your goal is to replace some of the carbohydrate you’re burning. The baseline recommendation is 30 to 60 grams of carbohydrate per hour for the first couple of hours. If your race will last longer than two and a half hours (which it will for most runners), guidelines suggest pushing toward 60 to 90 grams per hour. Some elite and experienced runners go even higher, above 120 grams per hour, but that level of intake requires significant gut adaptation.
Where those carbohydrates come from matters. Your intestines absorb glucose and fructose through different pathways, so products that combine both sugars allow you to take in more total carbohydrate without overwhelming either system. Research shows the fastest absorption and best performance come from a fructose-to-glucose ratio of roughly 0.8 to 1. Most commercial gels and sports drinks designed for endurance events already use this kind of blend (often listed as maltodextrin plus fructose on the label).
In practical terms, this means consuming one to two gels or a few big swigs of a carbohydrate drink every 20 to 30 minutes. Start early. Many runners wait until they feel tired, but by then glycogen is already running low and it’s hard to catch up. A good rule of thumb is to begin fueling within the first 30 to 45 minutes of the race and stay consistent throughout.
How Pace Changes Your Fueling Needs
A runner finishing in three hours burns through glycogen faster per minute but spends less total time on the course. A five-hour runner burns fuel at a lower rate per minute but needs to sustain energy for two extra hours. Both runners benefit from the 30 to 60 gram per hour range, but the slower runner will consume a larger total amount of carbohydrate simply because they’re out there longer. A five-hour marathoner taking in 50 grams per hour would consume around 250 grams total, compared to roughly 150 grams for a three-hour finisher at the same hourly rate. That’s a meaningful difference in how many gels, chews, or drink servings you need to carry or pick up at aid stations.
Hydration: Drink to Thirst
Older guidance told marathon runners to drink as much as possible to avoid dehydration. That advice turned out to be dangerous. Studies estimate that over 10% of marathon finishers develop some degree of exercise-associated hyponatremia, a condition where blood sodium drops to dangerously low levels, and excessive fluid intake is the primary risk factor.
The current consensus, endorsed by international guidelines since 2015, is simpler: drink to thirst. Your body’s thirst mechanism is a reliable signal during prolonged exercise, and following it keeps most runners in a safe hydration range without the risk of overdrinking. Despite this updated guidance, most marathon runners are still unaware of it, which means you’ll likely hear conflicting advice from fellow runners and even some aid station volunteers.
Sodium replacement is worth thinking about, especially if you’re a heavy or salty sweater (you’ll notice white streaks on your clothes or a gritty feeling on your skin). Sodium loss during running varies enormously between individuals and doesn’t correlate neatly with age, pace, or duration. Because of that variability, the best approach is personalized. If you’ve had cramping or excessive fatigue in past long runs, try adding an electrolyte drink or salt capsule and see how you respond. For most runners doing their first marathon, a standard sports drink at aid stations provides enough sodium alongside the carbohydrate it delivers.
Train Your Gut Before Race Day
One of the biggest mistakes first-time marathoners make is trying a fueling strategy for the first time on race morning. Your gut adapts to processing carbohydrates during exercise, and you can train that adaptation. Research on intestinal transport shows that as few as three days of higher carbohydrate intake during exercise can start increasing the gut’s ability to absorb sugars, and within two weeks the changes are significant.
Use your long training runs as dress rehearsals. Practice eating and drinking at race pace, using the exact products you plan to use on race day. Start with smaller amounts if you’re not used to eating while running, then gradually increase. This is how you figure out whether gels, chews, or liquid calories work best for your stomach before you’re 15 miles into a race with no good options. Many runners find that gels washed down with water work well, while others prefer sipping a carbohydrate drink throughout. The “best” fuel is whichever one you can tolerate consistently at your goal pace.
Minimizing Stomach Problems
Gastrointestinal distress is one of the most common complaints among marathon runners, and nutrition is typically the trigger. The main culprits are fiber, fat, protein, dairy, and overly concentrated carbohydrate solutions. Highly concentrated gels taken without enough water can sit in your stomach and cause nausea or cramping.
To reduce your risk, keep your pre-race meals and race-day fuel as simple and carbohydrate-focused as possible. Avoid anything new on race day. Cut high-fiber foods at least 24 hours before the race (some runners with sensitive stomachs benefit from reducing fiber two to three days out). During the race, take gels with a few sips of water to dilute them, and don’t double up at aid stations by taking a gel and a sports drink simultaneously, since both are concentrated carbohydrate sources.
Recovery Nutrition After the Finish
What you eat in the hours after crossing the finish line affects how quickly your muscles rebuild glycogen stores and repair damaged tissue. The window matters most in the first 30 minutes to three hours post-race, when your muscles are most receptive to taking up nutrients.
The target is a combination of carbohydrates and protein in roughly a 3:1 or 4:1 ratio. In practical terms, that’s about 1.2 to 1.5 grams of simple carbohydrates per kilogram of body weight, paired with 0.3 to 0.5 grams of protein per kilogram. For a 70 kg runner, that translates to approximately 85 to 105 grams of carbs and 20 to 35 grams of protein within that first post-race window. Chocolate milk has become a popular choice because it naturally hits close to that ratio, but a bagel with peanut butter plus a recovery shake works just as well. The key is getting something in quickly, even if your appetite is low. Your legs will thank you the next day.