Marathon training demands more fuel than almost any other recreational pursuit. A typical training block lasting 16 to 20 weeks will progressively increase your calorie and carbohydrate needs, and what you eat on a daily basis matters just as much as what you consume during long runs. Getting nutrition right can mean the difference between finishing strong and hitting the wall at mile 20.
Daily Carbohydrate and Protein Targets
Carbohydrates are the primary fuel for endurance running. Your muscles store them as glycogen, and those stores get depleted during hard or long efforts. Most sports nutrition guidelines recommend endurance athletes consume between 5 and 10 grams of carbohydrates per kilogram of body weight per day, depending on training volume. On lighter days, you can sit at the lower end. On days with long runs or double sessions, aim higher. For a 70 kg (154 lb) runner, that translates to roughly 350 to 700 grams of carbohydrates daily.
Good daily carbohydrate sources include rice, oats, pasta, potatoes, bread, bananas, and sweet potatoes. These are calorie-dense and easy to prepare in bulk. You don’t need to eat “clean” all the time. Simple carbohydrates like white rice, bagels, and even pancakes digest quickly and are perfectly fine staples during heavy training weeks when your body needs fast-absorbing fuel.
Protein supports muscle repair and helps you recover between sessions. Aim for roughly 1.2 to 2.0 grams of protein per kilogram of body weight per day. That same 70 kg runner needs about 84 to 140 grams daily. Chicken, fish, eggs, Greek yogurt, beans, and tofu are all reliable options. Spreading protein intake across meals (rather than loading it all at dinner) improves absorption and keeps muscle repair going throughout the day.
What to Eat Before a Long Run
Your pre-run meal should be high in carbohydrates, moderate in protein, and low in fat and fiber. Eating two to three hours before you head out gives your body enough time to digest. A bowl of oatmeal with a banana, a bagel with a thin spread of peanut butter, or white rice with a small portion of chicken all work well. Drink 8 to 16 ounces of water in the one to two hours before you start.
The key is predictability. Your long run is not the time to experiment with a new breakfast. Find a meal that sits well in your stomach and stick with it week after week. By race day, it should feel automatic.
Fueling During Long Runs
For any run lasting longer than about 90 minutes, you need to take in carbohydrates while running. A single carbohydrate source (like glucose) can be absorbed at rates up to about 60 grams per hour. When you combine two types of sugar that use different absorption pathways, typically glucose and fructose, your gut can handle more. Current guidelines recommend 60 to 80 grams of carbohydrates per hour for runs in the two to three hour range, which is where most marathon efforts land. Research shows the greatest performance benefit occurs in that 60 to 80 gram window.
In practice, this means consuming a gel, a few chews, or a serving of sports drink every 20 to 30 minutes once you’re past the first 45 to 60 minutes of a run. Most commercial gels contain 20 to 30 grams of carbohydrates each. Some runners prefer real food on training runs: dates, honey packets, or gummy candies all provide fast sugar. What matters is the total carbohydrate amount per hour, not the specific product.
There’s growing evidence that even higher intake rates are beneficial. A study on elite mountain marathon runners found that those consuming 120 grams of carbohydrates per hour showed significantly less muscle damage and lower perceived exertion compared to runners taking in 60 or 90 grams per hour. However, tolerating that much sugar requires deliberate gut training, which brings us to an important point: your gut is trainable, but you have to practice.
Training Your Gut
Many runners skip fueling on training runs, then wonder why gels make them nauseous on race day. Your intestines adapt to processing carbohydrates during exercise, but only if you practice regularly. Start with small amounts (30 grams per hour) early in your training block and gradually increase. The runners in the 120 g/h study had practiced consuming up to 90 grams per hour at least twice a week for four weeks beforehand. By the time you reach your peak long runs, your fueling strategy should mirror exactly what you plan to do on race day.
Carb-Loading Before the Marathon
Carb-loading is not just “eating extra pasta the night before.” Done properly, it’s a 36 to 48 hour process where you increase your carbohydrate intake to 10 to 12 grams per kilogram of body weight per day. For a 70 kg runner, that’s 700 to 840 grams of carbohydrates daily for a day and a half to two days before the race. This saturates your muscle glycogen stores and gives you a larger fuel tank on race morning.
This is a lot of food, and it takes planning. You’ll want to rely on low-fiber, carbohydrate-dense options: white rice, white bread, pasta, pretzels, juice, jam, sports drinks, and pancakes. Fiber takes up stomach space without adding usable fuel, and it can cause GI issues on race morning. Many runners are surprised by the volume of food required, so practice a carb-loading window before one of your last long training runs to see how your body responds.
Recovery Nutrition After Hard Efforts
What you eat in the 30 minutes after a long run or hard workout sets the stage for how you feel at your next session. The goal is to replenish glycogen stores and kickstart muscle repair. The most effective approach is a combination of carbohydrates and protein in roughly a 3:1 or 4:1 ratio. That translates to about 1.2 to 1.5 grams of simple carbohydrates per kilogram of body weight, plus 0.3 to 0.5 grams of protein per kilogram.
For a 70 kg runner, that’s roughly 85 to 105 grams of carbohydrates and 20 to 35 grams of protein within that first half hour. A large glass of chocolate milk, a smoothie with banana and protein powder, or a bowl of cereal with milk all hit close to these targets. Follow up with a full meal within the next two hours. During peak training weeks when you’re running six days a week, nailing this recovery window consistently makes a noticeable difference in how fresh your legs feel.
Hydration and Sodium
Water alone isn’t enough for runs lasting more than two hours. You lose sodium in your sweat, and failing to replace it can lead to hyponatremia, a dangerous drop in blood sodium levels. The American College of Sports Medicine recommends 300 to 600 milligrams of sodium per hour during prolonged exercise. Most sports drinks contain some sodium, but many runners find they need additional electrolyte tablets or capsules to hit that range, especially in hot weather.
Sweat rates vary dramatically between individuals. A useful test is to weigh yourself before and after a long run (without drinking during the run) to estimate how much fluid you lose per hour. Aim to replace roughly 80% of that loss during your actual runs. Overdrinking is just as problematic as underdrinking. Sipping consistently rather than gulping large amounts at aid stations reduces the risk of stomach sloshing and nausea.
Avoiding Stomach Problems
Gut issues during running are extremely common. The culprit is often a class of short-chain carbohydrates found in everyday healthy foods. These include fructans (in garlic, onion, wheat, and rye), lactose (in milk and yogurt), excess fructose (in apples, honey, and some sports products), and sugar alcohols like sorbitol and mannitol (in sugar-free gums and some fruits). During intense exercise, when blood flow is diverted away from your digestive system, these compounds draw extra water into the intestines and ferment rapidly, causing bloating, cramping, and diarrhea.
The most effective strategy is to reduce your intake of these fermentable carbohydrates in the 24 to 48 hours before a long run or race. This doesn’t mean eliminating them from your regular diet. It means being strategic in the day or two before hard efforts. Swap garlic and onion-heavy meals for simpler seasoning. Choose white rice over wheat-based foods. Skip the apple and reach for a banana. Use lactose-free milk if dairy bothers you. Many elite runners follow this approach instinctively without knowing the science behind it.
High-fat and high-fiber foods are the other common offenders before runs. A large salad or a meal heavy in nuts and seeds the night before a long run can sit in your gut the next morning. Keep your pre-run meals boring and well-tested. Save the adventurous eating for rest days.
Putting It All Together Week by Week
Early in your training block, when weekly mileage is lower, focus on building consistent eating habits: regular meals, adequate protein at each one, and enough total carbohydrates to support your runs. Practice your mid-run fueling strategy even on moderate long runs of 90 minutes, using it as a chance to test products and train your gut.
As mileage increases in the middle weeks, your calorie needs will climb noticeably. Many runners undereat during this phase, which leads to fatigue, poor recovery, and increased injury risk. If you’re losing weight unintentionally during a training block, you need more food. Adding an extra snack between meals or increasing portion sizes at dinner are simple fixes.
In the final two to three weeks, as you taper your mileage, your carbohydrate needs on easy days will drop. But in the 36 to 48 hours before race day, you’ll shift into carb-loading mode. By this point, every element of your nutrition plan, from your pre-run breakfast to your gel schedule to your recovery shake, should be fully rehearsed. Race day is about execution, not experimentation.