Whether you’re approaching race day or just beginning your training cycle, understanding the fundamentals of sports nutrition is essential for building an effective marathon training diet.
Today, nutrition is widely recognized as being just as important as the training itself. For endurance athletes like marathon runners, proper fueling goes far beyond relying on sports drinks alone—it requires eating the right foods, in the right amounts, to support both performance and recovery.
That’s why we’ve outlined 10 key rules for marathon training nutrition to help you build a fueling strategy that works. While designed with marathon runners in mind, these principles apply just as well to athletes training for a half-marathon or ultramarathon.
By following these guidelines, you’ll be able to fuel your runs more effectively, recover faster, and show up on race day in the best possible condition.
#1: Understand your metabolic needs
Marathon training dramatically increases your energy demands. Runners burn roughly 90–110 calories per mile, meaning a 15-mile long run can easily cost around 1,500 calories. To recover properly and continue adapting to training, those calories need to be replaced.
If you consistently train in a calorie deficit, your body may begin breaking down muscle tissue for energy. This can slow recovery, weaken performance, and increase injury risk.
From a coaching perspective, one of the most important principles of marathon nutrition is simple: make sure you’re eating enough to support your training load.
A helpful first step is calculating your Basal Metabolic Rate (BMR)—the number of calories your body burns at rest just to maintain essential functions like breathing and circulation. BMR typically accounts for 60–70% of your total daily energy expenditure, making it a critical starting point for determining how much you should eat each day.
Once you know your BMR, you can estimate your total daily calorie needs by factoring in daily activity and the calories burned during training.
If you’re not sure how to calculate it, check out our full guide here:
https://marathonhandbook.com/basal-metabolic-rate/
Remember that calorie needs will fluctuate throughout the week—long run and workout days require significantly more fuel than easy runs and rest days. Adjusting your intake to match your training load will help you recover faster, maintain muscle mass, and perform at your best.
#2: Keep Macros in Balance
Carbohydrates
For marathon runners, carbohydrates are the primary fuel source.
During running, your muscles rely heavily on glycogen, the stored form of carbohydrate in your muscles and liver, to power sustained effort. Replenishing those glycogen stores is essential for maintaining performance and recovering between workouts.
Because of this, carbohydrates should make up the largest portion of your daily calorie intake, especially during periods of higher mileage and harder workouts.
During intense training phases—when your mileage, long runs, and workouts increase—most runners should aim for roughly 5–7 grams of carbohydrates per kilogram of body weight per day. For a 120-lb (54 kg) runner, that works out to about 270–380 grams of carbs per day.
On lighter training days or rest days, carbohydrate needs can drop slightly to around 3–5 grams per kilogram of body weight, since the body is burning less glycogen.
Focus primarily on complex carbohydrate sources that provide sustained energy and nutrients, such as:
- Whole grains (oats, brown rice, quinoa)
- Potatoes and sweet potatoes
- Beans and lentils
- Fruits and vegetables
- Whole-grain bread and pasta
These foods help keep your energy levels stable while also providing fiber, vitamins, and minerals that support overall health and recovery during marathon training.
Protein
Protein is the next most important macronutrient for replenishing muscle breakdown. Adequate protein intake is necessary to help your muscles recover.
On training days, aim for 0.7 – 1.0g of protein per pound of body weight, while on non-training days, aim for 0.5 – 0.7g per pound of body weight.
Fat
Fat is the final macronutrient and is needed to support vitamin storage and hormone production, but should be kept at around 0.5g per pound of bodyweight on training and non-training days.
While many people associate fat with something to avoid as part of any diet, it is undeniably important when training for a marathon. You can cook with foods high in healthy, unsaturated fats, such as olive oil, nuts, seeds, and fish, to get the fats you need when training for a marathon and keep your diet healthy.
Related: Running Rules: The 13 Unspoken Rules + Proper Running Etiquette
#3: Fuel Before And After Your runs
Long endurance runs can significantly deplete your body’s glycogen (carbohydrate) stores, which is why fueling around your workouts is essential for maintaining performance and recovery.
Before running—especially for longer or harder sessions—eat an easily digestible carbohydrate snack about 60 minutes beforehand. This helps top up your available energy and prevents starting a run on empty. Good options include:
- A banana or other fruit
- A sports gel
- A slice of toast with honey or jam
- A small energy bar
After your run, the goal is to replenish glycogen and support muscle repair. Try to eat within 30–60 minutes of finishing your workout, when your body is most efficient at absorbing nutrients.
A good rule of thumb is to aim for roughly a 3–4:1 ratio of carbohydrates to protein in your post-run meal or snack. This combination helps restore glycogen stores while providing the amino acids needed for muscle recovery.
Examples include:
- Greek yogurt with fruit and granola
- A smoothie with banana, berries, and protein powder
- Rice or potatoes with lean protein
- Chocolate milk with a carb-rich snack
Consistently fueling before and after your runs is one of the most effective ways to stay energized between workouts and support the demands of marathon training.
- Related: Intermittent Fasting And Running
#4: Eat clean foods
Whole foods are the easiest for the body to digest and pull nutrients from.
Eating the cleanest sources of food available to you will ease digestion and increase nutrient absorption, aiding the recovery process during your marathon training.
When shopping for foods to eat during your marathon training, go with organic, natural, and as close to whole foods as you can, and try to avoid processed foods.
#5: Minimize added sugars
Most marathon runners rely on sports drinks, energy gels, and other quick fuels at some point during training. These products are designed to provide simple sugars, which are rapidly absorbed and converted into energy.
During long runs or races, this is exactly what you want—quick, easily digestible carbohydrates that can keep your muscles fueled and help prevent hitting the wall.
Where runners sometimes run into trouble is relying on these products too heavily outside of training. While simple sugars are useful during exercise, the majority of your daily nutrition should come from whole foods and complex carbohydrates that provide sustained energy along with essential nutrients.
A good rule of thumb is to separate your fueling strategy into two categories:
- During runs: prioritize simple carbohydrates like gels, chews, or sports drinks for quick energy.
- During daily meals, focus on complex-carbohydrate sources such as whole grains, potatoes, fruit, beans, and vegetables.
In short, simple sugars have their place—but mainly during your runs. Save the bulk of your carbohydrate intake for nutrient-dense foods that support recovery, overall health, and consistent training.
#6: Keep snacks on hand
As we’ve mentioned before, marathon runners burn calories like crazy.
To keep calorie count high, especially on training days, keep pre-packed healthy snacks with you wherever you go.
These snacks should fall under all the rules we’ve laid out thus far. They need to be primarily carbs, low in added sugars, a clean source of energy, and perhaps most importantly, something you enjoy.
Packing snacks before the day starts gives you a plan to fuel your training and a reason to avoid candy bars.
#7: Find the Right Foods
Everyone’s digestive system responds differently to foods and sports fuels. If a particular gel upsets your stomach or a certain food doesn’t sit well during a run, it’s best to avoid it.
There’s no universal rule that marathon runners must eat specific foods like potatoes, use a certain brand of gummies, or rely on nut butters for fuel. What works perfectly for one runner may not work for another.
The key is to experiment during training—not on race day—to find the foods and fuels your body tolerates well. Once you discover what you can digest comfortably and what keeps your energy steady, stick with it and make it part of your regular fueling routine.
8. Hydrate, Hydrate, Hydrate
Hydration is critical for muscle health (preventing cramps), body temperature regulation, and vitamin and mineral absorption.
When you’re out on the road putting in your miles, your body loses considerable water through sweat; the average person sweats between 0.8 and 1.4 liters per hour of intense exercise.
Taking small sips of water every 15-20 mins during a run will go a long way to replace what is lost.
Electrolyte drinks can also be useful for replenishing lost salts and other minerals during dehydration.
#9: Supplement Where Needed
A well-balanced diet should always be the foundation of your marathon training nutrition. However, certain supplements can help fill nutritional gaps or support recovery, particularly during periods of heavy mileage or intense training.
For example, omega-3 fatty acids (fish oil) may help reduce inflammation and support joint health, while ginger has been shown in some studies to help with muscle soreness and recovery after hard workouts. These can be useful additions if you’re dealing with frequent soreness or high training loads.
Some runners also use protein supplements or essential amino acids (EAAs/BCAAs) to support muscle repair, especially if they struggle to meet their daily protein needs through food alone. While whole-food protein sources are ideal, a simple post-run protein shake can be a convenient option during busy training weeks.
There are also a few nutrients endurance athletes commonly monitor:
- Vitamin D: Important for bone health, immune function, and muscle function—especially for runners training indoors or in low-sunlight climates.
- Iron: Critical for oxygen transport and endurance performance. Runners—particularly women and high-mileage athletes—may be at risk of low iron levels.
- Calcium: Supports bone strength and helps reduce the risk of stress fractures.
- Magnesium: May help with muscle function, recovery, and sleep quality.
- Electrolytes (sodium, potassium, magnesium): Useful for replacing minerals lost through sweat during long runs.
Some runners also experiment with performance-focused supplements, such as caffeine (an evidence-backed ergogenic aid) or nitrate-rich foods like beetroot juice, which may improve endurance efficiency in certain athletes.
That said, supplements should be viewed as a complement to a solid nutrition plan—not a replacement for it. Whole foods provide a wide range of nutrients that supplements alone cannot replicate.
Most importantly, always consult with your healthcare provider or a qualified sports nutrition professional before starting any new supplement, especially if you have underlying health conditions, take medications, or suspect deficiencies such as low iron or vitamin D.
Proper testing and professional guidance can help ensure you’re supplementing safely and effectively.
#10: Don’t Try Anything New on Race Day
All these rules for a marathon training diet should be practiced during training. Race day is not the day to try something new.
Practice fueling, hydrating, and experimenting with energy gels and energy sources prior to the day of your marathon in order to get the most out of your race-day nutrition.
Marathon training nutrition and half marathon training nutrition don’t have to be difficult, but they should be taken seriously.
Following these 10 rules for eating during your marathon training plan will increase your energy on the road, keep your muscles primed for training days, ensure you are getting the calories and nutrients your body needs, and prepare you for race day.
bonus tip! :
#11: Follow a Meal Plan
Alright, I know we only said 10 rules, but the 11th – and possibly most important rule – is to have a Marathon Training Meal Plan in place.
Where to start?
Check out our completely free, downloadable marathon training meal plans.
We include:
- Sample 1-week marathon meal plan
- Sample ‘week before your marathon‘ meal plan
- Sample vegetarian 1-week marathon meal plan
- Sample vegetarian ‘week before your marathon’ meal plan
Check out our marathon training meal plans:
