The Runner’s Ultimate Guide to Marathon Training Nutrition

An expert dietitian dishes on everything you need to know about fueling for optimal training and race performance


As if logging many, many miles week after week weren’t enough to handle, there are several challenging obstacles involved with training for a marathon, one of the most difficult being maintaining a smart approach to your nutrition and eating habits.

Keeping a focus on balanced, nutrient-dense meals isn’t necessarily easy to do in the first place, so when you throw the increased, almost ravenous appetite that comes along with marathon training into the mix it can become quite hard to keep up, and especially hard to choose the nutritious foods that will benefit your body best.

There’s a lot that goes into fueling right while training for a marathon, so we recruited Alexandra Miller, R.D.N., L.D.N., corporate dietitian at Medifast, Inc., to share her expert advice on all of the different elements that make up a smart strategy for marathon training nutrition.

David Acosta Allely/ Shutterstock

(Photo Credit:David Acosta Allely /

What Not to Do
Miller said runners should make a point to avoid two common mistakes: not hydrating properly and not consuming a proper balance of carbs and protein.

Hydrating Properly: “Water helps maintain homeostasis in the body and allows for the transport of nutrients to cells and the removal and excretion of waste products of metabolism,” Miller explained. “Dehydration can lead to early fatigue, cardiovascular stress, increased risk of heat illness and decreased performance in runners.”

Her advice? Always hydrate throughout the day and especially within one hour before any workout sessions. Additionally,  sweat losses should be replaced by drinking fluids regularly during exercise. After a workout, be sure to rehydrate to replace weight lost as fluid.

Tip: "On race day, have two to three glasses of water up to two hours before the race begins to allow time for excretion," Miller said. "Then drink up to one additional cup, or as your body tolerates."


Carb-Protein Balance: “Carbohydrates are needed to fuel the body both physically and mentally throughout training and the race,” Miller said. “Protein is needed to help muscles recover and repair properly. Therefore, meals and snacks should contain a combination of both.”

She suggests: For healthy marathon runners, aim to consume approximately three grams of carbohydrates and 0.6 to 0.7 grams of protein per pound of body weight for an entire day. Spread the total amounts of carbohydrate and protein evenly throughout the day, being sure to include some of both with each meal and snack.

Additionally, Miller mentioned that many runners struggle with being sensible about food choices.

“If carbohydrate loading, consume a variety of foods that your body tolerates well,” she explained. “Don’t, for example, consume all your carbohydrates from fruit — this often leads to diarrhea. And avoid consuming large quantities of refined grains, like white bread, as this may lead to constipation.”

She also advised that runners should maintain awareness about their fat intake.

“Be careful not to ‘fat load,’” Miller said. “Fat is not as easily digested and may cause gastrointestinal distress while exercising. This, of course, can vary from person to person.”

Related: A Balanced Diet For Athletes: Carbs, Fats, Protein

Maintaining a Smart Nutrition Strategy Throughout Training
Eating well all throughout your training cycle — not just as race day draws closer or when the big day finally arrives — is important for optimal performance.

“Good nutrition ensures your body is properly fueled for top performance and nourished for good health,” Miller said. “Inadequate nutrition can lead to fatigue, muscle cramps, poor performance and injury.”

What’s her advice for sticking with a good diet all through training?

“Find a plan that works for you,” Miller explained. “Consider your individual nutrient needs, food preferences and tolerances, schedule, and ability/willingness to cook and prepare meals. Take time to think through any barriers that may impact your ability to follow your plan each week, such as a busy schedule, inability to cook, etc., and brainstorm solutions. You may want to enlist the support of some friends or family to help keep you motivated and/or try self-monitoring your progress with an online food and activity tracker.”

Miller said two of the most common obstacles include busy and unpredictable schedules. Here’s her advice for dealing with each.


Busy Schedule: Find ways to make eating right convenient and healthy, such as picking a day to batch-cook — cut up vegetables and pack them into re-sealable baggies so they are ready to grab and go; prep a large salad to last throughout the week; pre-portion nuts and dried fruits in little baggies to ensure calorie control; bake or grill extra chicken or other sources of protein a couple of days out to save time during the week — and slow-cook so you can make large meals with extras to have as leftovers.

Related: Dietitian-Approved Tips for Healthy Meal Planning Made Easy

Unpredictable Schedule: Be sure to grocery shop so that you are well-stocked with healthy options —  quick-cooking, pre-portioned packs of whole grains, such as quinoa, farro or brown rice; yogurt cups; low-fat cheese sticks; fresh fruit, like grapes, bananas and apples; low-sodium beans; tuna, salmon, or chicken canned and packed in water; plain, frozen veggies; etc. Also, keep a healthy supply of foods available wherever you go: at home, work or in your gym bag.

Eating Before and After Workouts
When it comes to properly fueling for your workouts, Miller suggests a light carb-protein balanced meal about three to four hours beforehand.

This might include: peanut butter on whole wheat bread and a Medifast Shake; oatmeal with almonds, skim milk and a banana; low-fat cottage cheese with fresh fruit and granola; turkey and Swiss on whole grain bread with a piece of fruit and yogurt.

“Thirty to sixty minutes before your run, have a small carbohydrate-rich snack, like a piece of fruit or a sports drink,” Miller said. “And begin nutrition recovery with a snack or meal within 15 to 60 minutes following your workout.”


Foods to Focus On

Fruits and Vegetables: “They are a rich source of the vitamins and minerals needed to keep your body healthy,” Miller said. “This includes, but is not limited to, strong bones, muscles that contract properly and good vision. Fruits and vegetables also promote a healthy immune, digestive, and cardiovascular system. They are also rich in phytonutrients, like antioxidants which help deactivate free radicals in the body. Aim to have at least one fruit and vegetable with every meal.”

• Lean Protein: “It’s needed for muscle recovery and repair,” Miller explained. “Aim for 10 to 20 grams per snack and 20 to 30 grams per meal. Lean protein sources include boneless skinless chicken breast; fish/shellfish; lean ground meats (>90% lean); egg whites; lean cuts of beef (i.e. roast — chuck, rib, rump); round, sirloin, steak (flank, porterhouse, tenderloin, etc.); white meat turkey; pork chops trimmed of fat; beans and lentils.


• Nutrient-Rich Carbohydrates: “These include whole grains and starchy vegetables, which offer essential vitamins, minerals and dietary fiber,” Miller said. “Include whole grains, like amaranth, popcorn, quinoa, brown rice, and oatmeal, and starchy vegetables, like sweet potatoes, winter squash and corn in your daily regimen.”

The Value of Carb-Loading
As Miller explained, carbohydrates are the bodies primary source of fuel, and you’ll be using a lot of it, which is why marathoners are advised to increase their carb intake during training.  

“Carbohydrate loading should be practiced prior to the event to ensure the body tolerates the food choices and corresponding quantities well,” Miller said. “In fact, carbohydrate loading should be practiced daily throughout the marathon training period."

This, Miller explained, not only helps your body adapt to the process but also ensures there will be no dietary “surprises” on the day of or before the event.

“Carbohydrate loading throughout the training period allows your digestive system, lungs and muscles to become accustomed to the nutrient intake. It also helps prevents gastrointestinal distress, like bloating, diarrhea and constipation. “


How to Carb-Load
“The exact timing of the meals and quantity of food eaten the day before a race will vary from person to person,” Miller said. “Do what your body best tolerates.” This means it’s necessary to test out what works best for you with a trial and error method well before race day.

The Day Before the Race: “You want to build your energy stores yet avoid overfeeding yourself,” Miller said. “Learning the right balance and timing of your meals takes practice, which is why it is important to include proper nutrition throughout the training period.”

Mainly, though, carb-loading for endurance athletes, Miller advised, should include about three to five grams of carbohydrates per pound of body weight per day to prevent chronic glycogen (the stored form of carbohydrates in the body) depletion.

“Of course, adequate protein and healthy fats should also be included as part of the diet,” Miller added. “Consuming carbohydrates in excess of what is recommended will offer no further benefit as the body can only digest and store so much at one time. Gastrointestinal distress, such as bloating, can also result and negatively impact training efforts.”

She suggested using an online food-tracker to develop a meal plan that works well for your own personal needs.

“Many online food trackers will help estimate your calorie and nutrient needs and allow you to evaluate your daily food intake to ensure you are meeting those requirements,” Miller said.

Additional Considerations
Miller pointed out three more important factors all runners should keep in mind during marathon training.

Increased Appetite: “Long bouts of exercise will naturally increase your appetite,” she explained. “If you are looking to manage your weight, be sure to keep track of the calories you are consuming. In order to maintain your weight, the calories you consume should equal the calories you burn in a day. While exercise can help prevent weight gain, what you eat is as equally important — in fact, it’s more important if you are trying to lose weight.”

Eat Breakfast on Race Day: “Eat breakfast the day of your event,” Miller said. “It can be tempting to skip when the pre-race jitters set in. Eating breakfast will prevent hunger and help your body maintain stable blood glucose levels, both of which are needed to help prevent muscle and mental fatigue. Being mentally prepared is just as important as being physically prepared and eating right the day of the race will ensure you are ready for both.”

Alcohol Intake: ​"An occasional glass of wine or beer will not mean life or death. However, alcohol can have a negative impact on your training and performance," Miller said. "If you do choose to drink, do so sparingly and in moderation. Do not skip meals to make up for calories consumed from alcohol. Have a glass of water in between each adult beverage you consume and never have alcohol on an empty stomach."

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