A Runner’s Diet: Marathon Preparation & Understanding the Nutrition for Runners to Run Their Best Race

Clinically reviewed by Michelle Miller, MSACN

Nutrition for Runners and Your Race

How to determine the proper diet for runners; the correct amount of carbohydrates, proteins, and fats you need to run your best race.

With the return of in-person races, many are lacing up their sneakers in anticipation of a busy race season. As your training and weekly mileage increases, it is important to think about how nutrition factors into your marathon plan. A runner’s nutrition plays an integral role in our ability to successfully complete–and recover from– those longer runs. Whether it’s your first marathon or you have several under your belt, here’s what all runners should know about a runner’s diet plan as they prepare for the starting line.

What do I eat?

It should come as no surprise that your energy needs will be higher due to increases in physical activity. Hunger is one of the most common side effects mentioned by my clients. Focusing on the composition of macronutrients — or carbohydrates, proteins, and fats– in a runner’s diet plan is key. Carbohydrates, Proteins, and Fats each have a different function in the body. Understanding these differences can support muscle recovery and help runners, and all athletes, achieve their goals. Let’s break them down:


Carbohydrates are broken down into glucose and are stored in the body as glycogen. Muscle glycogen is used the most rapidly during the first stages of exercise. And you guessed it, you’re going to need to make sure you’ve got adequate stock. This is the only nutrient that can be used for anaerobic energy production (used for short, intense activities like sprinting and heavy weight lifting) and creates energy for muscle contractions up to 3x faster than fat.

There is a strong association between glycogen (the storage form of glucose that is derived from carbohydrates) and fatigue.

So what is the role of carbohydrates during activity?

Carbs power contractile proteins of muscle and fuel the brain and the central nervous system. It is also important to note that carbs spare protein by minimizing gluconeogenesis (which is when proteins are oxidized for fuel…not ideal).

So how much carbohydrates are optimal in a runner’s diet plan?

That depends on YOU!

We assess carbohydrate needs based on grams per kg of body weight. Specific needs vary with the type of exercise, intensity, duration, and gender. The goal is to match glycogen stores and blood glucose to fuel demands of exercise.

Note: kg = lbs/2.2

Training day carbs: 3-5g/kg for low intensity (shorter training days)/ 8-12g/kg for very high intensity.

Ex. If you are 150 lbs, you are roughly 68 kg (150 lbs divided by 2.2). If it is a light training day you may consider 4g/kg. So 4g/68kg= 272g of carbohydrates.*

*Work with a nutritionist to tailor a runner’s diet plan specific to you!

Timing Your Carbohydrate Consumption

    • Before your event: At some point between 1-4 hours before your event, runners should top off stores with 4g/kg of carbohydrates.

Ex. If you are 150 lbs, you are roughly 68 kg (150 lbs divided by 2.2). If this is your event day, you may consider 4g/kg. So 4g/68kg= 272g of carbohydrates before your race.

  • During event: 60- 90g/hour
  • After: Every hour, for 4 hours following your race, be sure to get 1-1.2g/kg of carbohydrates.

Your body NEEDS carbs; this is not the time for a low-carb diet!

Nutritional Macros: Carbohydrate options for a runner's diet while preparing for a marathon or long-distance run.


Now, what’s the deal with protein? The RDA (Recommended Dietary Allowance) recommends 0.8g/kg of protein per day for healthy individuals. However, studies have shown that protein requirements are elevated for athletes. The ADA/ACSM (American Diabetes Association/American College of Sports Medicine) recommends 1.2-2.0g/kg* for endurance athletes, such as runners!

This range is necessary to support metabolic adaptation, repair, remodeling, and protein recovery. The ADA/ACSM recommendations encompass most training regimes. However, requirements can change based on “trained” status (experienced athletes requiring less), exercise intensity, carbohydrate availability, and total energy intake.

This requirement can be met by diet alone! Seek to distribute high-quality protein throughout the day and/ or follow key training sessions to the tune of 0.25-0.3g/kg or roughly 15-25g. Research shows increases in strength and muscle mass with immediate post-exercise ingestion of protein.

Ex. If you are 150 lbs, you are roughly 68 kg (150 lbs divided by 2.2). Total protein needs throughout the day are between 81.6g-136g. Spread throughout the day and following key exercise bouts. That translates into = 20.4g to 27.2g spread over 4 or 5 meals.

It’s important to consume high-quality dietary proteins for a runner’s diet or any macronutrient-based nutrition plan for athletes! According to the ADA/ ACSM, high-quality protein sources include milk-based proteins due to their high leucine content and the digestion and absorption kinetics of branched-chain amino acids in fluid-based dairy foods. If milk-based products don’t float your boat, below is a list of other high-quality protein sources.

Nutritional Macros: Protein options for a runner's diet while preparing for a marathon or long-distance run.


Fat intake depends on exercise intensity, duration, and carbohydrate stores/intake during exercise. Higher carbohydrate and protein intake typically means lower fat intake, which is what you’re going for.

However, severe restriction of fat intake is also not recommended. Generally, we should be looking for fat to make up 20-35% of total caloric intake. To achieve proper fat intake, athletes should look at roughly 1g/kg daily.

Omega 3 Fatty Acids: Research has shown that Omega-3 Fatty Acids, found in both plants and fish, are beneficial to endurance athletes. Omega-3s are found in cell membranes and are important to immune function and modulating inflammation and recovery.

Research shows that endurance athletes such as runners that supplement with Omega-3s experience decreased muscle soreness, reduced swelling, and in some studies, decreased recovery time. Omega-3 rich animal sources include sardines, mackerel, anchovies, salmon, herring, grass-fed eggs, and cod liver oil. Aim for between 1000mg-2000mg/ day! One serving of fatty fish every other day will get you to that goal as will the appropriate intake of plant-based Omega-3s or a high-quality fish oil supplement!

Nutritional Macros: Fat options and Omega 3 Fatty Acids for a runner's diet while preparing for a marathon or long-distance run.

Note: Krill oil has been shown to be especially effective at lower doses than fish oil although more research is needed to support these findings.


  • During this time of intense training, you must adequately fuel your body. Carbohydrates will make up the majority of a runner’s diet, followed by protein, and then fat.
  • Be mindful of the different intake amounts of carbohydrate/protein/fat depending on your energy expenditure (light training days vs. longer race day marathon).

Hey, all you runners out there! Are you preparing for a marathon or a long-distance race? Schedule an appointment with our Integrative Nutrition department today. Give us a call or fill out the form below to get started…

Contact Us