Marathon Preparation: Understanding the Nutrition You Need to Run Your Best Race

Runner Nutrition

Nutrition and Your Race

Physio Logic’s clinical nutritionist, Michelle Miller, MSACN, discusses how to determine the correct amount of carbohydrates, proteins and fats you need to run your best race.

What do I eat?

By now you may be realizing that what you’re going to eat on a training day will probably differ from the day when you run 26.2 miles. This is absolutely correct.


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 and creates energy for muscle contractions up to 3x faster than fat.

There is a strong association between glycogen (storage form of glucose which 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 do you need?

Well, that depends on YOU!

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

To 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 sports nutritionist to tailor a plan specific to you!

Timing Your Carbohydrate Consumption

Before your event: At some point between 1-4 hours before your event, 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: 90g/hour (this will not be specific to your gender or size)

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!

Carbohydrate Choices

*The above picture notes what contributes to an average 15g of carbohydrate.



Now what’s the deal with protein? The RDA 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 recommends 1.2-2.0g/kg* for endurance athletes such as you!

This range is necessary to support metabolic adaptation, repair, remodeling, and for 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 following 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! 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.

Sources of Protein



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.

Endurance athletes that supplemented with Omega-3s experienced decreased muscle soreness, reduced swelling, and in some research decreased recovery time. Good animal sources are sardines, salmon, eggs, cod liver oil, tuna. 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!

Healthy Fat

To 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.

Take Aways

  • During this time of intense training, you must adequately fuel your body. Carbohydrates will make up the majority of your 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).

Preparing for the marathon or a long distance race? Schedule an appointment with our clinical nutritionist today. Fill out the form below to get started.