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Marathon Nutrition: The How and Why of Supplementation

by Connie Hutchins, PT, DPT

 

You’ve put countless hours into training for the upcoming marathon and you’re getting close to race day! You’re probably wondering how you should prepare for the demands of race day, particularly with what to eat and when. You’ve likely heard about carbohydrate loading, gels, sports drinks, and frequently drinking water. While these are all important to consider, you may be wondering how to best incorporate these factors into your preparation and race day.

 

What about carb loading?

Carbohydrates are largely responsible for fueling your body during a marathon so it’s important to optimize your carbohydrate sources during the race. Your body stores carbohydrates, particularly glucose, in the form of glycogen (glucose chain) within your muscles and liver. As you start to exercise your body breaks down the glycogen into glucose which your body uses to create energy within your cells. Simply put, increased glycogen stores equates to increased energy stores. Your normal glycogen stores last for about 90 minutes of endurance exercise, which is why it’s beneficial to increase your stores to provide energy throughout the marathon. Carbohydrate loading, eating meals primarily composed of carbohydrates the day before the race, has been found to increase the stores of glycogen within your muscles.

 

How much carbohydrates do you need to eat before the race?

The recommendation for carbohydrate loading includes consuming 6-10g/kg body mass/day (2.7-4.5g/lb body mass/day) with the higher values being used in most studies. Some carbohydrate loading programs start sooner, at 3 days prior to the event, but studies show similar results with a 1 day carbohydrate loading program. In regards to eating a meal before the marathon, it is recommended that a high carbohydrate meal be eaten 3-4 hours before the start of the race.

 

What about during the race? Where do gels and sports drinks fit in?

Gels have a combination of carbohydrates (glucose & fructose) and sodium that specifically helps to transport these nutrients optimally from your stomach into your blood stream. Sports drinks have also been developed with this concept in mind. Some researchers attribute GI distress to accumulation of carbohydrates in the GI tract and these sources of supplementation are made to be easy to digest to avoid GI distress and keep your carbohydrate and electrolyte levels in check.

 

How often and how much gel should be used?

Studies range from showing beneficial effects of 40-75 grams/hour of carbohydrate supplementation, which equates to 2-4 Gu or Clif Shot gel packets every hour. Each runner will absorb and utilize carbohydrates and fluids slightly differently, accounting for the range and variability in supplementation recommendations. During the marathon there are 22 aid stations which provide water and Gatorade Endurance Formula drinks. The water provides the fluid intake to compliment your gels and the Gatorade contains a balance of fluid, carbohydrates and electrolytes. There will also be two tents providing Clif Shot gels (at Mile 12 & Mile 19). Training is the perfect time to test the general recommendation and make adjustments to find your own timing and balance of carbohydrate and fluid intake.

 

How much water should I drink and when?

Regarding water intake, 5-7mL/kg body weight (5-7mL/2.3kg body weight) of water is recommended 4 hours before the event. If you’re producing dark or highly concentrated urine, add another 3-5mL/kg body weight, 2 hours before the event. During the event, the American College of Sports Medicine recommends 0.4-0.8 L/hr (1.7-3.4 cups/hr) of fluid intake. It’s important that your fluid intake be spread throughout the race in order to avoid large intakes of fluid producing hyponatraemia, a dilution in the amount of sodium in the blood stream. This is why aid stations are laid out very frequently throughout the course.

 

Be aware that you may need to adjust your supplementation depending on weather. On hotter days, you may need to increase your fluid and electrolyte intake if you’re losing more fluid in sweat.

 

Congratulations on all the hard work that you’ve put into training. Enjoy the marathon!

Summary of Recommendations:

Carbohydrate loading: 6-10g/kg body mass/day (2.7-4.5g/lb body mass/day) the day before the race.

 

Gels + Water:

Gels: 40-75 grams/hour of carbohydrate = 2-4 Gu or Clif Shot gel packets every hour.

Water: 5-7mL/kg body weight (5-7mL/2.3kg body weight) of water, 4 hours before the event. If urine is dark/concentrated add 3-5mL/kg body weight, 2 hours before the event. During the marathon drink 0.4-0.8 L/hr (1.7-3.4 cups/hr).

 

Gatorade: 12 oz/hr (1.5 cups/hr).