Fueling for Peak Marathon Performance

Kim Mueller, M.S., R.D.
Competitor Magazine

Have you ever started a long run feeling amazing only to suffer tremendously towards the end of the workout? Perhaps your muscles felt like they were experiencing a migraine headache and every slight incline in the road felt like you were climbing Mount Everest. Even those typical downhill blessings felt horrible, almost as if someone were hammering your legs into the ground or stabbing your muscles with a blade.

Most runners have had at least one or two less-than-desirable long training runs throughout a marathon-training program. Fortunately, these "bad" days can be minimized through careful planning of dietary and fluid needs during longer training bouts. Below, I provide three essential fueling tips to help you on your way to peak marathon performance.

1. Load Your Fuel Tank Before Starting.

While runners can get away with not eating before moderate-intensity training bouts lasting less than an hour, performance tends to decline if food is neglected prior to exercise lasting longer than an hour--especially if the exercise occurs in the morning after a prolonged fasting state.

The food consumed prior to longer training bouts will restock liver glycogen stores (helping to stabilize energy levels during the initial stages of training) and increase fuel efficiency due to sparing of muscle glycogen. Runners who fail to fuel prior to long training will "bonk" and start depleting their muscle glycogen stores prematurely and most likely fall prone to the performance declining "wall."

As a general rule, for every hour prior to exercise, athletes should consume about two calories per pound of lean body weight, aiming at one gram of protein for every four grams of low-to-moderate glycemic-index carbohydrate.

For example, a 150-pound runner with a body composition of 15 percent (85 percent or 127.5 pounds of lean tissue), requires approximately 255 calories one hour prior to training, which would be equivalent to consuming an energy bar.

In addition, athletes should drink approximately 16-24 ounces of fluid in the one to two hours prior to starting to help aid in digestion. A salty beverage (e.g., sports drink) provides additional anti-cramping benefits for the marathoner. High-glycemic carbohydrates, which include most sport drinks, are appropriate for consumption within an hour prior to starting, but should not make up the majority of a meal eaten more than one hour prior to starting a workout.

Foods rich in fiber (>5 grams per serving), protein (>15 grams) and fat (>3 grams per serving) should be avoided in the pre-workout meal since these nutrients cause a diversion of blood, oxygen and water flow to the stomach to aid in digestion, thereby leading to a "dead-legged" feeling and a frantic search for a restroom.

Runners should try several different pre-workout meals during training to determine which helps them perform and feel their best. New foods should NOT be experimented prior to important races. My personal pre-race fueling regimen includes a Pure Fit Bar (www.purefit.com), coupled with eight ounces of 100 percent fruit juice, two hours prior to race start. Then I'll sip on 16 ounces of my customized sports drink (www.infinitnutrition.com) as a means to salt load and top off my glycogen tank before I take off running.

2. An Hour Into Training, Start Refueling Your Tank.

The goal on longer training runs, as well as marathon race day, is to preserve glycogen and tap into the ever-so-abundant amount of fat stores within the body. Remember that "fats burn in a carbohydrate flame."

Picture carbohydrates as kindling under a fire and fat as a big log. Without an adequate amount of kindling or carbohydrate, the body fails to burn fat and starts to deplete precious muscle glycogen stores until the fuel tank is empty, leading to that ugly "wall" and mind-boggling "bonking" that generally occurs between mile 18 and 20 in a marathon (and even sooner if pre-race fueling is inadequate).

In order to prevent "the wall" and "bonking" and increase fat burning capabilities, it's essential to start refueling the body's fuel tank after about 60-90 minutes of moderate-to-high intensity exercise.

The following equation can be used to determine hourly calorie needs following 60-90 minutes of exercise: 2 calories x lean body weight in pounds

High-glycemic carbohydrates (e.g., energy gels, sports drinks) should make up the majority of calories ingested during a marathon, but inclusion of smaller amounts of protein during a marathon may help enhance endurance performance by as much as 24 percent.

As a means to reap the potential benefits of protein, athletes engaged in prolonged training or racing (more than three hours) should aim at consuming up to 1/8 gram of protein per pound of lean body weight or approximately one gram of protein for every 4-7 grams of carbohydrate ingested.

Personally, I mix my customized formula into a concentrate or paste and place it into a Fuel Belt or gel flask with water. Beyond 60-90 minutes of racing, I'll take shots from my flask along with course-provided water every 15 minutes, which allows my fueling to occur at a steadier rate. It also helps prevent unwanted stomach issues that can arise when too many calories are ingested in a bolus dose.

This is my customized InfinIT Nutrition Formula (per 20-ounce serving): 192 calories, 42 grams carbohydrate, 6 grams protein, 480 mg sodium, 138 mg potassium, 60 mg magnesium. 30 mg calcium

3. Drink Up!

The human body can last a lot longer without food than it can without water. In fact, dehydration (or loss of fluids) can have a profound effect on marathon performance. Runners who blow by the initial marathon water stops tend to be reeled in during the later stages of the race as the onset of "thirst" can trigger an approximate 15 percent decline in their performance capability.

Besides thirst, symptoms of dehydration include muscle cramping, muscle fatigue, nausea, vomiting, diarrhea and chills. In the most severe cases of dehydration, the body's core temperature may increase to 108 F, which if prolonged, will lead to kidney failure and death.

To avoid severe cases of dehydration, runners should aim to replace 0.5-1 liter of fluid each hour during runs, implementing an electrolyte-rich beverage (e.g. sports drink) after 60 minutes of running.

A sports drink should contain the following approximate concentration of electrolytes per 8-12 fluid ounce serving:

Sodium: 150-250 mg

Chloride: 45-75 mg

Potassium: 50-80 mg

Magnesium: 20-30 mg

Calcium: 10-15 mg

Those vulnerable to muscle cramping will also benefit from ingesting a sodium-rich food or beverage as part of their pre-race nutritional plan.