Marathon Eating 101 - News and Weather For The Quad Cities -

Marathon Eating 101

By Heather Bauer, R.D., nu-train

Running a marathon, or training for any big sport's event, is a huge commitment, and takes months of preparation. Training, however, does not simply consist of sprints, scrimmages, or other heart-pumping related activities. A major component is nutrition. Without proper fuel for your body, you will be unable to reach your maximum potential.

There are four nutrients on which to focus during training. These include water, carbohydrates, protein, and fat. When you drink enough water and eat a balanced diet, your body can work efficiently and provide energy to fuel performance.


Water makes up 60 percent of your body and is involved in essentially every bodily process. Unlike with other nutrients, your body cannot store excess water - you must replace whatever you lose. There is a fine line, however, between drinking too little and drinking too much.
Research Round-up:
Glycemic Index
Exercise Performance

The glycemic index (GI) is a ranking of carbohydrate-containing foods that is based on the food’s effect on blood sugar as compared with a standard reference food’s effect.

Though the GI was originally devised to aid diabetics, it is now extensively used in sports nutrition to aid athletes in the selection of appropriate carbohydrates to choose for training.

In a 2006 study published in the American Journal of Clinical Nutrition, researchers investigated the effects of meals with different glycemic indexes on the metabolic response during exercise in women. Eight active women participated in two trials. In each trial they received a test breakfast 3 hours before performing a 60 minute run. The first trial consisted of a high-glycemic breakfast, while the second was low-glycemic. Researchers found that the low-glycemic breakfast resulted in a higher rate of fat oxidation during exercise than did a high-glycemic meal.

While endurance athletes may require the higher glycemic meal, those individuals desiring weight loss may benefit from consuming lower-glycemic foods prior to exercise.

If you drink too little, you run the risk of dehydration, which hampers performance and increases the risk of heat illnesses, such as heat exhaustion or heat stroke. Conversely, too much fluid puts you at risk for hyponatremia. Hyponatremia is a condition that occurs when the level of sodium in the blood drops too low. Although rare, hyponatremia can result in seizure, coma, or death. Those at risk are people who drink too much and do not adequately replace the sodium lost in sweat.

The best way to prevent hyponatremia and dehydration is to learn the correct way to hydrate.

  • Drink to Hydrate: Your fluid-replacement goal is to drink the perfect amount of fluid, resulting in neither weight loss or weight gain. A helpful tool may be to estimate your sweat rate. Weigh yourself before and after a workout. Then account for fluid consumed during training and add this to the total weight loss.

    For instance, if you lost 1 pound (16 oz) during 1 hour of training, and drank 16 oz, you should drink 32oz (16 + 16) each hour during similar intensity exercise training.

  • Include More Salt: Salt is lost through sweat, so make certain to replace all of the salt lost during training. Consider including more salty snacks (i.e. pretzels or crackers) into your diet.
  • Invest in Sports Drinks: Drinks, such as Gatorade®, help keep your body hydrated while replacing essential electrolytes, like salt, during exercise. Because of the added flavor, you are more likely to consume more. These drinks are preferred over water during long distance or intense training or competition.


Carbohydrates are the preferred source of fuel for the body. They are found in fruits, vegetables, starches, and other foods. The body converts carbohydrates into glucose for immediate energy or stores it in the liver and muscle tissues as glycogen. Muscle glycogen is used during endurance sports. As glycogen is depleted, an individual may become fatigued and unable to maintain training and racing intensity. With high intensity training, 60-70% of calories should come from carbohydrates. Remember: while we usually encourage high fiber and whole grains, opt for low fiber foods (i.e. white pasta, potatoes, etc.) when training to avoid gastric distress and cramping.

  • Stock up before*: Eat carbohydrates for at least several days before competing so that you start with glycogen loaded muscles.
  • Be consistent during: If training or competing for more than an hour, eat carbohydrates during the activity to replenish energy and delay fatigue. Consider energy gel supplementation. A typical gel has 90-100 calories composed mostly of carbohydrates. These are especially helpful during colder days when the sweat rate is lower, and you are not prone to drink as much. Gels, however, can upset your stomach, so try using them to gage your tolerance prior to the competition.
  • Replenish: After a long run or an intense training session, your muscle glycogen stores will be depleted. Therefore, eat a carbohydrate snack of approximately 100-300 calories immediately after training. Snacks may include pretzels, baked chips, or frozen fruit pops.

*A note on carbohydrate (carbo) loading: Carbo-loading is a method some athletes use to maximize glycogen stores. The original method began 1 week prior to the event. For the first 3 days, athletes ate a very low carbohydrate diet (about 10% of total calories) and exercised intensely to deplete glycogen stores. The following 3 days the athlete ate a very high carbohydrate diet (about 90% of total calories) and reduced exercise intensity to maximize glycogen stores. Over the years this technique has been modified and the depletion phase has basically been eliminated. Now athletes usually just increase carbohydrate intake for the 3 days prior to the event (about 70% of calories) and decrease exercise intensity. Consult a physician before attempting a carbo-loading diet.


Protein is needed for muscle and tissue growth and repair. However, too much protein can cause dehydration and muscle heaviness. When muscle glycogen stores are high, protein contributes less than 5% of the energy needed by the body. When glycogen stores are low, protein must be used for energy and may contribute as much as 10% of the energy needed. This process of using protein for energy is expensive and inefficient, and should be avoided as much as possible.

  • Increased Needs: Endurance athletes need up to 50% more protein than sedentary adults.
  • Avoid Excess: Consume no more than 1 gram of protein per pound of body weight. A high protein diet, especially after heavy training will cause incomplete replenishment of muscle glycogen and impair performance.


Fats are required in small amounts by the body for certain critical functions and as an alternative energy source to glucose. Eating too much fat, however, is associated with heart disease, some cancers, and other major problems. A high fat intake probably means you aren't getting enough carbohydrates. Moreover, a high fat diet is difficult to digest and may cause sluggishness.

  • Aim for Moderation: All individuals, including athletes, should consume less than 30% of total calories from fat and less than 10% of calories from saturated fat.

While these basic guidelines will help, we do recommend seeking personalized advice when it comes to intense training. Every body is different, and it is important to make sure you are adequately nourished and hydrated during training and during the event.

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