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Nutrition For Ultra-Endurance Athletes!

An in-depth look at all of the nutritional considerations for competing in ultra-marathon events. Topics include hydration, pre/post event eating, and carbs.

An in-depth look at all of the nutritional considerations for competing in ultra-marathon events. Topics include hydration, pre/post event eating, and carbs.

USA Today recently came out with their top 10 most difficult things to do in sports-- # 7 was running a marathon. This seems like a pretty daunting task, but imagine swimming 2.4 miles and biking 112 miles before ever starting that run. This is exactly what an ironman triathlete has to do just to finish their event. Keep in mind, the fastest athlete will finish a race in 8 or 9 hours; a true test of strength, endurance and willpower.

    USA Today's 10 Hardest Things To Do In Sports:

    1. Hitting A Baseball
    2. Race Car Driving
    3. Pole Vaulting
    4. Hitting A Long Straight Tee Shot
    5. Returning A Serve
    6. Landing A Quad
    7. Running A Marathon
    8. Tour De France
    9. Saving A Penalty Kick
    10. The Downhill
Read the full story here.

Nutrition is one of the key factors in determining where you will finish, or if you will even finish at all. Let's take a look at various aspects of nutrition in relation to these ultra-endurance events.


An athlete's hydration status is the single most important factor affecting overall performance. Numerous studies have shown that an individual's endurance gradually decreases the more they become dehydrated. Dehydration is usually a result of sweat loss, expiration and inadequate fluid intake. If this trend progresses, serious medical complications can result.

For example, a 3% decrease in total body weight has been shown to adversely affect performance, while a 5% decrease in weight can cause heat cramps and nausea (1). If proper fluid replacement isn't started, this could eventually lead to heat exhaustion, heat stroke and possibly death. Keep in mind, the best ways to evaluate hydration status are through weight lost and the color and quantity of urine.

Luckily, most athletes who compete in ironman triathlons are aware of the dangers of dehydration. The same cannot be said for the dangers of overhydration. This is much less common, but is gaining more attention because of the popularity of ultra-endurance events. Overhydration usually occurs when an athlete is performing in hot weather, is sweating profusely, and is replacing lost fluids with plain water.

When an athlete loses sweat, they are also losing large amounts of sodium, which is the main electrolyte involved in fluid balance. This sodium loss, coupled with minimal replacement from water, can lead to hyponatremia or low serum sodium levels in the body. This is a serious condition which requires immediate medical attention.

The best way to prevent complications from both dehydration and hyponatremia is to drink adequate fluids early and often, preferably those containing electrolytes such as sodium and potassium. Research has shown that athletes competing longer than 6-8 hours may need up to 1 gram of sodium per hour to replace losses (2). Some of this can be replaced by using sports drinks (i.e. Gatorade and Powerade) before and during the event. Sodium has a dual role in these beverages whereby it improves flavor and helps increase blood plasma volume (3). It's important to remember that the sodium in these drinks may not be enough for repletion needs; some athletes also eat sodium-containing foods and/or use salt tablets toward the end of an event.

Below you will find hydration guidelines for before, during and after ironman events (4).

    Before Event:
    16 oz. 2 hours prior, then 4-8 oz. 5-15 minutes prior to start

    During Event:
    5-10 oz. every 15-20 minutes

    After Event:
    16-20 oz. per lb. of body weight lost


Triathletes expend an incredible amount of energy during their training and, in turn, have to consume plenty of calories on a daily basis to stay in peak form. Energy demands can be variable and depend upon the duration, intensity and type of exercise training (5). One ultra-endurance athlete competed in a run around Australia and ran an average of 70-90 kilometers per day (80 km equals approx. 45 miles) and consumed an average of 6,321 calories per day.

It's hard to believe he needed this much energy, given the fact that his basal metabolic rate was estimated to be 1,597 calories per day (6). Trying to match calories in with calories out is a difficult challenge. These athletes often need to eat several meals a day and may consume a variety of nutrient-dense foods and liquid shakes. Another factor affecting performance is the actual nutrient breakdown of the diet in terms of carbohydrates, fats and proteins.

Carbohydrates are the foundation of any nutrition regimen when training for an ironman triathlon. Unfortunately, your body only has a limited amount of carbohydrate reserve for endurance events. As an example, a 150-pound man has approximately 1400 calories of muscle glycogen (stored sugar), 320 calories of liver glycogen and 80 calories of blood glucose (1).

For comparison, this same individual would have almost an unlimited supply of fat calories to use for energy. As the intensity of exercise increases during training, more carbohydrate will be used for energy because it can be processed faster. However, when the muscle and liver stores are depleted, the body will have to pull from the blood sugar. When this happens, you are on steady path toward fatigue. This is what some of us like to call "hitting the wall."

One way to avoid this decrease in performance is to consume adequate carbohydrates before and during training and events. Another way is to maximize muscle and liver glycogen by carbo-loading. This involves tapering training one to two weeks out from an event and then maintaining a high carbohydrate diet (usually 70% of calories). Eating a meal three to four hours before an event is also part of this loading regimen and can result in improvements in endurance (5). This is a common practice among ironman triathletes.

It's important to note that chronic fatigue can still occur if glycogen is not repleted after exercise. Consuming adequate carbohydrates after exercise sessions will help prepare you for the next training day.

Below you will find daily carbohydrate recommendations, in addition to that needed before, during and after ironman events (1).

To calculate your needs automatically, enter your bodyweight in pounds and click CALCULATE.

Enter Your Bodyweight In Pounds: Pounds

Press Calculate To View Results Below

Results And Guidelines:

    Daily Needs:
    3.0 to 5.0 gms per lb. of body weight per day
    Your carbs per day: Between and grams.

    Before Event:
    0.5 to 2.0 gms per lb. of body weight (1-4 hours prior)
    Your carbs before event: Between and grams.

    During Event:
    30-75 grams per hour

    After Event:
    0.5 gms per lb. of body weight every 2 hours (recovery)
    Your carbs per hour after event: grams.

Until now, the focus has been on carbohydrates, however fat is one of the main reasons that triathletes are able to compete for several hours at a time. As an athlete's effort becomes more steady state, fat becomes a major contributor to energy utilization, in turn sparing carbohydrate for when the intensity picks back up. The guideline for fat intake is usually estimated to be at least 0.5 gms per pound of body weight per day, similar to a typical heart-healthy diet (4). This is because the body has abundant stores of fat and can utilize this for energy. The dietary fat is important because we need the essential fatty acids, which have several functions in the body.

Protein is the last of the macronutrients that a triathlete needs for optimal performance. This nutrient is not typically known as a major energy contributor during exercise, but in the fed state, it may provide up to 5% of the fuel used. As exercise duration increases, protein utilization can increase as well, maintaining blood glucose through a conversion process in the liver (7). It is important for ironman triathletes to consume protein with their meals, especially during recovery, as this will help to repair injured tissues. The typical recommendation for protein intake is 0.55 to 0.65 gms per pound of body weight per day; more than the RDI, but less than what is recommended for strength and power athletes (4).

Daily Protein Auto-Calculator

Enter Your Bodyweight In Pounds: Pounds

Press Calculate To View Results Below

Results - Protein Per Day:

Between and grams.

About The Author

Brian Zehetner MS,RD,CSCS is a sports nutritionist and fitness professional living in Minneapolis, Minnesota. If you have any questions or comments regarding sports nutrition and performance, feel free to call him at 612-822-8745 or email him at


  1. Clark, N. Nancy Clark's Sports Nutrition Guidebook. 2nd ed. Champaign, IL: Human Kinetics; 1997.
  2. Clark, N., Tobin J. Jr., Ellis, C. Feeding the Ultra-Endurance Athlete: Practical Tips and a Case Study. Journal of the American Dietetic Association. 92: 1258-1262, 1992.
  3. Rehrer, NJ. The Maintenance of Fluid Balance During Exercise. International Journal of Sports Medicine. 15: 122-125, 1994.
  4. Rosenbloom, CA. Sports Nutrition: A Guide for the Professional Working with Active People. 3rd ed. Chicago, IL: The American Dietetic Association; 2000.
  5. Applegate, EA. Nutritional Considerations for Ultra-Endurance Performance. International Journal of Sport Nutrition. 1: 118-126, 1991.
  6. Hill, R. J., W. Davies, Peter S. Energy Expenditure During 2 Weeks of an Ultra-Endurance Run Around Australia. Medicine & Science in Sports & Exercise. 33: 148-151, 2001.
  7. ACSM, ADA, Dietitians of Canada. Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise. 32: 2130-2145, 2000.

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