Food for thought from…
Peggy Balboa, Registered Dietitian, Mariano’s
The importance of staying hydrated.
Improper hydration plagues the marathon competitor. Dehydration increases the potential for cardiovascular stress, risk of heat illness, and reduced exercise capacity. Beginning the race hydrated and staying hydrated is essential for running a successful marathon.
But how much fluid is needed to stay hydrated? A fully hydrated 70kg (155 lbs.) adult male will average a total body water weight of approximately 60%. During a marathon, this runner could lose water at an estimated 1-2 L/hour, or more depending upon conditions. Consuming appropriate amounts of fluid on the days leading up to the event will ensure fluid losses are being replaced.
By calculating sweat rate, you will know how much fluid is needed during each hour of the marathon. Practice consuming this amount of fluid prior to event day to understand the maximum volume your stomach can tolerate during exercise without discomfort. Fluid expands the stomach and can cause delayed digestion. Try 300-400 mL of water (10 to 12 oz.) prior to a practice run to test stomach tolerance.
Begin the marathon fully hydrated.
Prevent dangerous fluid losses during competition by beginning the marathon fully hydrated. Good sources of fluid include water, sports drinks, juices, soups, smoothies, fruits, and vegetables.
The American College of Sports Medicine (ACSM) recommends consuming about 5 mL/kg to 7mL/kg (or 300-600 mL) of fluids at least four hours before exercise, along with a pre-event meal. Water is usually sufficient to hydrate before a race, but water along with sodium from food encourages fluid consumption and helps the body to retain water. Within 15-20 minutes of the marathon, take in another 300-450 mL.
During the marathon, hydrate with water and carbohydrate.
Carbohydrates play a role in rehydration. Too much carbohydrate consumed with fluid will delay gastric emptying and may cause abdominal pain. The amount of carbohydrate consumed with fluids during the competition will determine the effectiveness of rehydration and contribute to energy. Consuming 30-60g of carbohydrates per hour of exercise will lead to effective use of energy and fluids during exercise and decrease the likelihood of any abdominal pain.
Optimizing and maintaining proper hydration without overdrinking is a balancing act. To reduce the risk of developing hyponatremia (low blood sodium levels caused by excessive water consumption), sports drinks work well during prolonged exercise. Generally, 4-6 oz of fluid every 15-20 minutes after 30-60 minutes of exercise is recommended. Getting carbohydrate, fluid, and electrolyte can be easily achieved by consuming sports drinks containing 6-8% carbohydrate and 0.5 g/L-0.7 g/L of sodium.
Congratulations, you have finished the marathon!
Now that you have finished the marathon, safely rehydrate to replace all of the fluids and electrolytes lost during competition. Over time, athletes are encouraged to consume 125%-150% of fluid lost during exercise. Determine the fluids needed to rehydrate by using the sweat rate calculated prior to the race.
In addition to fluids for rehydration, don’t forget to replace the sodium lost during competition. Consuming foods with sodium post-race will help stimulate thirst and aid in retaining fluids taken into the body. Examples of salty snacks include pretzels, chips, jerky, pickles, and broth.
Written in conjunction with Peggy Balboa by:
University of Illinois at Chicago Dietetic Intern
American Dietetic Association. Nutrition Care Manual®. Fluid. http://www.nutritioncaremanual.org/content.cfm?ncm_content_id=92181. Accessed March 23, 2010.
Burke L & Deakin V. Clinical sports nutrition. New York:McGraw-Hill, 2010
Mahan LK, Escott-Stump S. Krause’s Food and Nutrition Therapy. Canada:Elsevier, 2008.