Q&A: Marathon Hydration and Nutrition

By Dr. Craig Norswill | July 28, 2009, 12 a.m. (ET)
How do you prepare for a marathon or long-distance race? Gatorade Sports Science Institute Scientist Dr. Craig Horswill answers questions about marathon hydration and nutrition.

Q.    My running partner’s hydration plan works well for her.  Can I just copy her plan?
A.     Having an individualized hydration plan is a great idea for every endurance athlete.   But since everyone sweats at a different rate, it’s important to follow your own plan.  You can easily do this by estimating your personal fluid loss.  To start, weigh yourself before and after training and competition with the goal to weigh the same before and after exercise. The weight loss represents fluids lost from the blood and muscle. If you lost weight, drink more next time.  If you gained weight, cut back on your fluids.  Keep in mind sweat rates can vary depending on environmental conditions, so be sure to calculate it in various situations. Remember to replace what you lose – which includes critical electrolytes, like sodium, but don’t replace more than what you lose. Visit GSSIweb.org for more information.

Q.    I think I might be dehydrated, but I’m not sure.  What is the best way to tell?

A.    Other than weighing in and out after training, there is no “best” way to tell if you are dehydrated. One easy way to predict if you’re properly hydrated is to check the color of your urine. If your urine is pale like the color of lemonade, that’s a sign of good hydration.  Crystal-clear urine often indicates over-hydration and the need to cut back on fluids.  Dark urine (like the color of apple juice) may signal dehydration and the need to drink more.  

Q.    When should I drink water and when should I drink a sports drink?  Can I drink both or is it one or the other?

A.    When training for an endurance event like a marathon, your beverage choice matters.  Water is an option for short distances.  Look for a sports drink/beverage with electrolytes and carbohydrate to help replace the electrolytes you lose in sweat, promote rapid absorption, and supply energy especially during long distance events..

Also, find out what will be offered on course and consider training with it.  By the time you get to your competition, you’ll know what works best for you and what to avoid.

Q.    I worry about dehydration so I carry fluids with me and drink the entire time I run.  Is that okay?
A.    Staying hydrated during your run is important, however, whatever your beverage preference is, it’s essential not to over-drink.  Over-hydrating can lead to a dangerous condition called hyponatremia.  The risk of hyponatremia can be reduced by making certain your fluid intake does not exceed your sweat loss and by ingesting sodium-containing beverages or foods to help replace the sodium lost in sweat, particularly during long runs. 

Q.    In addition to fluids, what else do I need to make sure I’m not running on empty?
A.    Good question.  You definitely don’t want to run out of fuel.  It’s important to start with a full tank.  Fuel your body 2 to 3 hours before training and competitions.  Consume high-energy foods like breads, cereals, pasta, rice, and fruits.  During activity, endurance athletes should consume between 30 and 60 grams of carbohydrate per hour to help fuel muscles and sustain your optimal performance. This can come in the form of a sports drink, gels, bars or concentrates, all of which have various amounts of carbohydrate. Gatorade Endurance Formula (EF) is served on the course of the Bank of America Chicago Marathon. Drinking one half liter per hour of EF will provide 30 g of carbohydrate.
Remember that everyone is different, so what works for one person might not work for the next.  I recommend testing out your own hydration and nutrition plan during training so you can have optimal results on race day.

Dr. Craig Horswill is a Senior Research Fellow at the Gatorade Sports Science Institute (GSSI) where the research team studies the effects of nutrition and hydration on physical performance and well being. The Institute has worked with athletes at all levels – from collegiate to professional, from children to Olympians – to help them with their sports nutrition and hydration needs.  Dr. Horswill has published numerous peer-reviewed studies in journals such as the Medicine and Science in Sports and Exercise, International Journal of Sport Nutrition and Exercise Metabolism and International Journal of Sports Medicine. Dr. Horswill is a member of the American College of Sports Medicine.