Here are five general hydration and nutrition tips for long-distance runners, keeping in mind that all runners have individual needs, depending on their conditioning and overall health:
Pre-race hydration. On the morning of the marathon, make sure to drink about 8 to 16 ounces of fluid to properly prepare. But you probably should stop drinking about one hour before the start to avoid early stops along the course.
A cup every other mile. A general guideline for marathoners is to drink 3 to 6 ounces of fluid every 15 to 20 minutes. This averages out to grabbing a cup of water or a sport drink every other mile. This depends on how crowded those water stops are during the race. Additionally, you may need to drink more if the weather is hotter than usual.
Know your sweat rate. The most accurate way for figuring out your fluid need is to take a sweat-rate test during your training. Weigh yourself without clothes before and after a one-hour run. Convert the amount of weight lost to ounces to figure out your sweat rate per hour. A loss of one pound means you sweated about 16 ounces of fluid (assuming you didn’t drink any fluids during the run. Otherwise, you would take into account any fluids taken). You should try to replenish fluids at a rate of about 16 ounces per hour.
Chase your energy gels with water. If you take those “energy” gels with a sport drink, then you risk ingesting too much sugar, which can cause stomach cramps or even diarrhea. If you take gels, chase them down with water. Remember that sports drinks generally provide the same electrolytes that are in gels.
Make a plan for race-day hydration and nutrition. Most runners carry water, sports drinks or gels in case the volunteers along the course run out of cups or those stops get too crowded. Develop a plan so you know what and when you’ll eat and drink. Make sure that includes drinking and consuming calories within 30 minutes to an hour after the start. You shouldn’t wait too long before starting to hydrate properly.