Taking in enough fluids each day is important for everyone, regardless of your level of activity. While individual needs vary, the National Academy of Sciences recommends 2.7 liters a day for women and 3.7 liters a day for men. “This number includes both beverages and other fluids as well as fluid your body processes from foods like veggies and fruit,” says Heidi Skolnik, MS, CDN, FACSM, sports nutritionist at the Women’s Sports Medicine Center at HSS, adding that 20 percent of our fluid needs come from food. This leaves approximately 9 cups of fluids for women and 13 cups for men that still need to be consumed each day.
Hydration is particularly important for runners. “Running and sweating increases the amount of fluid we need,” says Skolnik. This can potentially lead to dehydration, which can cause symptoms including headache, rapid heartbeat and fatigue—and it can also slow you down during your run. “Dehydration is influenced by multiple factors, including temperature and humidity, the length and intensity of your run, your body weight and your own personal sweat rate,” adds Skolnik. She offers these tips to help keep dehydration from derailing your progress.
Thirst is an obvious sign that you need more fluids. But “as we get older, our thirst sensation may lesson,” says Skolnik. “As we exercise and we dehydrate, our thirst mechanism may not keep up.”
One way to check whether you need more fluids is to consider your pee. If you pee less often, a lesser amount than usual, or it’s darker than straw yellow, that indicates you’re dehydrated, she says.
Another way to monitor your fluid intake when running that can also give you a better sense of your personal sweat rate is to weigh yourself before and after you run. Make sure you have minimal clothing on (“Nude is even more accurate,” Skolnik says) when weighing yourself and noting your “before” weight. After your run, wipe the sweat off your body, then take your “after” measurement. “Make sure to add back to your ‘after’ weight any fluid you had while running,” she says.
For example, say you ran for 90 minutes, and you weighed 164 pounds before your run and 163 pounds after. During your run you drank 8 ounces of water. Adding the 16 ounces from the pound you lost, as well as the 8 ounces of water you drank, adds up to 24 ounces of total sweat loss. Dividing that number by the time you spent running will leave you with your sweat rate. “If you’ve lost more than 2 to 3 percent of your body weight in sweat during your run, it’s time to be more strategic about your fluid intake while running,” Skolnik says.
Getting enough fluids during your run is just one part of the equation. “You’ll have a much easier time staying hydrated if you make it a part of your overall fueling plan,” Skolnik says. Just keep in mind that more is not better. “Overconsuming water will not make you more hydrated, and can actually be harmful,” she explains, as your kidneys will note you have reached your limit and signal you to pee more.
All beverages count toward your fluid needs, says Skolnik, including juice, milk, plain or flavored seltzers, herbal tea and even caffeinated teas and coffee. “If plain water bores you, try adding some berries, sage, or cucumber slices to a pitcher of water and letting them soak overnight, and you’ll have flavor infused water to sip on throughout the day,” she suggests.
During your runs, cool or cold water is always a good option, especially on runs less than 60 minutes. Sports drinks provide carbohydrates to help delay fatigue and electrolytes to help with fluid balance. This is particularly important when your run is longer (more than 60 to 90 minutes), unusually intense, or in extreme conditions, such as high temperatures or altitude, Skolnik says. Sodium, an electrolyte that is essential to fluid balance, is extremely important to take in along with fluids when sweating heavily.
Another fun tidbit is that the stomach is also trainable and adapts with practice. “You actually can train your gut to maximize absorption and help you run strong,” Skolnik says. As your miles increase, make it a habit to up your fluid and carbohydrate intake as well. When running for more than one hour, coordinate hydration (including sodium) with fueling, she advises. “‘Chunking’ your runs into 15-to-20-minute segments and starting hydration and fueling early will help you stay ahead of your needs.”