Adam’s Journal
In case you haven’t noticed, it’s gotten kind of soupy out there. Not surprisingly, the summer’s heat and humidity have been most evident during my morning runs. I feel like I should be apologizing to my wife for the sweat-saturated clothes that decorate our bathroom for the remainder of the day.
How much water do I need to be drinking to replace all that lost fluid? Is the usual recommendation of eight glasses a day sufficient?
Dr. Scofield Prescribes
Like its cousin the 10,000 steps-a-day “rule,” the belief that we must drink eight glasses of water has no scientific basis.
The concept likely stemmed from a 1945 Food and Nutrition Board recommendation stating that each day people should drink 2.5 liters of water, a bit more than eight glasses (which equals a half gallon). However, that recommendation failed to take into account some important factors.
First, we’re all different, and how much water we need ties directly to our individual sizes, metabolisms and sweat rates. Second, the amount of water we need also correlates to our environments and activity levels. If you’re exercising vigorously outdoors in July, you’re going to require more than if you’re spending that time stretching indoors.
The best gauge for proper fluid replacement is to figure out how much fluid you’re losing. To do this, weigh yourself (naked is best) before your usual workout. Then go outside and do your thing.
When you’ve finished, but before you have anything to drink, weigh yourself (naked again). Take the difference in pounds and multiply it by 16 ounces. That’s how many ounces of fluid you need to replace.
So, if you lose 2 pounds, 2 x 16 = 32. That means you need 32 ounces to make up for what you just sweated out.
For this to function as a good general rule, you should do this test under circumstances as similar as possible to your usual routine. That means if you usually work out on hot summer mornings at 6:30, test at 6:30 on a muggy morning and exercise at your typical level of exertion.
It also helps to do tests in a “round” time period – say, 30 minutes. That way, you can do some simple math whenever you exercise more or less. In my example, you’d only need to replace 16 ounces if your workout one day lasted 15 minutes, while you’d want 64 ounces if you exercised another day for a full hour.
When you’re exercising, it’s always smart to start replacing fluid mid-workout; the longer and hotter the workout, the more important this is. And especially when you sweat vigorously, you’re also losing salt and other electrolytes, so don’t forget to replace those, too.
In short, there’s no one-size-fits-all number. But water and fluids are always a good decision. If in doubt, drink up!
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Dr. Hal Scofield is a physician-scientist at the Oklahoma Medical Research Foundation, and he also serves as Associate Chief of Staff for Research at the Oklahoma City VA Medical Center. Adam Cohen is OMRF’s senior vice president and general counsel. Send your health questions to contact@omrf.org.
