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How much water do you need?
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Most people have heard the recommendation to drink eight 8-oz glasses of water per day. Why do we need that much water? Does that mean that a 275 lb pro athlete during training camp needs the same amount of water as a 115 lb female office worker whose greatest energy expenditure is walking from her car to the elevator? And does the water we get from fruits, soup, or soda count?
Water is used in every cellular process in the body. It makes up over 80% of the mass of your muscle tissue1 (you didn’t think the “70% of your body is water” was all from blood, did you?). Getting enough water helps clear your skin, keep your digestive system moving smoothly, and helps your brain function properly. It also flushes waste out, both on a large-scale and a cellular level.
The kidneys are your body’s primary filtration system, but need plenty of water to do their job. The liver is responsible for fat and carbohydrate metabolism, as well as protein synthesis (muscle building), but also acts as a backup filter. When there's not enough water in the body for the kidneys to do their job effectively, the liver ends up doing detox duty instead of shedding fat and building muscle. Simply stated: a dehydrated body won’t get the full benefits of exercise.
Warning: science ahead
How much water you need is directly related to how many calories you metabolize, or your “Total Daily Energy Expenditure” (TDEE), combined with water lost through sweating. Since your TDEE is closely related to your body size and activity level, a quick calculation can tell you how much water you should be taking in each day:
Weight in kgs (equal to weight in lbs / 2.2)
x leanness multiplier:
very lean: 1.1
lean: 1.05
normal: 1
overweight: .95
obese: .9
x activity multiplier:
extremely active: 1.1 (this would be a manual laborer who plays hockey every evening)
very active: 1.05
active: 1
light activity: .95
sedentary: .9
x gender multiplier:
women: 1
men: 1.1
= water intake in ounces.
So a 140 lb, normal-build woman who works in inventory control would figure her water intake as 140/2.2 x 1 x 1 x 1 = 63.6 oz of water per day…and there’s the eight 8-oz glasses of water.
Our 275 lb football player during training camp (in the “lean” range) would need 275/2.2 x 1.05 x 1.1 x 1.1 = 158 oz, or almost twenty glasses of water – plus enough to replace whatever he sweats out.
So does that all have to be from drinking plain water? Probably not all of it. Many physiologists say most of your water will come from the food you eat. This approach says any food containing water, and any drink, including caffeinated, sugar-laden, or even mildly alcoholic beverages such as beer count toward your water intake.
The answer is by no means unanimous, however. Most trainers in the sports and fitness world have found their athletes perform better and make more progress toward their physique goals when they drink plenty of good, pure water, maybe flavored with herbal tea or a little lemon or lime juice. People whose main beverages are sodas or coffee often find their energy level increases when they simply up their water intake as well.
The color of your urine is a commonly used indicator of hydration levels (well-hydrated people produce urine that is clear to light-yellow). That can be thrown off, however, by taking vitamins (which will darken the urine), or by caffeine, alcohol, or other diuretics which will cause more water to flush from the body, leaving your urine clear but your body dehydrated.
A better test is to simply feel your lips. When you are well-hydrated, your lips will be soft. If your lips are dry or cracked, you need to drink more water, no matter how much soda you’ve been drinking.
Very plainly, water is critical for body functioning. While it is possible to get too much water (hyponatremia, an electrolyte imbalance caused by over-hydration, is more common, and more deadly, in marathoners than dehydration), it is unlikely to occur in someone who is sipping at their water throughout the day. While physiologists and sports professionals may argue about how much water you need, your body provides some great indicators to let you know how much you should be drinking.
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1Body fat and muscle mass as functions of body water; CSJ, Dec 2007; R.A. Sutton, C Miller
For more info:
The Mayo Clinic page on water intake
Visit Jonathan on the web at www.defylimitations.com
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