Water is more important to health than most people realize¾and many of us don't drink enough of it. This powerful marriage of hydrogen and oxygen is the most abundant and essential nutrient in the body. It accounts for 60 percent of your weight if you're a young adult and 50 percent if you're elderly. (Why the age difference? Not because old people are "dried up," as popularly supposed, but because their bodies contain less muscle, which is 65- to 75-percent water, and more fat, which is only 50-percent water.)
Of the myriad functions that water serves, among the most important are 1) acting as the medium in which most of our body's chemistry occurs, 2) helping to excrete waste, and 3) cooling us through evaporation from the skin and inner surfaces of the lungs.
It's Easy to Run Short...
Consuming too little water can upset your balance of electrolytes (substances that conduct electrical signals in nerves, muscles, and cells) and impair your physical strength. (Studies show that a loss of water amounting to only 2 percent of body weight will mar athletic performance.) Water shortage can also interfere with the digestion, absorption, and utilization of other nutrients, and has been linked to bladder cancer.
Unlike energy, which can be stored as fat, a certain fraction of the body's water must be replaced every day. The 24-hour turnover depends on temperature, humidity, altitude, degree of exercise, and whether you're taking diuretic drugs. It averages about 4 percent, which means that if you weigh 150 pounds, you need to replace about 12 eight-ounce glasses of water each day.
...But There's Water Everywhere
You don't have to drink that much, however. Your body manufactures one glass of water each day from the carbohydrates you eat, by breaking them down and putting some of their hydrogen and oxygen back together as H2O.
In addition, most foods contain a lot of water. Coffee and tea are more than 99-percent water;* milk and soft drinks, about 90-percent. Most fruits and vegetables are 90-percent water—that's why they shrivel so much when dried, and why iceberg lettuce actually contains a higher proportion of water than orange juice does. Even meats and cheese are half water.
For this reason, even if you've had nothing to drink so far today, you may find the chart in Today's Nutrient Intake showing you've consumed quite a lot.
Thirst Is a Liar
You can't always trust your sense of thirst to keep your water intake above the minimum required for good health. An hour of hard work or athletic competition that involves heavy sweating, for example, can dehydrate the body far beyond what a person would ordinarily feel like drinking. Similarly, people who are sick or elderly often have a dulled sense of thirst.** In instances like these, it's better to trust objective guidelines than your own feeling of satiety. For more on this point, see "How Much to Drink," below.
Incidentally, the common belief that caffeinated drinks don't count toward water intake is false. The amount of water they supply vastly outweighs their diuretic effects.
A 2002 study by the U.S. Department of Agriculture concluded that "more than one in three Americans over the age of 60 may not be consuming enough water."
Your Daily Allowance
In February 2004 the U.S. Food and Nutrition Board (FNB) announced an official Adequate Intake (AI) of water. Expressed in fluid ounces, the AI for males is 111.6 from age 14 to 18 and 125.1 thereafter. For females it is 77.8 from age 14 to 18 and 91.3 thereafter. For women who are pregnant or lactating it's 101.4 and 128.5, respectively. Diet Power sets your Personal Daily Allowance (PDA) at the AI. If your doctor recommends getting more or less than that, you can change your settings with the Personal Daily Allowance Editor.
(NOTE: Your PDA of water and the amount you specify in your WaterMinder™ are independent. Changing one does not change the other.)
The FNB has not established a Tolerable Upper Intake Level (UL) for water.
How Much to Drink
Your PDA of water does not take into account fluids lost through sweating (except the low-level, invisible perspiration that's normal for everyone), because sweating varies widely with the individual, the activity, and temperature and humidity. So, besides consuming your PDA of water, you need to drink enough to replace any you've lost through visible sweating.
It is surprisingly easy to get too little water while perspiring. Thirst isn't always a reliable indicator¾you may have to force yourself to drink enough.
To improve performance and help to prevent dehydration, the American College of Sports Medicine recommends drinking a pint (16 fl oz) of water a couple of hours before your workout. If the workout lasts longer than an hour, it's wise to drink fluids during the activity, too.
Afterwards, you should drink enough water to bring your weight back to normal¾two cups for each pound you've lost. (Remember the old mnemonic: "A pint's a pound the world around.")
If you're using plain water, however, don't drink it too fast. Ordinary water can dilute your body's concentration of electrolytes, causing confusion, nausea, fatigue, muscle cramps, and weakness¾and sometimes vomiting, muscle twitching, delirium, seizures, and coma. An average adult should drink no more than 1-1/2 quarts (44 fl oz, or about five glasses) of plain water per hour or 12 quarts in 24 hours. If you're rehydrating at anywhere near this rate, it's safer to use sport drinks such as Gatorade and POWERade, which contain electrolytes.
Diet Power now includes a utility that can alert you when your water consumption is low. See WaterMinder™.
Color Coding of This Nutrient
The water bar in your personal Nutrient History is:
blue for "good" if you've logged 100 percent
or more of your PDA
red for "bad" if you've logged less than 100
percent of your PDA
missing if you've logged no water
In the nutrient profile of a food or recipe, the water bar is:
green for "good" if getting your entire PDA
of calories from this item would give you more than 150 percent of your
PDA of water
magenta for "bad" if getting all your calories
from the item would give you less than 50 percent of your PDA of water
blue for "neutral" otherwise
missing if the amount of water is either zero or (when the word Water is grayed out) unknown
How Complete Are Diet Power's Water Readings?
For the 8500 generic items in the Food Dictionary: very complete. Only 1 percent list their water content as "unknown."
For the 2500 chain-restaurant items: totally incomplete. All list water as "unknown." (Whenever you add a beverage to the Food Dictionary, it's wise to estimate its water content instead of leaving the Water field blank. Otherwise, your WaterMinder and your Nutrient History will get a mistaken notion of your water intake every time you log the beverage. About 11.5 fluid ounces of water in a 12-fluid-ounce serving is a fair estimate, since most beverages are 93% to 99% water. To estimate more accurately, check the nutrient profile of a similar beverage that's already in the dictionary.)
For all 11,000 items combined: not terribly complete. About 21 percent list water as "unknown."
These figures mean that if you frequently log chain-restaurant foods (or user-added foods with missing water readings), your Nutrient History may underreport your intake of water by a few points.
To see whether a particular food has a water reading, open the Food Dictionary and check the food's nutrient profile. If you find a question mark beside "Water," it means the amount is unknown. (To see all foods with unknown water readings, click the dictionary's PowerFoods tab and sort the foods by water power; then scroll toward the bottom of the list until you see foods with question marks in the "Power Rating" column.)
Water on Food Labels
Nutrition labels are not required to report water content, and there is no official Daily Value for water. (The Diet Power Daily Value is 108 fluid ounces, midway between the AI for most males and most females). Generally speaking, almost any drink that has the consistency of water is more than 90 percent water. The main exception is alcoholic beverages, where alcohol may replace up to 50 percent of the water. See Alcohol.
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Last Modified: 1/1/07