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Star Bulletin Alan Titchenal & Joannie Dobbs Health Options
Alan Titchenal
 & Joannie Dobbs
                   Wednesday, March 27, 2002


Water needs vary with diet and lifestyle

Getting enough water is very basic for good health. However, common recommendations for how much water a person needs each day are frequently presented as too black and white. This week and next week, Health Options will "set the record straight" on commonly asked questions about water needs.

Question 1: Should everyone drink eight glasses of water a day?

There is no perfect answer that applies to everyone. For most people, drinking eight glasses of water a day is more than enough. For some people, it is inadequate.

This common recommendation is loosely based on data showing that a person requiring 2000 calories a day will typically lose about two liters (or about eight 8-ounce cups) of water each day. Most of this water is lost as urine, evaporation from the skin, and from moisture in exhaled air.

If nothing but water is con­sumed, it takes eight 8-ounce glasses of water to replace the loss. But since glass sizes vary and the typical water glass holds between 10- to 12-fluid ounces, drinking eight "glasses" of water (2.5 to 3 liters) can mislead individuals to think that they have an overactive bladder rather than just drinking too much water.

Question 2: Does liquid from other beverages and foods count as part of the water requirement?

Other water sources do count. All beverages and most foods contain significant amounts of water. Fruits and vegetables average around 85 to 95 percent water, meats contain 60 to 65 percent water and even cooked rice is 70 percent water. Most people get three to four cups of water in their food each day.

Consequently, the amount of drinking water a person needs is somewhat dependent on the types of foods they eat.

Question 3: Can coffee, tea, or caffeinated soft drinks be counted as meeting a person's water requirement?

Caffeine is known to increase the amount of water that passes into urine. However, when overall water balance is evaluated, researchers have found that common caffeine-containing beverages can be counted as sources of water.

Question 4: Will drinking water with a meal dilute digestive juices and impair digestion?

No - quite the opposite. Water is an essential part of digestive juices and is needed as part of the chemical process to digest carbohydrate, protein, and fat. Without adequate water in a meal, water will be pulled out of body fluids into the intestinal tract for the digestive process to proceed. Not consuming enough fluid with a meal could temporarily impair digestion.

Question 5: Do you need to increase water with hot weather and exercise.

Anything that increases visible sweat loss or invisible sweat loss will increase overall water needs. Trade winds increase invisible sweat loss and therefore water needs increase if you are outside during those times.

If a person doesn't drink enough water to balance the increased water needs, the kidneys produce a more concentrated urine which increases the risk of forming kidney stones.

New joggers sometimes develop kidney stones because they don't realize how much more liquid they need to consume. It is very common to lose one to two liters of water in sweat during one hour of moderate exercise. During more intense exercise, sweat loss is even greater.

Question 6: How do you know if you are getting enough water?

Pay attention to the sense of thirst and drink enough so that urine looks more like lemonade than apple juice. Supplements or fortified foods high in riboflavin (vitamin B-2) complicate this rule by temporarily turning urine bright yellow.

Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S.
are nutritionists in the Department of Human Nutrition, Food and Animal Sciences,
College of Tropical Agriculture and Human Resources, UH-Manoa.
Dr. Dobbs also works with the University Health Service

© 2002 Honolulu Star-Bulletin --

Human Nutrition, Food & Animal Sciences · University of Hawai`i at Mānoa
1955 East-West Road · Honolulu, HI 96822
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