Water is the primary building block of cells and acts as an insulator, regulating internal body temperature. Water is needed to metabolize proteins and carbohydrates used as food, and is the primary component of saliva -- used to digest carbohydrates and aid in swallowing food. Water lubricates joints, acts as a shock absorber, and insulates the brain, spinal cord, organs, and fetus. Water is used to flush waste and toxins from the body via urine and is the principal solvent in the body. It dissolves minerals, soluble vitamins, and certain nutrients. Also, water carries oxygen and nutrients to cells. Water plays a vital role in the body's regulation, protection, and function.
When I was running solo across America in temperatures that were typically around the 100-degree mark, I would drink at least two gallons of water on a 35-mile day as my body exerted tremendous energy covering the distance while pushing a jogging stroller averaging 65 pounds in weight. Even at the office, I drink water regularly and it is the only form of liquid I drink during the work day. The percent of water in your body depends on your hydration level. People feel thirsty when they have already lost around 2-3% of their body's water. Mental performance and physical coordination start to become impaired before thirst kicks in, typically around 1% dehydration.
So, how much water should you drink each day? There are many different opinions! The health authorities commonly recommend eight 8-ounce glasses, which equals about 2 liters, or half a gallon. This is called the 8×8 rule and is very easy to remember. However, there is also a way to calculate how much water you should drink daily based on your weight. For instance, a 200 pound man and 100 pound woman require different amounts of water every day. To figure out how much water to drink each day based on your weight, I've read that you multiple your weight by 2/3 (or 67%). For example, if you weigh 190 pounds, you multiple that by 2/3. That would mean that you should be drinking about 127 ounces of water every day (or 1 gallon). If you want to adjust that number based on how often you work out -- since you are expelling water when you sweat -- you should add 12 ounces of water to your daily total for every 30 minutes that you work out. As an example, if you work out for 45 minutes daily, you would add 18 ounces of water to your daily intake.
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