Water is essential to human life. Although you might survive weeks without food, you can only live a few days without water. All your bodily systems and organs need water to function. Your body naturally loses water daily, and when it fails to replace this loss, you become dehydrated. Dehydration causes your body's basic processes to slow down, eventually leading to a temporary decrease in your metabolism.
Signs of Dehydration
You lose water through sweat, urine, feces and your breath. Hot temperatures and physical exertion increase the rate at which you lose water. Thirst, headaches and fatigue are common symptoms of mild dehydration. Dizziness, infrequent urination, a sticky mouth and muscle cramps are other symptoms. Severe dehydration can result in confusion, chills, low blood pressure and a rapid heart rate.
A loss of 1- to 2-percent of your body's water content is often enough to make you thirsty, but sometimes people don't feel thirsty until they're almost 3 percent dehydrated. On a cool day, mild dehydration isn't debilitating, but in hot weather, it can compromise physical performance and contribute to heat-induced illness. If you reach 5 percent dehydration, your performance may suffer even more dramatically.
Metabolism Slows During Dehydration
Your metabolism helps make possible the activities your body does daily to burn calories, including basic functions, such as exercise, chores and simple movements. Dehydration can slow down all these functions and cause you to burn fewer calories.
When cells are deprived water, or fluid, they shrink slightly. The body senses the change in cell size and uses it as a signal to slow metabolism. When people experience 3 percent dehydration, their metabolism diminishes by about 2 percent, reported University of Utah researchers in 2003. If you regularly burn 2,000 calories daily, that means you burn about 40 calories fewer per day.
Fluid Needs for Adequate Hydration
Women need approximately 91 ounces of water daily and men, 125 ounces, according to the Institute of Medicine. People who live in hot climates or those who exercise a lot need more. You get about 80 percent of your water from beverages and the remaining 20 percent from the food you eat. Regularly eating water-rich foods, such as fresh fruits and vegetables, help increase your fluid intake.
You don't have to count glasses you drink daily to ensure hydration. Instead, check the color of your urine, which should be a pale, straw-like color. Be aware that certain medications and supplements can alter the color of your urine. A simple test of skin turgor, or rigidity, also helps you judge hydration. Pinch the skin at the back of the hand or lower arm into a tent. Hydrated skin should snap back rapidly.
Staying Well-Hydrated During Exercise
Exercise increases your risk of dehydration, especially if you do so in hot or humid conditions. An active lifestyle means you need to drink more to keep your fluid levels balanced. In addition to drinking water regularly throughout the day, drink about 20 ounces of water in the hours leading up to your workout. Sip another 8 ounces 20 to 30 minutes before beginning. For every 20 minutes while you exercise, take in 7 to 10 ounces of fluid. After your workout, drink another 8 ounces and 16 to 24 ounces for every pound lost during the session.
Dehydration can make you lethargic and tired -- interfering with your daily movement, which makes up 30 percent of your metabolism. To maximize this aspect of your metabolism, stay hydrated so you feel good enough to exercise, walk and do chores.