Impact of Lack of Food & Water on the Human Body

Food and water are essential to the body. Therefore, dehydration and lack of food greatly impact your body's ability to function properly. Even a temporary lack of food and water can affect your health, and ongoing deprivation is life threatening. The body functions best when you drink about eight glasses of water daily and consume a well-rounded diet.

Importance of Water

Water, second only to oxygen, is essential to human health and without it, you would die within a few days. Water accounts for up to 75 percent of your body weight depending on your muscle ratio. Every tissue and organ in your body requires water to function properly, especially your brain. Water carries out a number of duties, including transporting oxygen and nutrients, lubricating your joints, eliminating toxins and regulating your body temperature.

Dehydration

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The body loses water through urine, sweat and physiological functions such as digestion. Even a modest restriction in water intake can decrease your total water volume and impact your health. A mild fluid decline of 2 percent can impact your ability to concentrate, according to the June 2003 issue of the "European Journal of Clinical Nutrition." Severe dehydration makes it hard for your organs to function and impairs your brain, kidneys and cardiovascular system. Symptoms of dehydration include low urine output, lethargy, no tears, dry mouth and sunken eyes.

Lack of Food

Your body adapts to a lack of food by reducing your metabolic rate to conserve energy. Because glucose is the primary fuel source, fatigue sets in once glucose reserves are depleted. Going several hours without food can cause a noticeable drop in blood sugar. Without enough nutrients from food, your brain function suffers. Children are most vulnerable because they need sufficient food for growth and development. Lack of food affects the academic performance of school-aged children, according to a study published in the December 2005 issue of the "Journal of Nutrition." The study found that food-insufficient children scored lower in reading and math.

Severe Starvation

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Because humans have evolved to survive brief famines, our bodies can survive about 30 days without food. Going a long time without food is detrimental to your health. Your body breaks down fat and muscle tissue to fuel the most important physiological functions. The body becomes unable to produce the proper hormones and enzymes, causing many functions to fail. Your heart muscle shrinks and becomes weak, and you risk going into cardiac arrest. The last organ to shrink and fail is your brain.

Water is the largest single component of the human body, including your brain, and it is essential for life. Generally speaking, people can only survive about a week without water. However, a lot depends on the weather conditions, your level of body fat and your general health status. Being in hot climates, being obese or sick can reduce the amount of time you can survive without water.

Length of Time

Humans cannot survive without water. Because your body can't store it, you must replace the fluid you lose on a daily basis. You need water and other fluids to support functions such as excretion of waste materials and evaporation from your lungs and skin. The U.S. Geological Survey estimates that the average human can survive only a week without water. But exact recommendations about how much water you need are based on a number of other conditions.

Climate

Temperature, humidity level and altitude are some factors that can play into how long you can survive without water. For example, hot and humid conditions can make you sweat more, creating fluid loss that requires you to take in additional fluids to keep your body functioning optimally. In addition, being higher than 8,200 feet often results in more frequent urination and faster breathing, which uses up more of your body water.

Age, Body Fat and Gender

How long you can survive without water also depends on how much total body water content you have. Total body water varies by age, gender and body fat. Men's bodies are composed of about 60 percent water, and women's bodies are composed of about 55 percent. Babies' bodies are composed of about 78 percent water. The higher your body fat, the less the percentage of fluid you have. The less body water you have, the less time you can survive without water.

General Health Status

Illness, such as fever, diarrhea and vomiting, can cause you to lose additional fluids. In addition, taking certain medications -- especially diuretics -- can also exacerbate fluid loss. Being sick can limit the amount of time your body can function properly without replacing lost fluids. On the other hand, engaging in a great deal of physical activity or exercise, even walking long distances because of famine, can increase the amount of water you need to survive.

Water Intake Recommendations

The Institute of Medicine states that most adult men need about 3.7 liters of water daily and women 2.7 liters. Water is best, but you can meet some of your water intake needs through other kinds of fluids as well as foods that have a high moisture content. Toddlers up to age 3 years, need about 1.3 liters daily, and between ages 4 and 8, roughly 1.7 liters is considered adequate intake. Boys between the ages of 9 and 18 need between 2.4 and 3.3 liters daily; girls in that age range need between 2.1 and 2.3 liters. Pregnant and nursing moms need 3 and 3.8 liters, respectively.