Water Is an Essential Nutrient
What foods and beverages provide water?
If we combine these routes of water loss from our body, it totals about 2 to 3 L (2 to 3 quarts or 8 to 12 cups) per day. If the amount of water lost from the body is not at least matched by the amount of water provided to the body, then dehydration can occur. However, this does not necessarily mean that we need to drink eight to twelve cups of pure water every day because there is water in most of the foods we eat, including water-based fluids such as milk, coffee, tea, juices, and drinks such as soda, Kool-Aid, sport drinks, etc. On the average we drink about 1 L of water daily in the form of water or other fluids such as soft drinks. Also, we receive about 1 L of water in the foods we eat Foods such as fruits and vegetables will have a relatively high water content compared to meats, breads, and fats.
Can we produce water in our body?
In addition to the water we ingest, we can also count on normal metabolic reactions in our cells to generate some water as well. On average an adult will generate about ½ liter (~2 cups) in our normal metabolic reactions. When our cells completely break down (combust) the glucose and the fatty acid, two of our most significant energy nutrients, water is created.
Glucose: C6H12O6 + 6 O2  6 CO2 + 6 H2O
Palmitic Acid: C16H32O2 + 23 O2  16 CO2 + 16 H2O
What is thirst?
When our body needs water, a region of our brain called the hypothalamus initiates thirst. Thirst is a symptom of dehydration and is a signal to replenish body water. However, this also means that by the time thirst occurs, our body water is already slightly depleted. This probably is not that big a deal for most of us; however, to an athlete engaged in competition, this can result in decreased performance and the difference between victory and defeat. Most athletes who compete in endurance sports will drink prior to and during an event. A common belief among endurance athletes is that they should need to drink before we are thirsty.
Can dehydration affect sport performance?
By the time we have lost about 2 percent of our body weight as water we will become thirsty and may experience a slight reduction in strength. By the time we are dehydrated by 4 percent of our body weight, muscular strength and endurance are significantly hindered, while a 10 percent reduction of our body weight as water is associated with heat intolerance and general weakness. If dehydration continues, life itself becomes threatened. If dehydration continues to a 20 percent loss in our body weight, we become susceptible to coma and death. We will discuss the need for proper hydration in the Chapter 11.
Highlight: Is water our most essential nutrient?
Many people regard water as our most important essential nutrient. This is because of three principal concepts. First, when we do the math, our dietary need for water far exceeds any other essential nutrient. For instance, 1 mL of water weighs exactly 1 g, therefore daily need for water for an adult would be approximately 2,000 to 3,000 g (2 to 3 kg). This is about 30 to 60 times greater than our need for protein and millions of times greater than our need for different vitamins and minerals.
Second, signs and symptoms of water deficiency begin to show much more rapidly than any other essential nutrient. If we abstain from all food and drink, we would develop signs of water deprivation by the end of the first day or two. Furthermore, we may die from severe dehydration by the week’s end.
Third, as water is the basis of the human body, water imbalance (dehydration or toxicity) could not occur without influencing the metabolism of all other nutrients in some way.