Why Is Water the Most Important Nutrient?

Water constitutes 55-60 % of the body’s weight. Interestingly, we can go weeks without eating adequate calories, vitamins, and minerals, but only a few days without water. From athletes to the average individual, most people wonder how much water is needed. Although there are several methods for estimating fluid needs, there is not a one size fits all.

The Ins and Outs of Water

We ingest water in only 2ways (excluding IV fluids). The water in our body comes from the beverages and food consumed. Whereas fluid losses can be contributed directly to urine losses (which are measurable) and insensible losses (not easily measured) such as respiration losses (think of blowing on a cold window and watching the condensation collect), perspiration, and water lost in stool output. These insensible losses account for about 1/3 of the total fluid output.

What’s water do anyway??

Water has many functions in the body. The functions include: being a solvent for the biochemical reactions that take place in the body, maintaining acid and base balance (pH) in the body, releasing calories or energy from the foods consumed in the diet, regulation of body temperature, and growth of new tissue.

The body controls the amount of water that is retained or excreted depending on the concentrations of electrolytes, particularly salt.

How Much Water Do I Need?

There are several ways of calculating water needs in the body. One of the simplest calculations is using 1 ml/calorie consumed. This is fairly simple if you know that 30 ml=1 fluid ounce. So let’s look at an example of a person consuming 2000 calories/day (to meet their estimated energy expenditure). Based on the formula of 1 ml/calorie consumed, we could evaluate that this person needs 2000 ml/d. Most Americans however are more comfortable using ounces, so we must do a tiny bit of mathematical conversion as follows:

2000ml = 66.6 ounces AND 66.6 ounces = 8.2 cups water/day

30 ml/oz 8 ounces/cup

So, we see where the 8 cups of water per day rule comes into play. However, water needs can sometimes be more, particularly if you are exercising, traveling, visiting a higher elevation, living/working in a hot environment, or having a bout of diarrhea. More fluid is needed during exercise and in a hot environment primarily because of increased perspiration or sweating. Flying on an airplane or visiting a higher elevation can increase respiratory water losses. In fact, for every hour of air flight, 2 cups of water is lost! And the water loss from increased stool output can also be significant.

One of the best rules of thumb for monitoring hydration levels is to observe your urine output and color. When adequately hydrated, urine color should be light yellow and frequent (ever 2-3 hours). Dehydration will result in dark yellow to brown, concentrated urine in small amounts that occur infrequently. Over hydration is seen with large amounts of clear urine occurring often. Both dehydration and over hydration can be significant and detrimental.

Help! I’m Parched!

Dehydration occurs when there is inadequate fluid intake, often combined with increased fluid expenditure such as sweating or from increased elevation. Symptoms of dehydration often appear similar to other symptoms and may be missed even by a health care professional if a complete history is not taken. It is important to remember that the average human body is 55-60% water and the body become symptomatic with even small fluctuations and signals the brain to try to correct the imbalances. The table below describes the symptoms associate with the negative percentage change of the body’s water weight:

Homeostasis (The body is 55-60% water)	No symptoms
1-2% Loss	Thirst becomes increased
4% Loss	Muscles lose strength and endurance, fatigue
10-12% Loss	Heat intolerance, increase core temperature, weakness
20% loss	Coma and Death

It is always surprising to hear of someone that dies of dehydration. How could this happen? It happens because human beings are the only mammal to ignore their own thirst. For example, let’s look at the family dog. Let’s pretend that the dog’s water bowl has been depleted and not refilled. The dog is thirsty. But the dog is unable to verbalize to his owner that he is thirsty and becoming dehydrated. The dog will seek out alternatives, such as drinking from the toilet.

Human beings on the other hand, are very good at ignoring body cues, particularly thirst. Let’s look at another example of a sixteen year old boy. The boy is playing his first year of high school varsity football. It is August in Texas. The heat and the practice are both more intense than the boy has anticipated. He is thirsty, but the coach has already announced that water breaks will only be allowed at his discretion. The boy continues to ignore his thirst. Soon his body is moving slower and with less power. If the player does not rehydrate soon, his core temperature will continue to increase, causing heat intolerance, and full body weakness. After the 20% loss, the player will be comatose or dead. It becomes imperative to respond to thirst and drink until that thirst is quenched, particularly in these types of conditions.

My Cup Floweth Over…

Over hydration can be just as critical of a situation. However, most of us don’t think of this being too big of an issue and thankfully it is not, except in certain specialized populations. Over hydration is also known as water intoxication. When too much fluid is consumed in a short period, it can overwhelm the kidneys, even fill the lungs, and cause a severe sodium balance called hyponatremia, which literally means low salt in the blood.

Hyponatremia implies that there is too little salt in the blood, but this would be a misnomer. Imagine three equal size clear containers (that represent the human body). Each container is filled with 9 particles of sodium chloride (table salt). One container is filled half way and this first container represents normal hydration. There is an adequate amount of sodium in the body, not too much or too little. In the next container, the same 9 particles of sodium are present, but this time, the container is only filled ¼ of the way. Here we have the same amount of salt, but it is more concentrated because it has less water or fluid. This represents dehydration or the condition known as hypernatremia. This does not mean that too much salt has been consumed, there are still 9 particles of salt in the solution. Instead, there is simply not enough fluid. Finally, in the last container, the same 9 particles of salt are present. This time, the container is filled to the brim. This solution is very diluted. It does not mean that the individual is salt deficient, but that there is too much fluid in the body, creating the condition hyponatremia.

Back to the original question…who is at risk for “over filling their container”? In reviewing popular periodicals, newspapers, and journal articles, there are a couple of groups that stand out. The first is marathon/endurance athletes. Many of these athletes, even elite or highly trained nonprofessional athletes, such as Boston marathoners have fallen victim of the fluid trap. Why? They are afraid that they will become dehydrated so they drink extra fluid to try to offset their anticipated losses, and end up drinking too much. In addition, they don’t want to stop and use the bathroom as this might increase their finish time, so they hold it. Extremely thin runners are at a higher risk because of limited fluid volume in the body. In one study from the New England Journal of Medicine, some 488 Boston Marathoners were measured, weighed, and labs drawn pre and post race. Researchers found that 1 in 8 had serious fluid and salt imbalances. They found that in this population, some runners gained between 4.5 to 11 pounds from drinking water along the route. (For those not familiar with the marathon, it is 26.2 miles). To give you an idea of what it would fill like to “carry” that much fluid, imagine running with a gallon of milk (approximately 7 pound of fluid)!

Another group that was reported by The Dallas Morning News to have been overhydrated were fraternity students involved in a hazing incident at Southern Methodist University. According to reports, these students of Alpha Phi Alpha fraternity were forced to drink hot sauce, followed by gallons of water, and then struck by wooden paddles at an off campus apartment. After the students were found to be unconscious, the men tried to get them to vomit. Medical personal found them to be severely overhydrated, demonstrated by hyponatremia and pulmonary edema (water in the lungs).

Lastly, another reported group to have some self-induced over hydration were contestants on a radio game show trying to win a game system. They were forced to drink and not urinate. The outcome resulted in kidney failure and death.

Obviously, drinking is important in adequate and balanced amounts. Again, fluid intake should be dispersed throughout the day. More fluid may be needed during special times such as exercising in a hot environment, but it also important to be aware of the risks of over hydration and equally important to pay attention to urination cues.

Hydration is vital to maintaining optimal health and performance. For the an individualized nutrition assessment, including fluid requirements, contact Leslie Goudarzi, MS, RD, LD, Wellness Dietitian at Good Shepherd Medical Center’s Institute for Healthy Living at 903-239-1551.