12.5: Water and the Body’s Wastes

Except for the breathing out of carbon dioxide, most of the waste products of body chemistry are discarded through urine and feces. Urine is clearly a watery instrument of waste disposal. The kidneys use rather large amounts of water to carry off waste products which they have removed from the blood.

The amount of water needed—and thus the volume of urine—becomes larger when a lot of waste must be disposed of through the urine. For example, excess salt intake increases the amount of urine. When we eat a lot of salty foods (table salt = sodium chloride), more water is needed to get rid of the excess sodium. Beer joints don’t lose money on free bowls of salty peanuts, pretzels, or tortilla chips. We feel thirsty, drink more, and urinate more.

Sea water has so much salt that the kidneys need additional plain water just to dispose of it. So, ironically, when castaways drink sea water because of desperate thirst, they actually cause their bodies to become dehydrated faster.

When blood-glucose is abnormally high (as in diabetes), glucose is excreted in the urine (urine is normally glucose-free). This results in more water loss and thirst. The first symptom of diabetes is often increased urination and thirst.

Feces, the “solid” wastes of the body, also carry a fair amount of water. In fact, we might recall that dietary fiber does much of its work in speeding up “transit time” in the colon by holding water, making the stool softer and bulkier. The more fiber in our food, the more water carried by the feces.

But we should keep in mind that when the colon moves its contents through too fast, the colon doesn’t have time to absorb all the water it should, and the result is diarrhea. Diarrhea can cause rapid loss of body water. The water loss from some diarrheal diseases can be life-threatening.

Dehydration resulting from severe diarrhea is a leading cause of infant death in developing countries. In these countries, infant diarrhea is commonly due to ingestion of disease-producing bacteria, often from fecal contamination of drinking water. As one might expect, an acute response to ingesting toxins, including disease-causing bacteria, is vomiting and diarrhea.

---

In developing countries, a mother’s use of clean water with a bit of added sugar and salt to feed her infant (oral rehydration therapy) has rescued many an infant from fatal dehydration from severe diarrhea. The sugar and salt speed the absorption of water and provide a little nutrition.

---

In the extreme situation of cholera, for example, there’s severe diarrhea. The cholera bacteria make a toxin that causes water to actually be drawn out of the tissues into the intestine. In addition, there’s vomiting, which causes more loss of water and electrolytes. In the most severe cases, several quarts of body water are lost within a few hours. Treatment calls for the immediate administration of intravenous fluids. Untreated, the fatality rate from severe cholera is over 50%.

Ridding the Body of “Toxic Wastes”

Many popular diet-and-health books promote regimens for “ridding the body of toxins and toxic wastes.” But these books define “toxins” and “toxic” rather vaguely. For good reason. The line between toxins and non-toxins isn’t always sharp. Even essential nutrients or plain carbon dioxide can be toxic in excess, and toxins in small amounts can be harmless. The body has its own regimens for ridding itself of toxins—regimens far more sophisticated than those devised by such dietary manipulations.

Vomiting and diarrhea are, of course, the body’s most violent response to toxins in our food and drink. But what of bodily “toxins”?

The body routinely gets rid of the “toxins” it produces. If this weren’t so, we’d all soon be poisoned to death. Think of those whose kidneys don’t function as they should in ridding the body of “toxic wastes.” Modern medicine keeps them alive by “detoxifying” their blood through dialysis.

---

To maintain water balance, your body regulates fluid intake and output.

---