What causes diarrhea in children?

Here’s another excerpt from my new book, How Your Child Heals. It’s from the chapter on symptoms, and it’s about what causes diarrhea.

Diarrhea, the frequent passage of watery stools, is something with which most parents of small children are well acquainted. It is a common symptom because its most common causes, intestinal viruses, are all around us. There are many of these for a child’s immune system to meet as it matures. Each new encounter usually causes illness, but subsequent exposures often cause few or no problems. These viruses are highly infectious, so they spread easily wherever toddlers gather to share toys and cookies. The result is what doctors call gastroenteritis, a fancy term for an inflamed stomach and intestines.

Other things besides viruses can cause diarrhea, but most of these cause it in the same way intestinal viruses do — injuring the cells lining the intestines so they cannot do their job of absorbing the nutrients passing by them. A wide variety of food intolerances can also lead to diarrhea, often because the absorbing cells, though present in the intestine, are in some individuals unable to deal with a particular food properly. Common examples of this include a deficiency of the absorbing cells that process lactose, a type of sugar in dairy products, or a sensitivity to the proteins present in cow’s milk. Whatever the cause of the poor functioning of the absorbing cell lining, the result is often diarrhea. If there is significant stretching and squeezing going on in the intestine the child will often have cramping pain, too.

When the intestinal lining is injured, it cannot do its job of absorbing food. If a large amount of unabsorbed food makes it to the lower reaches of the small intestine, it draws water out of the intestinal wall. It also becomes excellent food for all the bacteria living there, and the action of the germs gorging themselves on this sudden feast produces even more substances that draw water into the intestine. When this mixture is dumped into the large intestine, the enormous mass of bacteria normally living there magnifies the effect. The large intestine can absorb quite a bit of water, but it can become overwhelmed by the volume of what it is being asked to take in. Plus, its lining cells may themselves be injured by the infection and be less able to do their job.

These things makes the stools watery. Diarrhea also means more frequent stools. The simple increase in the amount of material the intestines must deal with is one cause of the more frequent stools. Another is that most causes of diarrhea also speed up the transit time, the length of time it takes what a child swallows to pass all the way through.

There is another kind of diarrhea, one less common in children. This disorder is of the large intestine, the colon, and is called colitis because that word means an inflamed colon. It is typically caused by one of several varieties of infectious bacteria. Since the colon can become quite irritated and inflamed, the diarrhea of colitis often has blood in it from oozing off the intestinal wall. It is usually a more serious illness than simple gastroenteritis of the upper reaches of the intestine. This is why seeing blood in your child’s stools is a reason to visit or call the doctor, especially if your child has fever as well.

We have several ways to deal with diarrhea, the first of which is to do nothing other than make sure your child is getting enough fluid to replace that lost in the stools. This is how doctors usually handle the situation, because typical gastroenteritis is quite self-limited and will pass soon. When it does, the damaged absorbing cells very rapidly replace themselves on the villi and all is well. If it persists for many days, that is a reason to suspect something else is causing it.

Simple common sense teaches us we should not challenge the intestines of a child with diarrhea with large meals full of complex, difficult to absorb foods, because the poorer the absorption, the worse the diarrhea potential. Parents have known this for generations. This is the rationale for using smaller, more frequent meals of simple starches like rice and bread, or even of eliminating all solids for a day or so. There are several ways of approaching this issue, but many parents find out by trial and error which dietary manipulations work for their children and which ones do not.

We do have several drugs to treat diarrhea, most of which work by slowing down the transit time through the intestines. Lomotil is the brand-name of a commonly used one. These drugs affect the intestinal nerves that control how fast the intestines squeeze the food along, slowing down the process. They work well in adults, although you can easily see how it is possible to overshoot and end up with constipation. However, doctors rarely recommend these drugs for small children because, as with the nausea and vomiting medicines, the potential side effects outweigh any benefit of using them for a condition that usually quickly passes without treatment.