What causes constipation?

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You have been particularly irritable over the past two days. Your belly hurts, your body aches, your appetite is all over the place, and you are unusually gassy. What’s going on? You take a brief personal moment for introspection and it occurs to you that you have not pooped in 56 days. Could this be the source of your daily woes? It certainly could.

Constipation is one of the most common medical problems in existence, affecting almost every person on the planet at one point in time. Constipation has been noted in 2000-year old Egyptian mummies. In more modern times, constipation has been documented in Kings, Queens, firemen, butchers, plumbers, mail carriers, rock stars, and even nomadic llama herders.

So what causes this intestinal scourge? While many people think there must be a glamorous explanation, such as thyroid disease or a major mechanical malfunction, the majority of cases are simply caused by temporary slowing of the bowel after a mild illness. Most infections only last a few days, but constipation, once it sets in, really likes to stick around.

To explain constipation’s stubborn resilience, it helps to understand some basic nuts and bolts of the colon and rectum. Let’s take one of the most effective intestinal transit time measuring devices, a peanut. For those of you following along at home, you could also use a kernel of corn, if no peanut is available. A swallowed peanut takes less than 10 seconds to travel through the esophagus to the stomach. It exits the stomach within about 4 hours and traverses the small intestines in less than 2 hours. In the colon, things slow down a bit. It typically takes 12 to 24 hours for an object to move around the colon and drop into the rectum. Once the rectum has filled with just the right amount of poop, and there is a toilet conveniently nearby, the rectum will empty.

Let’s do an experiment. Here we have Charlie. First we will watch as Charlie eats a cheeseburger. As you can see, the cheeseburger travels casually through the stomach and intestines and begins packing leftover cheeseburger debris into the rectum. If all is chugging along normally, the rectum should fill over 12 to 24 hours and will send Charlie a signal just as one day’s worth of soft poop finishes filling the rectum. Charlie, in an attempt to keep his rectum happy, makes a casual trip to the restroom.

But, just for fun, let’s give Charlie some constipation. The stomach and intestines may slow down a bit, but the primary change is that the rectum becomes extremely lazy. Sleeping on the job, the rectum fails to send the empty signal until several days later. Meanwhile, the colon’s job in life is to remove water from poop, and it doesn’t know when to stop removing water. So, by the time the rectum decides to send

the “empty me” signal to Charlie, the poop in the rectum is large, hard, and painful to pass.

There are two major classes of constipation medicines: osmotic agents and stimulants. Osmotic agents (like fiber, prune juice, and MiraLAX) hold onto water to keep the poop soft. Stimulant medications rev up the bowel wall in an effort to push the poop out more quickly and forcefully. You should discuss treatment options with your doctor.

In the meantime, a diet high in fiber, regular toilet sitting times, and adequate oral fluids can help prevent constipation and will keep you rectum happy.

Michael K. Davis, MD
The Impatient Doctor

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