Understanding How We Eat by Mouth: Notes from the Front Lines of Eating Support (4)

Written by: 五島 朋幸 (Dentist)

Eating by mouth is something we take for granted. We learned to do it as small children without really thinking about it, and it doesn’t seem like a particularly difficult movement.

You probably know that society is aging, but did you know that we now live in a world where people can survive even after they can no longer eat by mouth?

As animals, we cannot live without taking in nutrition of some kind. In other words, in the past, losing the ability to eat by mouth meant death.

Thanks to advances in medicine, however, people can now live even when eating by mouth is difficult. Take gastrostomy, for example: by making an opening into the stomach, passing a tube through it and delivering nutrition directly through the tube, people can live without eating.

Medical progress sometimes brings troublesome problems with it. It has created a state in which people can live without eating by mouth. I don’t mean to say that everyone in this state is merely “being kept alive.” But the question remains: can a state in which someone has almost no consciousness and is kept alive by a gastrostomy tube be called “living”?

Precisely because we live in such times, let’s think again about eating by mouth, and about living. In this column, I’ll start by breaking down the act of eating by mouth into its parts.

Recognizing food

First, there is food in front of you. Before anything else, you must recognize that it is food, not a plate or a piece of stationery.

In front of you is a bowl filled with white rice. Of course you know it is rice. But if you set a rice bowl down in front of someone from a country with a completely different culture who had never seen a rice bowl or rice, what would they do?

They would probably sniff it and touch it with their fingers. They might even nibble or lick the bowl. Then they would cautiously put some rice in their mouth, and only then realize it is something they can eat.

When a meal is laid out on the table, we instantly recognize it as food. That is why we put it in our mouths.

In fact, the opposite also happens. People with symptoms of dementia (especially Alzheimer’s disease) may fail to recognize food as food and not put it in their mouths, or may scrape at the pattern on a rice bowl with chopsticks, trying to eat it.

You too might mistakenly put a realistic plastic food sample in your mouth. That would mean you had judged, from the visual information you have gathered over the years, that “this is food!”

The first step in eating by mouth is recognizing that something is food.

The tongue is key to chewing

When food goes into the mouth, a small amount goes straight in, but if a piece is large, we bite it off with our front teeth.

In dentistry, the front teeth are the first three teeth counting from the center on each side, top and bottom: the canines (often called “eye teeth”) and the teeth in front of them.

As you may have noticed, front teeth and back teeth have different shapes. This is because they have different roles: front teeth are shaped for biting off, and back teeth for grinding.

Once food is in the mouth, all that’s left is to chew, right? Not quite. First, the food has to be placed on top of the back teeth. That is the tongue’s job.

The lower jaw moves up and down and a little from side to side, but it is the tongue that controls food and moves it around in the mouth. As the jaw moves, the tongue moves in step with it, keeping the food positioned on the back teeth. At the same time, working with the cheeks, it keeps the food from falling off the teeth.

The tongue’s work is truly important; if its movement or strength weakens, a person may become unable to chew solid food.

So what is the purpose of chewing? Actually, the goal is not simply to make food smaller or softer. The goal is to turn food into a form that can be swallowed. Think of this as a state that is not just soft but also holds together to some extent.

It is quicker to try it yourself than to have it explained. Put something in your mouth and chew it: the state it is in just before you swallow is the “swallowable form.”

Swallowing is an “intersection”

Once chewing has turned food into a swallowable form, it is sent from the mouth to the throat.

It would be fine if it then simply flowed on into the esophagus, but there is a big problem here. The throat, through which food passes, leads into two passages. One, of course, is the esophagus, the entrance to the stomach and intestines. The other is the windpipe (trachea), which we use for breathing.

You have probably experienced it: when you eat in a hurry or someone speaks to you at the wrong moment, food goes into the windpipe and you cough and splutter. At an intersection, there are no accidents as long as the traffic lights work properly and drivers obey them, but accidents happen when someone brakes too late or speeds through on yellow. Swallowing works the same way.

In fact, the entrances to the esophagus and the windpipe are not both open all the time. Normally only the entrance to the windpipe is open, and the entrance to the esophagus is collapsed shut. In other words, when we are not eating or drinking, the throat serves as a passage for breathing.

When we eat or drink and food enters the throat, two movements occur:

• The entrance to the esophagus opens wide

• A lid closes over the windpipe

This protects the airway so that food goes into the esophagus rather than the windpipe. It is a clever design, isn’t it?

But if the esophagus doesn’t open well, or the lid closes too slowly, food flows toward the windpipe. This is called aspiration, and a disorder in which this happens is called dysphagia (a swallowing disorder).

Summary

What did you think? I hope you can see that eating, something we do every day without thinking, is actually a sequence of very complex movements.

Put the other way around, there is no single cause of being unable to eat by mouth. If the cause is correctly identified and appropriate care is provided, a person can sometimes eat by mouth again.

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About the author: 五島 朋幸 (Dentist)

Born in Hiroshima in 1965. Graduated from the School of Dentistry at The Nippon Dental University in 1991 and began providing home-visit dental care in 1997. Head of Fureai Shika Goto (Fureai Dental Clinic Goto) since 2003. PhD in dentistry. His roles have included clinical associate professor in the Department of Oral Rehabilitation at The Nippon Dental University Hospital, lecturer in the Department of Dental Hygiene at The Nippon Dental University College at Tokyo, and part-time lecturer at Tokyo Medical and Dental University. Representative of the Shinjuku Eating Support Study Group. Since 2003, he has hosted the radio program “Doctor Goto’s Passionate Home-Visit Clinic.” His books (in Japanese) include Oral Care: Dos and Don’ts (Chuohoki Publishing) and Home-Visit Dentist Doctor Goto 1: The Dentist Comes to Your Home! (Osumi Shoten). (Profile as of the time of writing.)

This article is a contribution from a medical or care professional, re-edited by our editorial team. It provides general information as of the time of writing, and symptoms and circumstances differ from person to person. For specific decisions, please consult your doctor, dentist, pharmacist or another professional.

This is an English translation of a column originally published in Japanese by Next Co., Ltd.

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