Digestion for (not-so) Dummies: The Mouth

All aboard!

Yes, folks, it’s that time again: time for another stop along the route of the digestion train. You’ll recall that last time we departed from the brain’s station, so today we’re scheduled to arrive right on time at the mouth. (Digestion is a north to south process, remember?) The mouth is probably the most underappreciated part of the GI tract, which is hard to believe, considering it’s the very first place where any actual digestion occurs. With that in mind, it should be obvious that what happens in the mouth sets the stage for the entire rest of the digestive cascade. So in case you thought your mouth did its best work over the phone (or perhaps in the bedroom, but we won’t go there ‘cuz this is a family show), keep reading. It’s time to stop underestimating the importance of the mouth in digestion.

The two key things that happen in the mouth to get digestion started are chewing and insalivation. They’re pretty closely related, as I’m sure you can imagine, thanks to many years of firsthand experience with both of those. After all, you've been eating solid foods for...well, a few years by now, I would hope. And these two key things get the party started on two really key things: the mechanical and chemical breakdown of food.

Let’s talk mechanical first. Mechanical breakdown just means the physical act of chewing—breaking down bites of food into smaller pieces. This is important for a few reasons. First, the more we chew, the smaller the individual bits of food become. And the smaller the individual bits are when they reach the stomach, the more surface area there is for stomach acid (also known as hydrochloric acid or HCl) to come into contact with the food and do its job of breaking down proteins. Think of it this way: chewing well gives the stomach a bit of a head start and eases its burden a little. (The stomach continues the mechanical breakdown of food, so the better a job you do of it in your mouth, the less your stomach has to take care of.) Second, the more we chew, the more we allow salivary enzymes to mix with the food and begin the chemical breakdown of food. So let’s talk chemical breakdown next.

We’ve all heard of stomach acid and digestive enzymes, but I’m guessing that unless you remember your high school biology, you might have forgotten that there are salivary enzymes that start digesting food right here in the mouth. There’s salivary amylase, which works on carbohydrates, and also a tiny bit of lingual lipase, which works on fats. For our purposes though, it’s enough to know that carbohydrates start getting transformed in the mouth, and there’s very little fat or protein digestion happening up there. (You can do a little experiment at home to confirm this about carbs: take a saltine-type cracker or piece of white bread [if you have one…but why would you?] and let it get nice & wet with saliva. First, you’ll discover that you don’t even have to chew because the darn thing is pretty much liquefied. Second, you’ll notice that although the very first taste sensation you likely experienced was savory, after the cracker or bread is mixed well with saliva, that starchy food tastes sweet. So you can clearly see that as high up in the process as the mouth, complex carbohydrates are already being broken down into simple sugars. You could probably also do this same test with a plain, relatively unsweetened cereal, like corn flakes, and definitely with plain, raw, rolled oats.)

Chewing is a lost art, man. We’re all in such a hurry that it seems like we wolf down our food and use a beverage to “help wash it down.” The truth is, we shouldn’t need to drink during our meals. If you chew sufficiently, the food will be mixed well enough with saliva that you don’t require extra liquids to swallow a bite of food. (Unless you’re having something like a PB sandwich, in which case, your mouth will be drier than the Sahara if you don’t take a sip of water once in a while.) When we get to the posts about the stomach, I'll explain a little more about why it's not the best idea to load up on liquids at mealtime. There's more to it than not needing to wash down our food.

If your mouth is as parched as a desert come mealtime, you’re probably not 

drinking enough throughout the day. Stay hydrated before you eat.

One of the instructors in the certification I’m currently enrolled in likes to say that our food should be liquefied before we swallow it. (He says we should drink our foods and chew our beverages.) I’m not sure I agree 100% with that, but there’s no doubt that most of us can—and should—chew a lot longer than we’re used to. My advice is, take a bite of food, chew normally, and when you feel like you’re ready to swallow, chew 10-15 more times. (Seriously, count them.) You will be amazed at how much more the food is broken down. Think of the load being taken off your stomach.

Another reason why chewing sufficiently is so important is that by breaking down the food as much as possible, we’ll end up extracting more nutrients from it. See, we don’t just magically suck up folate and iron because we’ve ingested some spinach. We’ve got to get at the nutrients in the foods we eat, generally by making the food as itty bitty as possible, and breaking it down into its component amino acids, fatty acids, and simple sugars. This is especially important when it comes to plant foods. Human beings do not have the physiology to break down cellulose, which is what makes up the cell walls of plants. (That’s why the fiber in plants passes right through us—we lack the enzyme [cellulase] that breaks it down.)

These white things in our mouths do 

much more than give us pretty smiles.

However, if we were unable to get at those plant nutrients at all -- all that magnesium, manganese, calcium, vitamin C and the rest -- it would be a total waste of time to eat carrots, broccoli, sweet potatoes, eggplant, and other delicious things that grow out of the ground. So we can’t enzymatically digest the cellulose, but we can break apart those cells mechanically, i.e., by chewing. So the more thoroughly you chew plant material, the better chance you stand of extracting vitamins & minerals from it. Those nice, big molars at the back of our mouths aren’t there for decoration, y’know. They’re our best tools for grinding and mashing all that tough-to-chew plant matter. Think about it: haven’t you ever taken a peek at what’s in the toilet after you’ve had a bowel movement? (If not, you should. There are hidden messages in your poop…messages that sometimes scream loud & clear that something is out of balance in your body. More on this a few posts down the line when we get to the large intestine.) If you’ve ever ventured to have a gander, every now and then you’ve probably seen some undigested things in there. Whole kernels of corn come to mind, and also little bits of dark leafy things. Have you ever noticed a piece of salmon? How about chicken? Beef? Probably not. That’s because our stomach acid is exquisitely equipped to properly dispatch protein. It’s the veggies we have a harder time with—no joke! (Especially raw ones! Salads can be healthful, yes, but they are not the end-all-be-all for good nutrition, particularly for someone with weak digestion. Easy to visualize: which is easier to chew very well: a raw carrot, or one that’s been steamed until it’s soft? And remember, chewing is step #1 for good digestion after the brain.)

If you read this account written by a man with an ostomy bag after a jejunostomy, you’ll see why chewing the bejeezus out of your veggies is wise. (A portion of his intestines was removed and he had an external pouch where he could see undigested food and waste material come through.) He explained that he had never seen a recognizable piece of meat pass into that bag—not even when he swallowed whole chunks of steak without chewing—but undigested vegetables were common. (So much for people who claim that meat is difficult for humans to digest and that’s why we should all be vegetarians or some such. No, meat does not “rot in the colon.” *Insert eye roll.* But some of us have an awfully difficult time digesting grains & beans.)

So yeah, the digestive train route is a long one, and I know you want to get to your destination as quickly as possible, but it’s important to stop and spend the requisite amount of time at each station. Step outside, stretch your legs, get some fresh air. Don’t be in such a hurry. Take time to chew and insalivate. (And then take time to chew a couple more times!) Remember what Ferris Bueller said: “Life moves pretty fast. If you don’t stop and look around once in a while, you could miss it.”

Like I said at the beginning: Don’t underestimate the importance of the mouth!

Continue to the next post: Stomach, part 1

Remember: Amy Berger, M.S., is not a physician and Tuit Nutrition, LLC, is not a medical practice. The information contained on this site is not intended to diagnose, treat, cure, or prevent any medical condition.