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Episode 57: How Digestion Works (And Why You Should Care)

Episode 57: How Digestion Works (And Why You Should Care)

If you had to explain digestion to someone, where would you start? Digestion is arguably the most important system in the body and yet, few people actually know what's happening from top to bottom.

On this short, bite-sized episode, nutritional therapy practitioner Andrea Wien, breaks digestion down in an easy-to-understand way that will give you an appreciation for the marvels your body undergoes at every meal.

Along with describing how digestion is supposed to work, she also gets into what can go wrong and why you may be experiencing uncomfortable symptoms like gas, bloating and constipation.  Follow along during the episode with the infographic below. 

how digestion works

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ultimate gut health guide


Andrea Wien: Welcome to The Microbiome Report powered by BIOHM Health. I'm your host, Andrea Wien. And we are doing something a little bit different today. We're starting to add a few more episodes each month, which is so exciting for all of us here at BIOHM. And we hope that you will enjoy them too. But we're going to start doing these bite sized episodes. And what that means is I'm going to come on, I'm going to talk about some things that I go through with my clients in sessions sometimes, or just questions that we've had. And some of these may be related to digestion, but some of them may be a broader scale. For example, what makes up a healthy versus an unhealthy fat? Or what does vitamin D really do in the body? And is it that important to continue to take it as a supplement? Should everyone be taking it as a supplement?

So these are the types of questions that we are going to get into. And today I wanted to start these off with look at how digestion works. So this is something that I go through with every single client that walks through my door. And I'm always really shocked at how many people don't really understand the mechanics of what's happening. We talk about gut health, we talk about digestion, we talk about how it's such an important process. In my opinion, maybe the most important process of the entire body. And so many people don't know how it works. So I have a really great infographic that I share with all of my clients and I walk them through it step-by-step. So I'm going to walk through this infographic and I'm going to put it up on our show notes page at, under this episode.

So please, if you can, right now, go open that page, pull up this infographic, and it'll just make a lot more sense as we're walking through it. If you can't, no worries. These episodes are bite sized, so you can certainly come back, give this 10 minute episode a listen and follow along at that point. Like I just said, I love this infographic, but the one part that I don't agree with is number one, it says digestion begins as soon as food enters your mouth. Now, that's actually not true. Digestion begins in the brain and in the vagus nerve before we ever take our first bite. This is something called the cephalic phase of digestion. And that sounds a little bit fancy and science-y. But if you've ever thought about food, or right now, if you picture biting into a lemon, that feeling that you get of salivation at the back of your salivary glands in your mouth.

When you start thinking about food that's really yummy and you can't wait to eat it and your body starts sending that message... Your brain, I'm sorry, starts sending that message to the rest of your body that food is on the way. That's actually priming your system for digestion. Digestion begins in the brain before we ever, ever take our first bite. Now, why is that important? We can kind of talk through as we go through this how digestion is supposed to work and how it works when maybe things are dysfunctional. So if we're not taking a moment to really look at our food, sit down at a table, all of the eating hygiene that we talk about, taking a couple deep belly breaths, enjoying the food that you're eating, that message is never getting started in the brain. So if we're just grabbing a granola bar, jumping in the car, yelling at the kids on the way out, our body is not primed to be eating.

It's not in a state to be eating. So this cephalic phase of digestion is really critical for making sure that the rest of the stages go according to plan. Now, like I said, this can be something as simple as taking a few deep belly breaths, really looking at your food before you eat it and getting excited about eating it. That can all really trigger that stage of cephalic digestion. Okay. So now we put that first bite into our mouth. If you watch people at a restaurant, this is a fun trick. And I know right now, not many people are going out to restaurants with COVID. But maybe just watch your partner, or watch your kids or someone who is close by to you and see how many times they're chewing. On average, people chew two, maybe three times before they're swallowing. And this is really doing the body such a disservice, because the mouth is one of the main places where mechanical digestion is happening.

Now, when we talk about mechanical digestion versus something more like enzymatic digestion, right? Mechanical digestion is the actual chewing motion. So in your mouth is one place that it happens. And another part where mechanical digestion happens is in the stomach, where your stomach is churning, and squeezing, and actually acting more like a little valve in there that's moving the food along. So those are your two main forms of mechanical digestion. And if we're not chewing well enough, we're missing out on a huge step. And we're putting a lot more pressure on the rest of the body, the stomach, the large intestine, small intestine, pancreatic enzymes, everything has to work way harder if we're not showing well enough. How do you know if you're doing well enough? If your food is not the texture of a peanut butter, you're not doing well enough.

It kind of sounds a little bit gross, but you really want to slow your process down. Make sure you're chewing. Sometimes this looks like 20-30 bites. So it can be a little bit of a learning curve as we're starting to do this. I tell people, put your fork down between bites, take a couple breaths between bites. It feels like you're eating so slowly, but that's what we want in this phase. Now, also you have some enzymatic digestion happening in the mouth with your saliva. So your saliva starts mixing with those food particles and breaking them down as you chew. And here on our infographic, if you're following along, what is an enzyme? Enzymes are protein-based substances that play an important role in every function in the human body, not just digestion. So they're really things that are building up or breaking down the particles that we're ingesting.

As we move further down, we go down the esophagus. We hit right before we get to the stomach, something called the lower esophageal sphincter. Also called the LES. This is a muscle, or group of muscles, that prevents stomach acid from coming back up into the esophagus. Now, the interesting thing about this little valve, this little sphincter, is that it's fairly weak when it gets pushed up on. It's really only supposed to open going down, as food is going down into the stomach. Now, anyone who has had acid reflux or any type of GERD, that sphincter is malfunctioning. There's a number of reasons why that can happen. One of the main ones is that we didn't chew well enough. The cephalic phase didn't kick in, we're eating on the go, and our body was not primed for digestion. So suddenly the food gets into the stomach and instead of digesting, it starts rotting, and putrefying, and fermenting and gases build up.

If you think about if you've ever made sauerkraut, or kimchi, or opened a jar that is under that type of pressure, there's a lot of pressure there. Open a soda is a great example even. If you've ever shaken a can of soda and then opened it right away, it explodes. Well, the same thing is happening in our stomach. This is a chamber, an enclosed chamber, and when we have food in there that's not being properly digested, gases are building up, and then those are pushing up against that lower esophageal sphincter, and the stomach acid is getting into our esophagus. So that's that feeling of heartburn that we feel. Now in a minute, we're going to talk about hydrochloric acid and how a lot of times... Actually, let's just jump right in and talk about it now. That sphincter opens, the food goes into the stomach, and hydrochloric acid is the juice, the acid that's in there and breaking down all of the things that we've eaten.

Now, there's a few ways that hydrochloric acid gets triggered. The first one, coming back to that cephalic phase of digestion in the brain. There's also some nutrients that we need, B12, and zinc, and a few other things that build hydrochloric acid. And the interesting thing is people who have any type of GERD or acid reflux often are told they have too much stomach acid. The case 90% of the time is that people actually have too little stomach acid. So you might be thinking, well, how does that make sense? How is that acid getting up into my esophagus if I have too little? Well, we just talked about how that food is rotting and putrefying and all of those things in the gut. And it's building up all of that pressure and that pressure is pushing on the esophageal sphincter. There's not enough hydrochloric acid to actually break that food down.

And what little hydrochloric acid is in there is splashing up. So a lot of times the PEPCID, Zantac, all of those types of medications of the world are just decreasing the stomach acid, which of course is helping that feeling. But is doing long-term damage in the long run. We don't want to be preventing the hydrochloric acid from producing. It's actually a critical part of digestion. And we'll see even more in the next phase, why it's so important. But if you are having those types of symptoms, I really urge you to work with a functional nutritionist or a functional doctor who can help you get off of those medications, because it can be really uncomfortable if you've been using those, and then you suddenly stop and want to increase your hydrochloric acid production. So you probably can't do it alone. There are some tips and tricks that we could talk about. But for now, just know that 90% of cases of acid reflux are actually too little stomach acid.

Moving on to the next phase where the food enters into the small intestine. What triggers that move from the stomach into the small intestine, is the acidity of the contents of the stomach. So again, if we don't have enough hydrochloric acid, we don't really send the message to the body, "Hey, open that next valve and send everything to the small intestine." The stomach wants to hold onto it. It wants to keep digesting it. But eventually, maybe we eat another meal, the stomach is... While it can hold up to a quart of food, is not an endless supply of space. So eventually that food has to move on whether or not it has reached that level of acidity that should open that door. You can think of it as the key that's opening the door to the small intestine. So let's say that the food doesn't have enough hydrochloric acid as it moves into the small intestine.

The problem with that is not only now do we have larger pieces of food that are undigested, but hydrochloric acid is what we need to trigger the release of enzymes from the pancreas and trigger the release of bile from the liver and gallbladder. The pancreatic enzymes are things like amylase, protease, lipase. You may have seen these if you've ever taken a digestive enzyme. But these are the things that are helping to digest carbohydrates and proteins and fats. Whereas, bile, you can think of this more as the dish detergent in your gut. So if you've ever tried to wash a dish that has some grease on it and you don't use soap, it doesn't really go very well. It kind of just mixes it all around and you're still left with it on the plate. The bile is really that dish detergent that comes in and breaks down the fat in the small intestine.

But again, none of these processes are triggered unless we have adequate hydrochloric acid coming from the stomach. Once we have the food into the small intestine, most of the nutrients are going to be absorbed and digested here. When we talk about leaky gut, this is also where we talk about that in the small intestine. We can get into that on another episode of one of these, and I'll get into more detail on exactly what leaky gut is and how that undigested food might cause issues when we're talking about the small intestine. But let's say everything is going according to plan, the small intestine food moves through and gets to the large intestine. Now, depending on what type of food we're eating, this can take anywhere from 30 minutes up to five hours, let's say. Sometimes things move faster. Sometimes things move slower. And also those are all signs that maybe there's something going on.

If foods moving too quickly through the small intestine and the colon, also called the large intestine, we see diarrhea, maybe some cramping. And if things are moving too slow, that's when we start to see backup and constipation. After the food gets through the small intestine, it enters the large intestine. And this is really where we start to see and talk about the microbiome. The majority of the bacteria, fungi, viruses, organisms, that we talk about when we talk about microbiome health, all reside in this large intestine area. This is really where the body is going to start getting things ready to be evacuated. Where all of those metabolites, those byproducts of the microbes come into play. They get reabsorbed back into the body as things like B vitamins or butyrate. Some of these end stage products that are really helpful for the body's functioning.

This is also where the leftover waste gets kicked out to the liver and the kidneys. And this is where fiber really comes into play. So when we're talking about fiber, soluble fiber and insoluble fiber, which we won't get into, we did an entire episode if you're interested in the differences in those, and how to know if you're getting enough fiber into your diet and the right kinds. We did an episode with Meghan Telpner, so please go back and check that out. But this is really where everything is prepping to be eliminated from the body. And that's the stages of digestion.

So, as I mentioned, I will link to this on the show notes page at And if you have a topic that you've always wondered about, or you want me to get into and riff on a little bit in one of these episodes, please shoot me an email or find me on Instagram. I'm @Dreeats there. Or our email is As always, thank you so much for listening. I'm Andrea Wien, and we will catch you next time.


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