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  • Writer's pictureThe Med Gym

All About the GI Tract

By Chris Zinn

Do you ever wonder about what happens to your food after you eat it? Where does it go? How do you handle your food once it's in your body?

Most of you probably haven’t given it much thought; for good reason. Once you eat your food, your body is more or less on autopilot to complete the rest. Since we don’t consciously think about what’s going on, we don’t appreciate just how crazy digestion in the body is!

Now if I asked you when digestion in the body started, what might you say?

The stomach? The esophagus? Maybe the mouth?

All good guesses, but none of them are right.

Digestion starts before you are even aware that you’re hungry!

Our digestive system is a complex system made up of many parts, all working together to make sure we get the nutrients we need in our body. Let’s take some time to look at each part, and you’ll see why it’s important to understand how your food choices may affect your digestion, and consequently, how you feel.

The Gastrointestinal Tract

First off, what is the gastrointestinal (GI) tract?

Well, the GI tract is really a lot of things. It’s a 26-foot-long muscular tube that extends from the mouth to the anus and includes everything in between.

It has a variety of jobs that include:

· Processing nutrients

· Detoxifying harmful substances

· Excreting waste

· Helping to regulate the immune system

The Brain

Before the food is dissolved by our stomach acid, or mashed and emulsified by our teeth, we need to actually have food to eat. This means that the brain needs to tell you to get up and find food.

Ever find yourself wandering around the house, and end up in the kitchen opening the fridge and cupboards? Well you might just be bored, or your brain could be telling your body it's hungry and it needs to start “foraging” for food.

Okay, we aren’t quite hunter-gatherers anymore and we don’t have to look around in a field or forest for hours before we find our food, but the concept still applies.

The brain anticipates hunger and sends you searching. While you are looking for pop tarts, your brain tells your mouth to start salivating, and your stomach to start producing digestive enzymes to prepare the body for food.

This is why commercials of foods on TV all day work so well, even though you might not realize it.

The Nervous System

Like I mentioned earlier, most of the digestion occurs without us being aware.

This is due to the autonomic nervous system, which is responsible for controlling our organs without us even paying attention to it.

Even though that sounds a little shady, like some type of malware accessing the information on your computer without your permission. Just imagine if we had to manually control our breathing, or make sure our hearts don’t stop beating.

The autonomic nervous system is broken down into two branches:

The sympathetic nervous system (SNS)

The parasympathetic nervous system (PNS)

Our GI tract responds to both.

The SNS is what we call the “fight or flight” nervous system. You’ve probably heard this term before. All it means is that when something happens to our body, (stress, stimulation, etc.) the SNS activates and shuts down digestive function, our appetite, and food stops moving through the GI tract. The goal is to divert all available energy and resources to get us out of the stressful situation.

The PNS does the opposite, which is why we refer to it as the “rest and digest” system. Its job is to encourage movement through the GI tract.

The Nose

Surprisingly, the nose plays a role in digestion, and being able to properly smell our food is important for a few reasons.

First, smelling our food helps us decide if what we’re about to eat is going to taste good. Bad tasting things tend to smell bad, and good tasting things tend to smell good. It also helps stimulate the appetite.

By the way, this is why having a cold and losing your sense of smell usually affects your appetite.

Second, something called retronasal olfaction occurs when we’re chewing our food. The odor from our food travels down our throat and back up our nasal passageway. These signals tell our body that it’s about to receive nutrients.

The Mouth

Once we put the food into our mouth, we have to chew it.

Humans have teeth that are known as omnivore teeth. Omnivore teeth include teeth that grind, chop, and cut, which allow us to eat both animals and plants.

Our saliva is filled with enzymes that help to soften and breakdown our food, and this happens as we chew, shred, and rip apart the food in our mouth.

The Esophagus

Once we swallow our food, the esophagus carries the chewed food (known as a bolus) to our stomach for further digestion.

The saliva that was used to breakdown our food in our mouth now doubles as a lubricant and helps move the food down the esophagus with the help of gravity, and something called peristalsis. Peristalsis is a series of muscular contractions that occur in a wavelike pattern, that help push the food through the GI tract.

The food then moves through the Lower Esophageal Sphincter (LES), which separates the esophagus from the stomach and prevents stomach juices from splashing or flowing back up into the throat.

The Stomach

Now the fun really begins!

The stomach's job is to churn, mix, and breakdown food into a liquid so that further digestion can occur in the intestines, and larger amounts of nutrients can be absorbed.

Some things can be absorbed in the stomach, such as vitamins, caffeine, and alcohol (which is why drinking alcohol on an empty stomach may lead to becoming intoxicated much more quickly).

The stomach releases gastric juices, such as pepsin and lipase which start the breakdown of protein and fat.

Since stomach acids need to be extremely powerful to help breakdown food, the stomach protects itself and is layered with a mucus membrane that prevents damage from stomach acids.

Once all of this has taken place, the stomach begins emptying its contents into the small intestine.

Stomach emptying occurs very, very slowly. So slow in fact that it can take hours for a meal to completely empty into the intestine. It may be slower or faster, depending on what was eaten.

The first thing to empty is carbohydrates, and then proteins. The slowest moving components are fats and fibers.

This is why fat, fiber, and protein help you feel more satiated and for longer. On the other hand, carbohydrates tend to fill you up, but then leave you feeling hungry not too long after.

The stomach is separated from the small intestine by the pyloric sphincter, which is similar to the LES in function, and doesn’t allow digested food to pass through until its ready, or contents of the small intestine to flow back up into the stomach.

The Small Intestine

Once the digested food moves into the small intestine, it stays there for a while. I'm talking up to 8 hours! This long transit time allows for a large percentage of nutrients to be reabsorbed and used by the body.

The small intestine is composed of 3 parts:

· The Duodenum

· The Jejunum

· The Illium

Most of the absorption of nutrients occurs in the duodenum and the jejunum. The Ilium absorbs vitamins, bile salts, and leftovers that weren’t previously absorbed.

The Large Intestine

Once the remaining food enters the large intestine, it will stay there even longer than the time it stayed in the small intestine (12-25 hours).

The large intestine absorbs things like water, fatty acids, gasses, and vitamins.

After all of these things have been absorbed, we are left with the final product.


Once the feces reaches the end of the large intestine, it moves through the rectum and is excreted by the anus.

When Things Go Wrong

Everything mentioned above assumes everything goes smoothly. You have no allergies, no food intolerances, no GI related conditions and so on. Rarely is it the case that someone has a flawless digestive system that isn’t a little picky about something.

This is where it becomes important to know how to manipulate your food choices and dietary intake to reduce or alleviate digestive problems that might occur regularly.

For example, a large amount of people in the population consume dairy. However, a much smaller number of people actually have the enzyme responsible for breaking down lactose (milk sugar) which is called lactase.

As a result, lactose remains in the intestine longer than it should, any other bacteria break it down instead of the missing enzyme. This results in gas, bloating, and other digestive problems.

Just like food preferences and dietary goals, GI sensitivities are individualized, and one prescribed diet may look healthy at a glance, but it can’t possibly account for specific food intolerances.

Bloat be Gone

So how do you minimize these issues? Especially when it’s hard to identify which foods are

causing them?

Stick to Whole, Minimally Processed Foods

Many GI issues stem from overly processed foods that contain added ingredients and preservatives that our GI tract isn’t very fond of.

Eating mainly Whole Foods means less of a chance of GI issues from processed foods.


Believe it or not, exercise is good for gastrointestinal health and it helps move things along the GI tract.

Keep Your Gut Healthy

Including foods such as Greek yogurt and kimchi can help nourish your microbiome with “good” bacteria.

Your microbiome is a very important player in not only digestion, but many other aspects of your health.

It warrants its own blog post, so we’ll touch on that in the future.

Experiment with an Elimination Diet

If you’re having trouble finding out which food may be the culprit, try an elimination diet to determine which food is the troublemaker.

Hopefully, you now have a better idea of how your digestive system works as well as some strategies to help it continue working well! Again, an individualized approach to eating is required, as well as some experimentation, to find out what works best for you and your unique digestive tract.


Want to find out more about how to craft an approach to eating that will fit in with your needs, goals, and lifestyle? Well, starting today you can work with Med Gym's own Precision Nutrition Certified Coach, Chris Zinn, in our brand new Nutrition Coaching Program!

If you've tried diet after diet and struggled to reach your goals, nutrition coaching may be the answer you need. Working with a qualified nutrition coach to find, craft and stick to the plan that is the right fit for you can be game changing!

Contact us here to learn more about the nutrition coaching program and how you can get started.

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