The 5 Stages of Digestion

Digestion is undoubtedly one of the most important foundations of health. Every cell of every tissue in your body depends on good digestion to break down and assimilate vital nutrients. While digestion may seem like an automatic process that you have no control over, that really isn’t the case. Understanding how the system works, and what components are necessary for optimal gastrointestinal (GI) function is the first step towards taking control of your digestive health. The first thing to know is that digestion is a north to south process, starting in the brain, working its way south to the colon. Though it is a long and complex system with many moving parts, here I’ve broken it down into five stages. When there is a hiccup or deficiency anywhere along the north to south chain, everything south is effected, and often times digestive issues seen at the end (in the colon) can be traced much further north.

The Five Stages of Digestion:

1. The Brain + The Parasympathetic State

Our society is chronically stressed out; This is no secret. We work long hours, don’t spend enough time in nature, and have exposure to many chemicals and toxins that didn’t exist 100 years ago. We spend too much time on screens and inside and too little time relaxing with friends, playing, moving, and resting. I don’t remember how many hours the average “work week” of a hunter/gatherer was but I know it wasn’t anywhere near the 40 we consider the minimum work week today. People used to prioritize time to just be. Being overly busy takes its toll on many aspects of our mental + physical wellbeing, but one of the most notable effects it has is on our digestion.

Fight or Flight vs. Rest + Digest

Your (autonomic) nervous system is primarily comprised of two parts – the sympathetic, which entails your fight, flight or freeze response – and the parasympathetic, which involves the rest + digest activities. You are always in either a sympathetic or parasympathetic state depending on which activities are taking place, and both cannot happen at the same time. If you’re overworked, stuck in traffic, running around the city at rush hour, late to your next appointment or getting yelled at by your boss, you’re in a sympathetic state, meaning blood flow is directed to the extremities, pupils are dilated, blood sugar is elevated, etc. When you’re eating a meal, however, you should be in a parasympathetic state. This is where the whole body relaxes, blood flow goes to the digestive and reproductive organs, and organs like the adrenal glands produce reproductive hormones in favor of stress hormones like adrenaline.

Essentially, you need to be in a relaxed, parasympathetic, rest and digest state in order to properly digest your food. When people get stressed out and loose their appetite, this is their body’s way of saying “we aren’t in a place to digest food right now.” The digestive juices needed to break down food aren’t produced, which leads to a whole cascade of effects and symptoms. This is why it’s crucial to relax at meal time; Put down the screen, take some deep breaths into your low belly, give gratitude for the food, smile, be present, be stationary (not driving or multi tasking)… you get the idea! Then your nervous system will know it’s time to digest, not escape danger which is what the perception of stress communicates.

2. The Mouth – Saliva, Enzymes + Chewing

The next stage of digestion occurs in the mouth. Once you’re relaxed and food is in front of you, the next thing that should happen is that your body sees and smells food. Your sensory organs signal to the brain that food is present. This then signals to the stomach to start producing stomach acid and the pancreas to start producing enzymes. Additional enzyme production occurs right in the mouth. Saliva is also generated and secreted through salivary glands. Before you even swallow, you’re already beginning to digest your meal, which sets the stage for good digestion lower down.

The combination of saliva, enzymes and the mechanics of chewing is the second opportunity you have to establish good digestion (after getting in the parasympathetic state of mind).

3. The Stomach Juices + Minerals

Once you start eating, food travels down to the stomach where it is bathed it highly acidic gastric juices including hydrochloric acid (HCL) and pepsin for the breakdown of proteins. The pH of stomach acid is around 1.5-3, low enough to incinerate metal. A barrier of mucous protects the stomach lining itself from being dissolved by the acid. If chewing (part of stage 2) was the mechanical breakdown of the food, the bath of stomach acid is the chemical breakdown. This is where any bacteria and pathogens are killed and the food itself is turned into an acidic paste called chyme. When the pH becomes low enough, the chyme signals to the pyloric sphincter (the doorway to the small intestine) to open and allow the food paste to travel onwards on its journey.

It should be noted that HCL is made up of nutrients like zinc, b5, etc. Without these minerals, there may be an insufficiency of HCL, causing problems further down the digestive tract.

4. The Duodenum- Bicarbonate, Enzymes, + Bile

Once in the upper part of the small intestine, known as the duodenum, the chyme no longer needs to be so acidic, so the pancreas releases sodium bicarbonate to neutralize it. It also releases pancreatic enzymes to further work on the breakdown of carbohydrates into glucose molecules and proteins into amino acids + polypeptides. Unlike carbohydrates and proteins, fats require bile to break them down. The liver produces the bile, and stores it in the gallbladder for efficiency. Once fat enters the duodenum, a hormone called CCK tells the gallbladder to release bile through a series of ducts which then helps with the breakdown of the fat globules into more simplified fatty acids and glycerol. Once broken down, most fatty acids travel onward through the lymph system to their destiny as cell membrane building blocks, immune cells, etc. By the time the chyme leaves the duodenum, it is almost completely digested.

5. The Small + Large Intestines

The remaining chyme continues traveling southbound through the small and large intestines where nutrients are slowly absorbed through vast amounts of time and surface area. Millions of vili and microvilli line the inside of the small intestine. It is their job to absorb nutrient molecules into the bloodstream for delivery to different areas of the body. What’s remaining travels through the ileocecal valve into the large intestine. The large intestine, or colon, is where lots of healthy bacteria reside to help with vitamin production including K, B1, B2, B12 and butyric acid. Water, bile and other resources are also reabsorbed in the colon and recycled elsewhere in the body. The large community of bacteria occupying the habitat of your gut is what’s referred to as the gut microbiome. Many believe the gut microbiome is the epicenter of health.

Digestion may sound complicated, and it is. But if you can make sense of the basics of what’s happening in your body, it becomes much easier to recognize where things may be thriving (or not) along the chain. From being in a peaceful state of mind, to chewing thoroughly, there are several easy ways you can improve your own digestion just by understanding how things work and taking a mindful approach to eating. When we influence the chain of digestion higher up through what we can control, that makes an impact lower down which can result in improved overall health. So even though digestion is an autonomic nervous system process, our decisions and awareness can make a huge difference on whether we digest well and thrive or not! Food quality? Now that’s a whole other topic…