How Digestion Works
Digestive problems are a real concern for many people. They range from belching to severe acid reflux, mild abdominal pain to ulcerative colitis and Crohn’s, slow digestion with constipation to fast digestion with diarrhea. Like many concepts about our bodies, digestion seems so complex and helping problems seems mysterious due to the limited descriptions of western medicine. The natural language of Chinese medicine on the other hand makes digestion easier to grasp.
With the sheer variety and volume of food and emotions that enter the digestive system, it is no wonder that so many people have digestive problems. Processing our frequent intake is a beautifully choreographed process of warming, chemical infusion, movement, extraction and synchronization. There is immune monitoring of these inputs, the interactions with so many varieties of beneficial microbes in the gut biome, and the enzyme production and release by organs and glands that must be perfectly timed.
Our digestive process is like an active international border checkpoint with movement across a physical barrier monitored by a security force. Most travelers are legitimate visitors, some are a dangerous threat. Security does its best to detect criminals but sometimes one slips in and creates problems. At the border there can also be a clash of cultures with incompatible values, high traffic volume that slows down processing and undocumented travelers that shouldn’t be allowed to pass. The situation can heat up with security using force to confront unruly crowds. Sometimes movement across the border flows smoothly, sometimes there are problems that disrupt or slow it down, sometimes there are lots of travelers and sometimes there are very few. It is a dynamic place.
Let me try to simplify digestion for you. Your digestive tract is the tube that starts at your lips and passes through the center of your body to your anus. It includes your mouth, esophagus, stomach, small intestine, liver, gallbladder, pancreas, large intestine and colon. Its movement is from top to bottom, an obvious but important consideration in Chinese medicine. Wei Chi is the general term for all aspects of the immune system (see my article Focus on Immune System.) In our gut Wei Chi is the security force that not only monitors and controls outside germs, but is also responsible for peristalsis, the wavelike muscle contractions that moves food downward through the digestive tract.
The physical function of digestion is to break down the energy of earth (food) into tiny particles called nutrients and transfer them through the wall of the small intestine into the blood. Nutrients combine with energy of heaven (oxygen) at the lung and are circulated by the heart in the blood to fuel all the cells of the body. The gut wall of the small and large intestines is therefore the interface of the outside world with the inside world. To control what comes in from outside, the cells of the gut wall link together with tight junctions. These regulate what particles can cross the wall to the capillary blood vessels and into the blood. In a healthy state this is limited to nutrients. When the gut is inflamed the tight junctions swell open and allow large food particles to pass to the blood, a condition known as leaky gut syndrome. This overloads the liver causing more inflammation.
Our digestion is also where emotions are processed. Just like food, we have a steady diet of emotions coming at us from the world that require sorting. We have to chew on them, digest them, and assimilate or eliminate them. Most folks have experienced an upset stomach and/or diarrhea from emotional challenges—a clear example of a physical effect of emotional challenges.
Warm Metabolic Process
Human beings are warm-blooded. Everything about our emotional and physical function is warm. The most satisfying emotions are warm ones, the most brutal are cold. Physiological functions work best at 98.5°F. We are stiff when it is cold outside. Digestion only works well when it is warm. (Learn more in my article Ice and NSAIDs Disrupt the Healing of Injuries.)
Chinese medicine describes many contributions of warmth to the digestive process. Fire is the word for warmth. Digestive fire is the metabolic warmth of digestion. Contributions of fire to digestion start with the kidney fire—the pilot light of the digestive process. In the stomach, fire is generated on demand when food enters. It is represented by the production of hydrochloric acid. The small intestine is part of the organ system called the Fire Phase, which also includes the heart and small intestine. It is warm by nature. Liver fire is represented by bile and enzymes which are catalysts that break down fat and protein. Catalysts speed up chemical reactions, like heat making things move faster in all of nature. The pancreas contributes a variety of enzymes, which are more catalysts to combust and break down carbohydrates, protein and fat.
A Tour of your Digestive Tract
Your mouth has many functions, including welcoming food, tasting and chewing, and adding enzymes and fluid to initiate breakdown of food.
The stomach’s job is to ripen and rot. Rotting is a composting process and it is no coincidence that our gut flora (microbial probiotic content, gut biome) are very similar to those in the soil. The stomach’s very hot hydrochloric acid both sterilizes and cooks, lessening the pathogenic threat and accelerating food disintegration, especially protein. The energy of the stomach moves downward so digestion moves from top to bottom. However, when a strong pathological threat is encountered in the stomach, its healthy defense is to rebel—to vomit—sending the contents back up and out.
The small intestine Is responsible for the separation of pure and impure. This is where the vast majority of absorption of nutrients into the blood takes place. It is on average 22 ft long and has a surface area of a tennis court. This huge area (known as the gut wall) is where the outside world meets our inside environment, where food meets blood. Fire contributions called liver and pancreatic enzymes are released into different sections of the small intestine.
The liver manufactures bile and enzymes. Bile is stored by the gallbladder and released into the small intestine in the presence of fat. Bile emulsifies fat into tiny droplets so that enzymes from the pancreas can break it down for final use at blood level. Liver enzymes also enter the small intestine to break down protein.
The pancreas manufactures and secretes many different enzymes—the catalysts to break down fat, protein and carbohydrates into usable nutrients. It also produces insulin whose role is to allow sugar into cells to be burned. Insulin is the hormone of energy storage.
The large intestine assimilates and eliminates. This is where the final digestion of food takes place via fermentation by gut flora. Here, water and nutrients are reabsorbed from the stool into the blood. Finally, like a car’s exhaust pipe, the solid waste from the warm combustion process of digestion is eliminated through the colon with bowel movements.
As with physical food, our emotional encounters go through a digestive process. In the mouth we chew on our perceptions and experiences of the world. In the stomach we develop feelings about these stimuli and compare them to our gut feelings. Denial of feelings disrupts the stomach and can cause an digestive upset.
The small intestine separates pure from impure, fact from fiction, truth from lies, right from wrong. It is our self-feedback mechanism and is damaged by constant comparison to others.
The large intestine assimilates the pure and eliminates the impure. Too much stimulation like bright lights, constant entertainment, and loud noise can impair large intestine function and foster hypersensitivity.
The liver is the general, responsible for the free flow of energy in the entire body and the free and easy movement through life. Anger and frustration disrupt the general.
The gallbladder is the judge, directing our decision making.
Well-functioning digestion is a joy to experience and it is critical to our health. With a diet that is simple to digest there is a feeling of lightness in your abdomen and your life. There is also a greater ability to handle stress since over-taxed digestion demands large amounts of energy which is a stress for the body and being. Eating fewer types of foods at each meal eases the very complex digestive process and quickly helps with bloating, elimination and stress.
If digestion is not functioning well no other system in our body can function optimally. The simplest thing you can do to increase and recover your gut health is to keep your physical and emotional diets warm and simple. As I have written about in How Cold Food and Drink Affect Digestion, we are warm-blooded beings and digestion is a warm metabolic process. No chemical or physiological process in the body works better when it is cold. Cold food and drink lead to inflammation in your gut as your immune system responds to warm up and contain the cold. Inflammation leads to a range of issues including GERD, IBS, gastritis, constipation, leaky gut syndrome, ulcerative colitis, Crohn’s disease, diverticulitis and stomach ulcers. These are all inflammatory bowel diseases.
Inflammation can also be fueled by foods that create heat. These include onions, garlic, sugar, coffee, chocolate, alcohol, dairy products, and nightshade-family vegetables. The stimulatory heat of hot foods is called toxic heat and damages fluids and tissues. To minimize damage from the fire the body once again creates an inflammatory response and mobilizes cooling substances to counteract the heat.
Seat of the Immune System
We think of digestion as an internal process but it is in fact external. The transition from the skin on your face over your lips and into your mouth is simply changing the type of skin, from that exposed to the air to the slippery mucosal skin exposed to food and fluid. Both surfaces are exposed to the outside world.
There is enough bacteria on each bite of food to kill us. This is why our immune system is constantly active in our digestive tract. As food moves through the digestive tube, the immune system monitors it and uses the mechanism of oral tolerance, selectively allowing most germs to pass through without attacking them. When a toxin or more threatening pathogen is present the immune system responds with heat and swelling—meaning inflammation—in an attempt to neutralize it. Vomiting pathogens back to the outside is a fantastic, healthy mechanism to prevent illness at a deeper level.
Our gut is colonized by a load of beneficial bacteria, fungi and viruses known as the gut microbiome or gut flora. It makes up 5 to 8 pounds of our weight. It has such a diverse population that there is 100 times more genetic content in this biome than in the human genome (meaning that we are more other than us!). It is embedded in the stomach yin also known as mucosal lining of the digestive tract.
This ecosystem in our gut wall is therefore our interface with the outside world. It is impossible to say where the outside stops and we start. We relate and adapt to the external environment via viruses, bacteria and fungi, they are not just pathogens that attack us. Our probiotic friends not only digest, they also produce many chemicals for our body. For example serotonin, responsible for so many important functions in our brains, is mostly produced by gut flora, not secreted by a gland. This is a great example of us being part of nature, inextricable from it.
Finally, cooking for yourself is an act of self-care and self-love like no other. The feeling that comes with preparing your own food is at once calming, satisfying and empowering. The messages contained in the act are that you can create, you can nourish yourself, you can accomplish something, you have the knowledge and skill to take care of yourself, and you can survive. These are powerful feelings that promote emotional and physical health.
Welcoming Food by Andrew Sterman. This is a beautifully written, simple to understand volume. It is informed by the dietary concepts taught in Chinese medicine. https://www.amazon.com/Welcoming-Food-Book-Energetics-Medicine/dp/0983772096