An Overview of Digestion
Before we talk more about specific nutrients, I would like to address how our bodies break food down into the nutritional molecules we need and how we then move them around our bodies. It may seem counterintuitive, but our digestive tract is technically outside of our body.
We can think of the surface of our digestive tract as a continuation of our skin, creating a barrier between the food that we put in our mouths and our vital organs. This is for good reason. Everything we eat is potentially harmful to us. Our digestive system does the work of sorting out what our cells can use to maintain the work of life and what needs to be eliminated including indigestible substances, potential toxins, and potentially harmful microbes.
If you eat something and feel unwell afterwards, it’s a sign that your digestive system is working hard to protect you from it. Immediate symptoms usually result from an effort to purge something irritating from your digestive system. Another possibility is a reaction to the activity of the microbes that live in your digestive tract. Take lactose intolerance for an example: those who are lactose intolerant lack the enzyme that breaks lactose down into its absorbable components. When undigested lactose enters the large intestine, bacteria there are happy to digest and eat it. Unfortunately, when they do, they create irritating byproducts and gas which initiate the symptoms of lactose intolerance: diarrhea, gas, bloating, abdominal cramping, and nausea. This can be prevented by avoiding lactose or using dairy products that have had the lactose chemically pre-digested.
Because our digestive system is one of the areas where things from the outside can enter our body, it is full of immune tissue. This is another reason why dietary changes can have a major impact on chronic inflammatory conditions such as allergies, arthritis, heart disease, and autoimmune conditions. It is also why we often see problems with digestion commonly occurring with these chronic conditions. One of the best things you can do for your overall health is to get your digestion on track. This is why many integrative practitioners focus so much on digestion and diet - it’s where our health starts.
Let’s explore the complex and beautiful thing we call digestion shall we?
Healthy Digestion - What it feels and looks like
If you find yourself thinking about your digestion, what foods upset your stomach, whether or not you will have heartburn, or being constantly aware of where the bathroom is, chances are your digestive system isn’t functioning optimally.
A healthy digestive system does its job without much thought from you. You wake up, perhaps have a morning bowel movement, find yourself hungry shortly after rising and feed yourself food that makes you feel satisfied and fueled. A few hours later, you find yourself hungry again, and you eat lunch. Later that afternoon or early evening, you are hungry for dinner, and you eat again. There may be 2-3 small snacks between meals or not depending on your activity level and the size of your meals. After each major meal, it’s common to have another bowel movement.
Bowel movements are smooth and easy with no real effort required. They themselves are absent of undigested food, blood, or mucus and are well formed and of a soft serve ice cream consistency. There is no pain, minimal gas, no nausea, and a robust appetite that is easily met.
If you do not experience digestion this way, it’s time to talk with your health care team about your digestive health. As we explore digestion, we will look at a few common areas where digestive issues arise. This may aid you in your conversations and search for healing.
The First Phase of Digestion - It’s all in your head
Digestion begins before you take your first bite of food. It starts when you see, smell, or think about food. This is called the cephalic phase of digestion (cephalic = head). This phase of digestion lasts only a few minutes but it’s akin to warming up your car engine before driving away on a cold day. Signals from the hypothalamus in your brain travel down your vagus nerve and trigger the release of digestive juices like saliva, stomach acid, and enzymes. When we lack an appetite or are depressed, this phase of digestion doesn’t occur.
Then, if we are able, we begin to eat.
Physical and chemical digestion begin in the mouth where our teeth and tongue grind each bite into a form that can be swallowed while saliva is mixed in. Saliva is full of enzymes that begin to break down carbohydrates. It also moistens our food, making it easier to swallow, and dissolves chemicals within food allowing them to interact with our taste buds so we can taste them. Saliva also contains protective chemicals to weaken and kill bacteria.
If you frequently experience dry mouth and lack of saliva production, first ensure you are not dehydrated, and then consult with your dentist and doctor for evaluation, diagnosis, and treatment. Chronically dry mouth can be due to autoimmune disease or other causes and often results in tooth decay, gum disease, and eventually periodontal disease. Chronic infections and inflammation in the mouth can also have long-term and body-wide health implications.
Once our food has been chewed, our tongue moves it to the back of our mouth as a mass called a bolus and it’s ready to be swallowed.
When we swallow, the bolus is quickly moved down our muscular esophagus in wave-like contractions, known as peristalsis, to our stomach. Food doesn’t fall into our stomach; it is purposefully moved there. This is why astronauts can eat in space and why you can eat while laying horizontal or upside down. Difficulty with swallowing is known as dysphagia and can be due to several different causes, some of which can be life-changing or -threatening. If you are experiencing difficulty or pain with swallowing, be sure to schedule a visit with your doctor for evaluation, diagnosis, and treatment.
Another common digestive complaint occurs here at the intersection of the esophagus and the stomach: GERD/heartburn/reflux. Often, people are prescribed antacids to address GERD. This may ease the burning sensation temporarily; however, it isn’t a cure and has long-term significant health consequences including osteoporosis, kidney disease, dementia, and mineral deficiencies. Chronic uncontrolled GERD isn’t any safer and can lead to esophageal cancer, the treatment of which can be disfiguring and have serious negative effects on a person’s quality of life.
GERD can be caused by several factors including poor diet, some medications, alcohol consumption, low stomach acid due to chronic stress or zinc deficiency, hiatal hernia, or pregnancy. Make sure to discuss your symptoms with your doctor, and if all they offer is acid suppressive therapy, consider contacting a Naturopathic Physician or other integrative practitioner for more options.
The Second Phase of Digestion - It happens in your stomach
The next step in digestion occurs in your stomach. Once food enters your stomach it will be further broken down and mixed with more chemicals. This phase lasts for about three hours. Between bites, the door between your stomach and esophagus (the lower esophageal sphincter) closes, preventing food and digestive juices from splashing back up as your stomach churns and mixes its contents like a washing machine.
As food enters and stretches the stomach, nerves there trigger the release of hormones, enzymes, and hydrochloric acid. This lowers the pH of the stomach to around 2, which is quite acidic, and begins the digestion of proteins and kills more bacteria. This acidity also frees minerals that are bound up in proteins, making them available for absorption in the small intestine.
Hormonal control features help keep the stomach from getting too acidic, protecting us from developing ulcers. Stress can inhibit this function as well as lower stomach acid production, causing an environment that is too acidic or not acidic enough. The first symptom of either situation is often heartburn. Ulcers--when addressed correctly--can heal quickly, but if left untended, can cause chronic blood loss resulting in anemia and in some cases can become big enough to risk perforation of the stomach, which is a life threatening issue. The bacteria H. pylori has also been associated with disruption of the acid control system and an increased risk of developing ulcers and should be screened for in people with ulcers or unresponsive heartburn.
Another potential area of concern is delayed gastric emptying which can occur due to damage to the nerves in the stomach from injury, infection, nervous system disorders, or uncontrolled diabetes. If you often find yourself full after a few bites of food and uncomfortable in the area under your left lower ribs after eating, you may be encountering delayed gastric emptying and should consult with your doctor.
The Third Phase of Digestion - The small intestine
Thus far, digestion has focused on the physical and chemical breakdown of food and the elimination of potentially harmful bacteria and other microorganisms. Here we continue the chemical breakdown of food and begin the process of absorption. This next phase of digestion lasts 3-6 hours.
Partially digested food is now in a liquid state known as chyme. It will now exit the stomach through another sphincter and enter the first portion of the small intestine: the duodenum. When chyme enters the duodenum, signals are sent up to the brain to stop stomach acid secretion and begin the next phase of digestion. If too much chyme enters the small intestine too quickly, hard brakes are triggered causing nausea and vomiting. This is common in people who have had their stomach volume reduced and is known as dumping syndrome.
Once the chyme enters the duodenum, the liver and pancreas play their role in the breakdown of your meal. The gallbladder holds fat digesting bile that was produced by the liver. In response to fat entering the duodenum, bile is released into the duodenum, breaking fats down into triglycerides for absorption. The pancreas releases bicarbonate to neutralize the acidity of the chyme and additional enzymes to further the breakdown of proteins and carbohydrates. Enzymes produced by the cells that form the “skin” of the small intestine finish the digestion of carbohydrates and proteins and it is through these cells that nutrients, medications, and other substances are absorbed into the bloodstream where they will first pass through the liver to be acted on before circulating through the rest of the body.
Digestive issues can arise in the duodenum as well. Gallstones are a common issue that can cause significant pain and often lead to surgery. Once a gallbladder has been removed, the controlled release of bile has ended. For some, this can lead to long-term trouble digesting fatty foods and/or chronic diarrhea. Risk factors for developing gallstones include: a high fat/low fiber diet like the Standard American Diet (it is quite SAD), obesity, pregnancy, lack of exercise, family history of gallstones, diabetes, rapid weight loss, medications that contain estrogen like birth control pills or hormone replacement therapy, and liver disease.
Additional issues can arise with chronic stress or a habit of eating on the run. This creates chaos in the dance between our nervous system and our digestive system leading to poorly timed or limited release of bile and pancreatic enzymes causing incomplete digestion.
Incompletely digested foods are eliminated without us benefiting from their nutrients and create chaos on their way out, often in the form of diarrhea, gas and bloating, or constipation. Alternatively, these incompletely digested substances can be absorbed if the lining of our intestines is inflamed and leaky. This is a condition known as increased intestinal permeability or “leaky gut syndrome”. These partially broken down substances can create problems as they aren’t recognized as nutrients but rather as potential foreign invaders, stimulating an immune response. These are the foods we often see pop up on blood tests for food sensitivities. The results do not necessarily mean that these are foods that your body cannot digest, but they are often an indication of this increased intestinal permeability. This is not an allergy, but it is a hypersensitivity reaction caused by poor digestion. If you avoid these foods and work on improving your digestive health, you may be able to resume eating them once your gut lining has healed.
A few steps you can take to support digestion are: eating in a relaxed environment, thorough chewing, and eating bitter foods and herbs to help stimulate the release of digestive juices. In long-term cases, the short-term supplementation of digestive enzymes can be helpful, but should not be continued long-term to avoid dependency. Herbs and spices have been added to foods for millenia to prevent spoiling, improve flavor, and to support digestion. We will go into this topic in more detail in the months to come.
The Final Steps: The large intestine
After the remains of your meal have finished their trip through the small intestine, they enter the large intestine for the final 12-24 hours of their trip. Here water is absorbed, our resident friendly bacteria synthesize B vitamins and vitamin K from nutritional precursors and digest fibers from our food, creating short chain fatty acids and other substances that feed our large intestine cells, reduce inflammation, and trigger feelings of satiety.
Problems here include diarrhea and constipation. Frequent diarrhea or constipation are often classified as irritable bowel syndrome and can usually be addressed through diet and stress management. Diarrhea or constipation coupled with blood and/or mucus should be evaluated by a doctor. There are several autoimmune conditions that can trigger these symptoms, and cancer is another diagnosis that should be evaluated. Chronic blood loss leads to anemia which creates fatigue and additional long-term consequences.
Hemorrhoids are another common issue here and result from pressure on the blood vessels of the rectum due to pregnancy, straining with bowel movements, and chronic constipation along with lax tissues from nutrient deficiencies.
Applications
As you can see, our digestive system is much more complex than many people imagine. Simply eating food or taking supplements doesn’t ensure those nutrients will enter your body and benefit you. Our digestive system is a complex relationship between our organs, hormonal systems, and our nervous and immune systems. It functions to keep us nourished while protecting us from infection and poisoning, and also contains off switches that allow us to jump up and run from danger at a moment’s notice.
These built in braking mechanisms allowed our ancestors to rapidly switch from a state of relaxed digestion to one capable of running or fighting. This allowed our species to survive predators and catastrophe, but also creates trouble when we live under chronic stress and pressure - we must relax to fully digest. Many people live with chronically high levels of stress, resulting in numerous long-term health complications. We can even see evidence of these complications passing from one generation to the next.
By better understanding how our digestive systems work, we can work with them and increase our health at the same time. We can also prioritize community health through better access to healthy whole foods, uplifting the health of us all.
If you are living with chronic digestive complaints, I encourage you to reach out to your doctor for help and support. A correct diagnosis and treatment can help you heal, avoid additional illness, and give you the energy and nutrition you need to live your life. Don’t make the mistake of ignoring or living with digestive problems; the consequences can be much bigger, more painful, and more expensive than the treatment you need.
Next Week
Next week, we will discuss supplements, the role they play, how to evaluate the safety and quality of a supplement, how to talk to your doctor about supplements, and why food is always better than taking a supplement. A quick preview - do not purchase store brand supplements especially from Walmart, and do not buy supplements online through Amazon - they are cheaper for an insidious reason!
To our health!
References and Resources for Further Exploration
Marieb, E, Hoehn, K, Human Anatomy and Physiology, Ninth Edition - Instructor’s Review Copy, Pearson, 2013
Dr. Currey’s presentation on the digestive system for Elementary students:
Article on how increased intestinal permeability is linked with Crohn’s Disease
