The Microbiome Connection Part 2: by Mark A. Pimentel
Digestion requires constant, synchronized contractions of the various gut muscles to control the movement of food through the gastrointestinal tract. These contractions are known as gut motility. Motility problems can develop when the nerves and/or muscles of the gut are not working properly. Abnormal gut motility can lead to bloating, pain, nausea, and diarrhea or constipation, all of the symptoms related to IBS. When gut motility is working well, during the feeding phase the stomach pushes food mixed with acid toward the pylorus, which senses whether the food is broken down enough to allow it to pass into the small intestine. The small intestine is responsible for mixing and spreading the food to maximize protein and sugar break down, as well as mixing fats and bile into little packages during the feeding phase. When the stomach is full of food and distends, the gastrocolic reflex signals the colon to empty, and the colon pushes stool forward. This is why you occasionally have a bowel movement after eating. The reflex also functions to drive the existing intestinal contents through the gastrointestinal tract to help make way for ingested food. The very act of eating can provoke an overreaction of this reflex in some patients with IBS because of their heightened visceral (intestinal) sensitivity. IBS patients tend to describe the experience of pain within the internal organs (the viscera) at a more intense level than normal, leading to the classic symptoms of IBS. The Fasting Phase After the feeding phase ends, the fasting phase begins. Initially the small bowel doesn’t move or only partially moves such that food gets mixed with enzymes in the small intestine. When digestion is complete, housekeeper cleaning waves (also known as migrating motor complexes phase 3) begin and occur every 90 to 120 minutes for a few minutes at a time. The waves move into the small intestine, where they push the remnants of undigested food, bowel secretions, and excess bacteria forward and dump them into the large intestine. The housekeeper function is one of the keys to understanding IBS. For those who are significantly affected by IBS, the housekeeping role malfunctions and “cleaning” of the bowel is impaired; that is, more bacteria accumulate and grow on the debris in the small intestine, producing many side-products—including gas—which leads to bloating, abdominal distension, diarrhea, or constipation. Motility issues can also stem from problems in gut immunity. Your gut has millions of immune cells—more immune cells than anywhere else in your body. The intestinal immune system encounters more antigens—toxins or other foreign substances that induce an immune response—than any other part of the body. That’s because you’re bringing the outside world into your body by eating. You need defenses. Your gut is also the home of the body’s largest microbiome. This microbiome ideally contains a healthy balance of bacteria, as well as fungi, parasites, viruses, and archaea (single-cell organisms, including methanogens, which produce methane gas as a metabolic by-product). These microbes live throughout your digestive system. They live in your mouth and in your intestines, and they have different functions and interactions. If the delicate balance of the microbiome is upset, for example, by food poisoning or excessive bacteria in the small intestine, you may develop IBS. Everything you eat affects your microbiome. Various dietary patterns shape the microbiome and can lead to differences in immunity. A more diverse gut microbiome can lead to a more robust, adaptable immune system. The wide variety of protective bacterial strains already found in your gut were partly passed down from your mother at childbirth. Antibiotics, diet, infections, and other factors may reduce their abundance, but these bacteria are usually not completely eradicated. It’s important to nurture and reinforce a healthy gut microbiome. There are numerous beneficial functions of a healthy gut microbiome. Gut microbes modulate other bacteria and facilitate the extraction and fermentation of dietary fibers. They generate heat and can change your basal metabolic rate. They also produce vitamins and are mediators of peptides (small proteins), which play key roles in regulating the activities of other molecules, modulating immune responses, and influencing other bacteria. The way in which the microbiome interacts with the body is important to gastrointestinal function. The human microbiome produces some of the same compounds that are produced by human cells. For example, the microbiome secretes serotonin, a mood chemical, leading some researchers to believe that bacteria can influence mood as well as insulin-like proteins and other chemicals that allow your body to function. Serotonin has a neuromodulating effect that causes nerves to fire and modulate gut function. A disruption in the microbiome may increase serotonin levels and can lead to diarrhea, or, if hormone production is reduced, constipation. Your microbiome contains five specific components that promote health and ward off disease. Diversity of bacteria and fungi in the gut. In the large microbiome city of your gut, the more diverse the population, the healthier it is. You wouldn’t want a city filled only with doctors or lawyers, for example. Distribution of bacteria and fungi. Differing types of bacteria are positioned strategically throughout the gut. For example, the colon bacteria are different from the small intestine bacteria because accumulation of bacteria from the colon in the small intestine leads to SIBO and its associated symptoms. Number and composition of bacteria. In the scientific literature this is described as relative or absolute abundance. With thousands of varieties of bacteria, your microbiome city has occupants with characteristics that allow them to complete their specific tasks. The number of each microbe is proportional to its roles and functions. Five plumbers would not be enough for a big city. You need the right amount of each bacterium for functioning harmony. Products of bacteria. The many inhabitants of your microbiome city produce a wide variety of products, some of which are good and others are bad. For example, some bacteria have properties that reduce inflammation in the gut and others promote normal motility. On the other hand, gas and other chemicals produced by bacteria in the microbiome can contribute to the symptoms of IBS. It’s important to understand that bacteria are not “good” or “bad” all the time. It’s more about maintaining balance in your microbiome. Resiliency. If you look at your microbiome after taking antibiotics, you’ll likely find that the numbers of microorganisms are drastically reduced. Two weeks later, the bacteria repopulate your gut and the microbiome snaps back to normal. That’s resiliency. But if you continue to take courses antibiotics, they can adversely affect your microbiome. The microbiome is like an elastic band that becomes a little less stretchy every time you pull on it. It may not snap back all the way if you take too many antibiotics. Food additives can also disrupt the microbiome. For example, emulsifiers are added to food to make it creamy, or sodium benzoate is added to reduce fungal growth and preserve shelf life. These additives make food more appealing, but they have the potential to disrupt the microbiome. An emulsifier such as polysorbate 80 disrupts mucous membranes and, in effect, emulsifies your microbiome too. And sodium benzoate kills fungi that are supposed to be in the microbiome.
