I want to discuss a particular phenomenon that I think is pretty amazing. It is the smooth muscle contractions that our stomachs make to push undigested food boluses through our intestines during periods of fasting. Now, that may not strike you as pretty amazing, but it serves as one of the body’s most important mechanisms to ensure proper digestion. This symphonic conglomeration of electromechanical movement is known as the migrating motor complex (the MMC).
One could think of the MMC as the housekeeper for the gastrointestinal system, but this housekeeper only works when no one else is home. Meaning, it is only operational when the digestive system is in a fasting state, as it is modulated by our “rest and digest” enteric nervous system. During this time of fasting, the MMC goes through four phases of contractions which allow food to pass from the stomach to the small intestines and then ultimately to the large intestines. The four phases take anywhere from 90-120 minutes on average, as long as process is not interrupted by food. When a meal is introduced, these muscle contractions, known as peristalsis are put on hold.
The MMC is regulated by several mechanisms, one of which is a prokinetic hormone known as motilin. This is secreted in high levels just before entering phase 3 of the of the process. It is during this time that the signal of hunger in the form of “stomach growling” is thought to emerge. The MMC is also regulated by the vagus nerve which is also responsible for regulation of digestion, breathing, and heart rate. And finally, regulation is thought to occur through a hormone known as ghrelin – our “hunger hormone.”
There are many things that can cause the migrating motor complex to become dysregulated, and the most common one is stress. Stress interrupts the signaling to the MMC which ultimately shuts down the digestion process. Intuitively, this makes sense, because incoming stress signals alert the body that there is a danger nearby, which upregulates the sympathetic “fight or flight” system. This action reallocates bodily resources from the suddenly less important process of digesting food, to the suddenly more important role of preserving self from danger. One can easily see how in a chronic state of stress, digestion would be altered in a continuous way. In addition to stress, and frequent snacking, there are several mechanisms that can cause dysfunction the MMC. These include hypothyroidism, high cholesterol, diabetes, abdominal adhesions, eating disorders, Ehlers Danlos syndrome, certain types of bacterial induced food poisoning, and SIBO.
SIBO is a condition which causes symptoms of bloating, gas, diarrhea, constipation, heartburn, indigestion, or abdominal pain. It is frequently seen in IBS, and occurs when bacteria which should reside in the large intestine, find their way into the small intestine. These displaced bacteria then feed on the carbohydrates that pass through, causing them to ferment, release gas in the form of hydrogen or methane, which leads to digestive symptoms. A dysfunctional MMC often contributes to the proliferation of SIBO by allowing the bacteria a more hospitable environment to set up colonies in the absence of the “housekeeping wave” that would otherwise sweep the bacteria through the digestive tract.
To support the MMC, one of the most useful strategies is to allow around 3-4 hours of space in between each meal or snack, and to ensure plenty of fiber, and healthy fats, to encourage satiety. While most beverages will in fact interrupt the MMC mechanism, water, herbal tea, and black coffee will not. One can also utilize a prokinetic agent, taken in the evening time to encourage that the MMC push the wave of food bolus through the digestive tract and keep you feeling well. Prokinetic supplements are best taken at bedtime, when the body is in a natural state of fasting. Another alternative is having ginger tea.
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See the links below for my favorite Prokinetic:
Miyano Y, Sakata I, Kuroda K, Aizawa S, Tanaka T, Jogahara T, Kurotani R, Sakai T. The role of the vagus nerve in the migrating motor complex and ghrelin- and motilin-induced gastric contraction in suncus. PLoS One. 2013 May 28;8(5):e64777. doi: 10.1371/journal.pone.0064777. PMID: 23724093; PMCID: PMC3665597.
Deloose E, Janssen P, Depoortere I, Tack J. The migrating motor complex: control mechanisms and its role in health and disease. Nat Rev Gastroenterol Hepatol. 2012 Mar 27;9(5):271-85. doi: 10.1038/nrgastro.2012.57. PMID: 22450306.
Xu, Q W et al. “Altered migrating myoelectrical complex in an animal model of cholesterol gallstone disease: the effect of erythromycin.” Gut vol. 43,6 (1998): 817-22. doi:10.1136/gut.43.6.817