The Role of the Migrating Motor Complex in IBS and SIBO
The migrating motor complex (MMC) is one of our body’s most important mechanisms for proper digestion. This mechanism refers to the periodic mobility pattern that occurs in the upper gastrointestinal (GI) tract, including the stomach and small intestine, during the fasting state. We call the MMC the “housekeeper” of the small intestine because these contraction patterns clear out any food particles from the small intestine and send them to the large intestine between meals.
The MMC occurs in 4 phases. In phase 1, there are no contractions present. Phase 2 has contractions present, but the interval between contractions is irregular. Phase 3 is the most active and powerful phase, where 2-3 contractions per minute are present in the stomach and 11-12 contractions per minute are present in the small intestine. Phase 4 mimics phase 2. After phase 4, phase 1 begins again, unless disrupted by food intake from the next meal or snack. The length of the MMC cycle appears to vary between individuals and can vary on a daily basis. The duration of the cycle also seems to be dependant on the origin of phase 3 (stomach or small intestine) and on the intragastric pH level. The more acidic the pH, the longer duration of the MMC. Some believe the cycle length ranges from 113-230 minutes, others believe it may be closer to 90-120 minutes.
The major hormonal regulator of the MMC is motilin, a gastroprokinetic hormone. Motilin is produced by endocrine cells of the proximal small intestine, and levels are shown to peak just before phase 3 of the MMC begins. This only happens with gastric-onset phase 3 contractions. Research suggests that the motilin-induced phase 3 contractions may signal hunger. The MMC is also thought to be regulated by the vagus nerve and phase 3 contractions may also be regulated by ghrelin, which is known as the hunger hormone.
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Role in IBS and SIBO
An absent or disordered pattern of the MMC is associated with small intestinal bacterial overgrowth (SIBO). This is mostly likely due to the increase of food particles in the small intestine, which can increase bacteria in the small intestine, leading to overgrowth. A poorly functioning MMC may also be linked to chronic constipation, which can be seen with irritable bowel syndrome (IBS). Supporting the function of the MMC may decrease risk of SIBO and improve symptoms of constipation, gas, and bloating with IBS.
The best way to support the function of the MMC is to space out fasting to allow the full MMC cycle to occur between meals and snacks. The ideal time between is 3-4 hours. This is not meant to be a rigid guideline to stick to, but is one to work towards. To increase space between meals and snacks, ensure they are well-balanced and contain fiber and healthy fats for increased satiety over longer periods of time.
If the MMC function is disordered, a prokinetic agent can be helpful. This is typically used for those with SIBO and chronic constipation. If you think you may be at risk for a poorly functioning MMC, you can discuss the use of these with your doctor and dietitian. Know that supporting the MMC may be a key part of IBS and SIBO management, but it may not be the only piece of the puzzle. If you do not already have a diagnosis for the symptoms you are experiencing, see a gastroenterologist. If you do have a diagnosis and you need a plan for managing symptoms and improving your gut health, apply for a consult to determine if my services would be a good fit!
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