A coordinated cleanup that happens in the gut in between meals might have big implications for anyone who struggles with digestive issues.
After eating, a mechanism called the migrating motor complex sends special contractions to rid the upper gastrointestinal (GI) tract of debris, such as bacteria and mucus.
These aren’t the same contractions as those used in gastrointestinal peristalsis, which involves waves of muscle action to move and mix food throughout all the digestive organs. The migrating motor complex (MMC) has been described as a sweeping process, much like a street cleaner following behind a parade.
This MMC is a vital—and somewhat time-consuming—part of optimal digestion that can take place only when one is not eating. Its job is keeping microbes and their byproducts in the right place by sweeping away remnant food particles that gut bacteria like to feed on.
Without this mechanism working properly, bacteria can wander out of the colon where they belong and into the small intestine in search of undigested food. They’re not disease-causing bacteria; they’re only doing their job, just in the wrong location. This condition is known as small intestinal bacterial overgrowth (SIBO), and it leads to gas and bloating, among other symptoms.
“It has been found that individuals who suffer disruption or damage to this system are far more likely to develop [SIBO],” the book reads. “The large intestine has different bacteria strains, and a much higher volume of bacteria than the small intestine. The progressive flushing mechanism of the MMC helps to prevent bacteria strains from the colon moving up into the terminal ileum, where they could begin to colonise the small intestine.”
There’s even concern that dietary advice to eat smaller meals but more often could be contributing to inefficient functioning of the MMC; overburdening the gut with too many feeding episodes could be a contributing factor to uncomfortable GI symptoms.
A Detailed Look at the MMCGut motility, the transit time for our food from the moment it hits our mouth until it works its way all the way through and out of the body, is the major role of the MMC. The MMC and the nervous and endocrine systems have a complex interplay, only some of which is understood.
The most active is the third phase, which has short bursts of regular high-amplitude contractions. They can result in gurgling or rumbling noises often misinterpreted as hunger. Eating will get rid of the noise, but it will interrupt the cycle from the first bite, starting the lengthy process all over again. The fourth phase is a short transition back to the first.
When the MMC Isn’t WorkingResearchers also learn clues about the MMC by studying its intimate link with gut hormones, such as motilin, and the nervous system.
The enteric nervous system—sometimes called the second brain—initiates MMC activity. Part of the autonomic nervous system, the enteric nervous system is a web of neurons that communicates using neurotransmitters—chemical messengers. They coordinate activity with muscles, secretory glands, and the vasculature of the GI tract, according to “Clinical and Basic Neurogastroenterology and Motility.”
An absence of MMC phase three contractions for eight hours is considered severe enteric neuromuscular dysfunction. But there’s another component of the nervous system that’s also at play—the vagus nerve, a long nerve that connects the brain to the body’s major organs, including the gut.
Patients who've had vagotomy, removal of part of their vagus nerve, still have MMC impulses in the small intestine, but not the stomach. This shows that two independent parts of the nervous system are at play in this one mechanism.
MMC and IllnessThe MMC is important not only for aiding in digestion, but also for pushing food through the GI tract, allowing for nutrient absorption and preventing intestinal blockages.
Two of them are intestinal pseudo-obstruction, a painful condition characterized by a buildup of partially digested food in the colon, and gastroparesis, the inability of the stomach to empty properly.
A 2012 study in the Journal of Neurogastroenterology and Motility found that patients with Helicobacter pylori (H. pylori) infections were more likely to have a lack of phase three activity, which returned once H. pylori was eradicated.
Fasting and the MMCOne simple way to restore the MMC function is to allow it to do its job, meaning spreading out eating.
“Our bodies like cycles. When you’re not feeding yourself on a regular cycle, gut function can slow down and stop working,” she said. “Is spacing our meals enough to make a difference? I don’t think we really know at this point.”
Still, it’s common advice—so long as patients aren’t experiencing nutritional deficiencies, which can be common in some with GI issues. Getting sufficient nutrients always takes precedence over meal timing, Ms. Madsen said.
Other Possible Rebalancing ToolsPharmacological prokinetics—agents that promote gut motility—are being explored. You can also find natural prokinetics including probiotics, traditional Chinese and Japanese herbs, ginger, curcumin, and even specialized supplement blends.
Vagus nerve stimulation is a popular social media trend for gut motility, Ms. Madsen said, but there isn't a lot of evidence of its efficacy. Still, she said it doesn’t hurt to try yoga, meditation, regular exercise, and deep breathing practices.
“I do think there’s some value in some of the techniques that are promoted because they also promote overall relaxation and stress reduction, which can have a big impact on gut health as well,” she said.