The Migrating Motor Complex (MMC) and SIBO

Have you ever wondered what causes the rumbling in your stomach between meals? Believe it or not, this rumbling is often a sign of healthy gut function! The migrating motor complex (MMC), often called the “housekeeper” of our gut, can get a little noisy as it cleans up our digestive tract in between meals.

In this article, we dive into:

  • How the MMC works
  • What conditions can disrupt the MMC
  • How dysfunction of the migrating motor complex is relevant to small intestinal bacterial overgrowth (SIBO)
  • What can be done to improve function

What is the Migrating Motor Complex?

The migrating motor complex is a series of muscle contractions that happen in our gut when we are not eating. The purpose of the MMC is to help move food particles and debris through the bowel. It also keeps the number of bacteria in the small bowel to a minimum.

These housekeeping waves start in the stomach and move through the small bowel. The waves cycle every 90-120 minutes in most people, though it can take longer.  Eating stops the waves from happening.

There are four phases of the migrating motor complex:

Phases of the Migrating Motor Complex: 1) Quiet, 2) Random Contractions, 3) Active, 4) Return to Quiet

In Phase 1 the gut is quiet and there are no contractions.

Phase 2 involves random contractions of the stomach and small intestine.

Phase 3 is the most active phase with the fastest and strongest contractions.

And in Phase 4 the contractions slow and become weaker.1

It is sometimes described as three phases (in this case phases 1 and 4 are combined).

How Our Body Regulates the Migrating Motor Complex

Hormones

There are many hormones involved with digestion. We won’t get into all the details here. But for those of you who want to geek out with me a little, here is a brief explanation of the two main hormones involved in the functioning of the MMC.  If you don’t care, feel free to move on to the next section!

Motilin is the main hormone involved in the MMC. It is produced in the small bowel and acts mostly on the stomach. It causes the stomach muscles to contract. Motilin levels are the highest in a fasted state, just before Phase 3 of the migrating motor complex. Levels decrease again with food intake.

Ghrelin is often referred to as the “hunger hormone”. It may also have an impact on Phase 3 of the MMC. Ghrelin is released from our body during fasting states and in response to low blood sugar.2

Phase 3 Contractions + Hormones = Rumbling Stomach

The increased contractions of the stomach and small intestine in the presence of the hunger hormone ghrelin and motilin may explain why we associate a rumbling or “growling” stomach with hunger.

Nerves

The nervous system also influences the migrating motor complex. The vagus nerve is the main nerve of the parasympathetic nervous system. And it is the main hub of the gut-brain axis.

You may hear the functions of this part of the nervous system referred to as “rest and digest” (versus the “fight or flight” functions of the sympathetic nervous system).

Researchers have discovered that the vagus nerve is most important for the contractions of the stomach.  Meanwhile, the enteric nervous system (the nerve cells in the wall of the intestines), plays a bigger role in the MMC of the small bowel1.

Disruptions to either the vagus nerve or the enteric nervous system can result in migrating motor complex dysfunction.

Conditions That May Cause Migrating Motor Complex Dysfunction

Below are a handful of conditions that can affect the migrating motor complex. These conditions may also increase the risk of small intestinal bacterial overgrowth (SIBO). Keep reading for more on how disruption to the MMC contributes to SIBO.

Vagotomy

A vagotomy is the surgical removal of part of the vagus nerve. This procedure was used in the past to help treat stomach ulcers. However, with improvements in other treatments, it is less common now. A vagotomy can affect the contractions of the stomach but has little effect on the small bowel.

Gastroparesis

Gastroparesis is a condition in which the stomach does not empty properly. It is sometimes referred to as delayed gastric (stomach) emptying. Gastroparesis can be the result of a damaged vagus nerve.

In gastroparesis, the stomach is slow to empty. This can be the result of a damaged vagus nerve and migrating motor complex dysfunction.

There are many causes of gastroparesis. Diabetes is a common cause. Nerve damage can occur when someone has persistent high blood sugar. The vagus nerve is one of the nerves that may be affected.

Scleroderma

Scleroderma is an autoimmune disorder that can affect the skin, connective tissue, and internal organs. It often affects gut motility.

Pseudo-obstructions may occur in severe cases of scleroderma. This is where there appears to be a blockage in the bowel although there is none. It causes enlargement of the bowel and is the result of lack of muscle contractions.

Eating Disorders

Gut symptoms are common in those with eating disorders. In some cases, the gut symptoms are what lead to the eating disorder. But in other cases, the eating disorder leads to disruptions in gut motility.

Eating disorders can affect the migrating motor complex

Anorexia nervosa has been associated with delayed gastric emptying and possibly alterations to the migrating motor complex. Treatment of the eating disorder and malnutrition can lead to restoration of gut function.3

Irritable Bowel Syndrome and the Migrating Motor Complex

Patients with IBS with diarrhea (IBS-D), may have more frequent MMC waves. While those with IBS with constipation (IBS-C) may have less frequent waves. Interestingly, these differences have only been found to occur while awake.4

There is some debate whether IBS causes changes to gut motility or if IBS results from these changes. A growing theory is that infections such as food poisoning or SIBO are behind the changes to gut motility that lead to IBS in many people. This type of IBS is often called post-infectious IBS and more commonly results in IBS-D.5

Increased Risk for SIBO

Understanding the “housekeeper” role of the migrating motor complex makes it easier to understand why dysfunction of the migrating motor complex might lead to small intestinal bacterial overgrowth (SIBO). 

When the gut is not moving as it is supposed to, food particles that should be cleared out by the MMC remain in the small bowel. Food that is not completely broken down by our digestive tract acts as fuel for gut bacteria.

The large intestine is where most of our gut bacteria live… or are supposed to live… When the gut is not moving at regular intervals, it can be easier for these gut bacteria to travel up from the colon and into the small intestine where they don’t belong.

With migrating motor complex dysfunction, bacteria that normally reside in the colon can make their way up to the small intestines to feed on debris.

These are not bad bacteria. In fact, most of these bacteria are good bacteria that are beneficial for our health… when they are present in the large intestine that is. In the case of SIBO they are doing their job in the wrong part of the gut, which is problematic.

In SIBO, when migrating motor complex is compromised, there is an increase in bacterial fermentation in the small intestine (fermentation = gas). This causes the symptoms of SIBO such as abdominal pain, bloating, and diarrhea.

SIBO is typically treated with antibiotics, but recurrence is common. However, getting to the root cause of SIBO can help prevent a recurrence.

For example, if SIBO is caused by gastroparesis, medications and diet changes can help get the stomach moving again. If SIBO is caused by IBS-C, the goal after treating SIBO is to achieve more regular bowel movements.

The Effect of SIBO on the Migrating Motor Complex

As discussed above, migrating motor complex dysfunction can increase the risk for SIBO. Unfortunately, if you get SIBO this can cause further disruptions to the MMC.

Migrating motor complex dysfunction can increase risk of SIBO. SIBO worsens gut motility.

This may seem counterintuitive if you have diarrhea as a symptom of SIBO.

The diarrhea that is experienced a result of SIBO is likely related to the byproducts that the bacteria produce. These are usually osmotic, meaning that they draw water into the bowel. This can lead to diarrhea.

Additionally, in more severe cases of SIBO there may be damage to the intestinal cells, a decrease in lactose tolerance, and changes in fat digestion that may lead to diarrhea.6

Natural Support of the Migrating Motor Complex

There are some diet and lifestyle strategies commonly recommended by clinicians to keep the migrating motor complex is functioning as well as it can.

While commonly used, these approaches are not well studied in the context of SIBO.  And not everyone is a good candidate to try these strategies. Please discuss with your healthcare provider before implementing these changes.

Meal Timing and the Migrating Motor Complex

Are you a perpetual snacker? Or a “three square meals” kind of person? Many clinicians propose that the “three squares” pattern is more helpful to stimulate the migrating motor complex.

Although the MMC generally cycles approximately every 90-120 minutes, there are times that the cycle can last nearly 4 hours. Therefore, a rule of thumb for meal spacing is 3-4 hours between meals or snacks.

Spacing Meals and Snacks 3-4 Hours Apart May Increase Cleaning Waves of the MMC

Remember that eating stops the migrating motor complex.

This might mean you need to eat larger meals when you do eat. It might also mean eating foods higher in fat, protein and / or fiber to help keep you full longer.

Therefore, if you do not tolerate large meals, this approach might not be a good fit. This is often the case for people who have delayed stomach emptying and in some people with IBS. A registered dietitian may be able to help you find a meal pattern that suits your needs.

Theoretically, the meal spacing strategy could be helpful in those who can tolerate it.  However, after a search through the literature and existing guidelines for SIBO, I came up empty handed on any studies that support this practice. Perhaps it will be an area for future research.

Between Meal Beverages

Along with meal spacing, timing of beverages can be important too.

Many people sip on coffee drinks with milk and sugar, tea with honey, energy drinks, soda, or juice throughout the day. Beverages are often a forgotten source of calories. And like any food you eat, a caloric beverage will stop the migrating motor complex.

So, what beverages won’t interfere with the migrating motor complex?

Water, black coffee, and tea without any sweeteners or cream should do. However, note that coffee and caffeine are common triggers for IBS. Check out this article for more on Coffee and IBS.

Again, limiting caloric beverages between meals is just a loose guideline. If you have trouble making it throughout the day without your beverage of choice, consider trying at least one stretch of 3-4 hours during the day without caloric beverages or food.

Intermittent Fasting and the Migrating Motor Complex

Some may consider meal spacing of 3-4 hours to be a type of intermittent fasting.  But most consider intermittent fasting as a longer period without eating, usually 10 hours or more.

Whatever your definition, intermittent fasting is another area of debate when it comes to SIBO.

Theoretically, this sounds great to give your body more time without food to complete more cycles of the MMC. However, there is no data to support that it works to prevent SIBO.

There are several approaches to intermittent fasting. These include extended overnight fasting, alternate day fasting, and fasting two days a week.

The most popular approach to intermittent fasting, which might also be the easiest and safest, is the extended overnight fast. You may also hear this approach referred to as time-restrictive eating.

This usually involves a period of 12 – 16 hours of fasting that spans overnight. It is followed by a shorter window for eating during the day.

The migrating motor complex has more time to work overnight. However, there is evidence that the MMC has a circadian rhythm. It has been observed that the strength the MMC is reduced at night.4

Still, by extending the fasting period overnight there will also be an increased period without food during waking hours when the migrating motor complex is more active.

Can intermittent fasting help migrating motor dysfunction?

Problems with this approach are that it may be difficult to get adequate nutrition in this shorter timeframe for eating. It may also make meal spacing during the eating period more difficult to achieve. 

Again, I came up empty-handed when searching for any evidence to support the use of intermittent fasting to help treat or prevent SIBO.

Intermittent fasting can be dangerous for some people. Discuss with your healthcare team if you are interested in trying this intervention.

Medical Treatment

Medical treatment for disruption to the migrating motor complex will depend on your diagnosis. Your treatment plan may include medications, diet, and lifestyle changes.

If you are on multiple medications, a review of these medications by a pharmacist can help determine if they are part of the problem. There are several medications with a side effect of slowing motility.

Prokinetics are medications that speed up gut motility. They are common in the treatment of gastroparesis or delayed gastric emptying. 

If SIBO itself is impairing your migrating motor complex, the most common treatment is antibiotics. Some clinicians also use herbs with antibiotic properties.

A low FODMAP or low fermentation diet may be used alongside antibiotic therapy. Diet changes help control the symptoms of SIBO. They do not treat the condition.

For more on a low FODMAP diet, see this article on The FODMAP Elimination Diet.

Summary

The migrating motor complex is the “housekeeper” of the gut, keeping your gut nice and tidy in between meals.

The Migrating Motor Complex (the housekeeper)

However, some people experience migrting motor dysfunction. These individuals may be at higher risk for SIBO.

Once you get SIBO it can be a vicious cycle, slowing down the MMC even more. To assure proper functioning, it is important to treat the SIBO (if present) and find any other causes to the disruption to the MMC.

Medical treatment may be needed to treat the underlying cause of the disruption to the MMC.

Increased meal spacing and intermittent fasting are dietary approaches that a frequently used after SBIO treatment to prevent a recurrence. These strategies are meant to give the MMC more uninterrupted time to function.

However, these strategies are not right for everyone. Discuss the pros and cons with your healthcare team.

References

1.         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;9(5):271-285. doi:10.1038/nrgastro.2012.57

2.         Alamri BN, Shin K, Chappe V, Anini Y. The role of ghrelin in the regulation of glucose homeostasis. Horm Mol Biol Clin Investig. 2016;26(1):3-11. doi:10.1515/hmbci-2016-0018

3.         Schalla MA, Stengel A. Gastrointestinal alterations in anorexia nervosa — A systematic review. Eur Eat Disord Rev. 2019;27(5):447-461. doi:10.1002/erv.2679

4.         Gorard DA, Vesselinova-Jenkins CK, Libby GW, Farthing MJG. Migrating motor complex and sleep in health and irritable bowel syndrome. Dig Dis Sci. 1995;40(11):2383-2389. doi:10.1007/BF02063242

5.         Pimentel M, Morales W, Rezaie A, et al. Development and validation of a biomarker for diarrhea-predominant irritable bowel syndrome in human subjects. PLoS One. 2015;10(5):1-12. doi:10.1371/journal.pone.0126438

6.         Sachdev AH, Pimentel M. Gastrointestinal bacterial overgrowth : pathogenesis and clinical significance. Published online 2013:223-231. doi:10.1177/2040622313496126

Remember: this post is for informational purposes only and may not be the best fit for you and your personal situation. It shall not be construed as medical advice. The information and education provided here is not intended or implied to supplement or replace professional medical treatment, advice, and/or diagnosis. Always check with your own physician or medical professional before trying or implementing any information read here.

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