What Is Small Intestinal Bacterial Overgrowth?
Small Intestinal Bacterial Overgrowth (SIBO), is a form of gut dysbiosis resulting from excessive bacteria growth in the small intestine. [1] Whilst we do require some bacteria in our small intestine, the concentration of the bacteria in the small intestine rarely exceeds 1000 organisms/ml in healthy individuals. The small intestine is not a sterile environment, but bacteria levels are significantly lower in number when compared to the large intestine. [2]
A normal and healthy gut will work to keep the volume of bacteria regulated, low, and optimal. Ordinarily, gastric acid secretions and intestinal motility limit the growth of bacteria in the small intestine. Pancreatic and biliary secretions also have bacteriostatic properties, which means they help to stop bacteria from reproducing and proliferating. [2] [3]
Interruptions or failures of these biological functions can lead to the intestinal flora growing to higher volumes than normal, leading to SIBO developing. If the bacteria strains begin to colonise the small intestine in significant numbers, this is the start of SIBO. Sometimes, SIBO can simply be the overgrowth of the wrong species of bacteria. Some bacteria strains are beneficial to our health and aid digestion, but others can cause pronounced health issues if allowed to gain dominion. As with many things, the right balance is the key.
The symptoms and effects of SIBO rather depend on the strains of bacteria involved and how numerous they are. This aspect of SIBO makes it notoriously difficult to correctly diagnose with current diagnostic methods and present understanding of the intestinal biome.
What are some of the symptoms of SIBO? The symptoms and effects of SIBO rather depend on the strains of bacteria involved and how numerous they are. This aspect of SIBO makes it notoriously difficult to correctly diagnose with current diagnostic methods and present understanding of the intestinal biome. Despite this variation in how SIBO manifests, there are indeed some common symptoms usually present across cases. SIBO usually leads to a wide spectrum of symptoms with the most common being;
● Brain Fog.
● Depression.
● Bloating and abdominal pains.
● Muscle Aches.
● Fatigue.
● Malabsorption and nutritional deficiencies. [3]
● Diarrhoea or Constipation (depending on bacteria strains present).
This wide range of symptoms makes SIBO particularly hard to diagnose and treat, as it may not be immediately obvious that the symptoms are linked. These symptoms however, can prove to be very debilitating and life changing, so it is wise and worthwhile for us to takes steps to avoid letting SIBO develop.
What Causes SIBO?
There are certain behaviours and lifestyle actions that can provide the conditions for SIBO to arise. Clearly, some individuals will have more of a predisposition to developing SIBO than others, such as those with slower than normal gastric transit, reduced gut motility, or immune system dysfunction. A 2010 Study listed several potential risk factors that increase the liklihood of an individual developing SIBO. These include;
● Disorders of innate protective antibacterial mechanisms such as achlorhydria, pancreatic exocrine insufficiency, and immunodeficiency syndromes.
● Anatomical Abnormalities such as small intestinal obstructions, diverticula, fistulae, surgical blind loop, and previous ileo-caecal resections.
● Motility disorders such as scleroderma, post-radiation enteropathy, small intestinal pseudo-obstruction, and autonomic neuropathy in diabetes mellitus.
Bures J, Cyrany J, Kohoutova D, Förstl M, Rejchrt S, Kvetina J, Vorisek V, Kopacova M. – Small Intestinal Bacterial Overgrowth Syndrome [3]
These medical conditions certainly are among the main risk factors for SIBO, yet even amongst otherwise healthy populations, SIBO cases have been on a dramatic increase in the Western world in the past couple of decades. Statistics suggest around 11% of the global population experience IBS, and some estimates suggesting that 80% of IBS cases are fundamentally cases of SIBO in their nature. [4] [5]
Regardless of the exact number, it seems that SIBO is a condition that is growing in frequency each year, and already affects millions of people. What could be the cause of such a meteoric rise? SIBO can come in many forms, and so unsurprisingly, there are many different potential causes and risk factors that can lead to it’s development.
By understanding the factors that contribute to SIBO developing, we can try to prevent it getting a foothold. With that in mind, let’s now take a look at three of the most common factors that contribute to SIBO, and give an overview of how and why these behaviours can put an individual at risk of disrupting the intestinal flora.
SIBO Risk Factors
1. Taking Certain Medications
One of the most common factors that can set the stage for SIBO is when an individual is taking medications that slow down the speed of intestinal transit or directly alter the microbiome. When we introduce medications that disrupt our digestion (often through the brute force triggering of certain receptors in our nervous system) we inadvertantly change the mechanics and rhythm of a complex system.
Which medications can cause SIBO? There are gastrointestinal side effects from many medications, but a few have been demonstrated in studies to contribute to SIBO development. Here are three of the main classes of drugs that can cause a SIBO infection.
Proton pump inhibitors (PPIs) have been shown in research to be a causal factor in SIBO development. Proton Pump Inhibitors are drugs commonly prescribed for individuals experiencing issues with acid reflux, as they are effective at reducing gastric acid secretion. As these secretions are vital in preventing bacterial buildup, it is perhaps no surprise that several meta-analyses and systematic reviews have reported that patients treated with PPIs have a higher frequency of SIBO. [6]
Often, these medications are prescribed alongside anti-inflammatory medications (NSAIDs) to mitigate the well known gastrointestinal impact that NSAIDs have. This practice is very common, but may be an over simplified and potentially harmful interpretation of the intended use of Proton Pump Inhibitors. Recent evidence indicates that the gastrointestinal risks associated with NSAIDs can actually be potentiated when they are combined with PPIs, a total inversion of the reason they are prescribed in the first place! [7]
Opioid And Opiate Painkillers
Opioid And Opiate painkillers are the most commonly prescribed medications for treating pain, and many people experiencing digestive issues or abdominal pain may find themselves taking such medication for some much needed relief. Codeine, Tramadol, and Oxycodone are some of the most commonly taken examples of such medications.
Constipation is a well known side effect from these drugs, so it is perhaps to be expected that research has shown that opioids and opiates cause a slowed intestinal transit time for food. [8] This is a concern, as there is a significant evidence that slower small bowel transit times predispose individuals to the development of SIBO. [9]
Opiates also inhibit many intestinal secretions via their action on the enteric nervous system and in the central nervous system. [10] This side effect of opioid painkillers is particularly unhelpful for those who already have SIBO. As we discussed in the opening section, many of these secretions play an important role in controlling the levels of bacteria reproduction. Slower intestinaltransit times and decreased intestinal secretions can cause digestive issues, and a disruption of our natural microbiome. Research conducted in 2019 found that ‘a persistent decrease in gastrointestinal motility induced by opioids is a primary cause of gut microbial dysbiosis’. [11]
Counterintuitively, opioids are often prescribed to patients that present IBS symptom profiles to manage abdominal pain and cramping. Though well intentioned, such practices could ultimately be making the situation for the patient worse, leading to changes in the intestinal microbiota and potentially triggering SIBO development. Alternative pain management strategies could provide a solution to this, and safe alternatives are worth considering.
If opioids are to be used, then it is worth trying to ensure that bowel transit times remain normal, and avoiding constipation. [11] This could be done via the use of gentle laxatives such as magnesium gluconate. Whilst this is not a full solution to the issue, it is something to keep in mind if alternatives to opioids are not suitable or available. It should be noted however, that even the use of laxatives does not fully avoid the risk of SIBO development. This is because even when bowel movements are regular, opioids still reduce gastric motility in a multitude of other ways, causing food matter to remain in the gut lumen for longer durations. [12]
Broad Spectrum Antibiotics
Although it may initially seem like antibiotics would be helpful in preventing SIBO, they too can cause the onset of SIBO. This is because of the drastic effect that broad spectrum antibiotics have on the intestinal microbiota. Certain antibiotics can kill off beneficial bacteria strains as well as pathogenic ones, and in this unbalanced state, pathogenic bacteria strains can get a foothold. [13] When individuals are prescribed antibiotics for an infection, both the doctor and the patient may simply focus on it’s effects for the ailment in question. Often however, there can be collateral damage in the gastrointestinal tract.
A 2018 study found that antibiotics disrupted the microbiota significantly. “Alterations in microbial communities lead to changes in functional structures based on the metabolites produced in the gut, and these environmental changes result in various bacterial infections and chronic enteric inflammatory diseases.” [14]
Common features of post-antibiotic dysbiosis include a loss of taxonomic and functional diversity combined with reduced colonization resistance against invading pathogens, which harbors the danger of antimicrobial resistance. [15] These disruptions to the microbiota can lead to cases of SIBO.
To attempt to reduce the impact of antibiotics on the intestinal microbiome, individuals taking these types of medications are often recomended to increase intake of probiotics. This could be in the form of fermented foods such as yoghurt with active cultures, kimchi, kefir, or sourkraut. Probiotic supplements can also provide a source of beneficial bacteria cultures to replenish depleted numbers.
2. Eating Food At The Wrong Times
Our biological systems are synchronised with our body clocks, and many of our bodies processes play out over a 24 hour cycle. These are called our circadian rhythms, and our digestive system also runs in accordance with daily cycles. Secretions of enzymes, bowel movements, gastric acid secretions, and more are all linked to our body clock. This means that there are times of day when our body is prepared for food and times when it is not. By timing our meals in the right way, we can help support our digestive system to operate in the most efficient way possible.
Eating just before going to bed is not advised. This is because our digestion slows during sleep. [16]
As a result, this leads to a slowed gastric transit and result in food matter spending longer than usual in the small intestine. This would provide bacteria with a large amount of food and time to consume it, thus allowing them to thrive and proliferate their numbers. This effect is amplified as our digestive system functions best when we are upright. Laying flat during the digestion process will again lead to slower and suboptimal digestion of foods.
It is also important to keep the Migrating Motor Complex (MMC) in mind when choosing meal and snack times. The MMC is a recurring motility pattern that occurs in the stomach and small intestine that helps move food matter through the digestive system. [17]
The MMC can be thought of as a natural and inbuilt maintenance mechanism for our gastrointestinal tract. If you have ever worked in an office that has a cleaning staff arrive after hours, this is a good metaphor for the Migrating Motor Complex. But like those cleaning teams, the mechanism can only get to work once everything is quiet, and eating foods stops the process. The MMC is interrupted by eating, and usually begins to get to work around three hours after a meal. Indeed, often three hours after meals, it is common for people to be able to physically feel this cycle as their stomach begins to gurgle and rumble.
This cycle is regulated by electrical activity in the nerves, and the vagus nerve is a primary driver in this cycle operating. The nerve stimulation triggers the downward movement of food matter, and thus provides a natural flushing mechanism against food waste, parasites, undigestible matter and of course, bacteria. The physical sensations of the MMC in action can feel very similar to a mild hunger, and so this can sometimes prompt people to grab a snack. Unfortunately, this interrupts and stops the cycle, resetting the timer for another three hours.
The MMC has huge implications for SIBO cases. Individuals who suffer disruption or damage to this system are far more likely to develop SIBO. A study in 2012 stated that “The physiological role of the MMC is incompletely understood, but its absence has been associated with gastroparesis, intestinal pseudo-obstruction and small intestinal bacterial overgrowth.” [18]
A good solution to this issue for the majority of people is to go through an extended overnight fast. This is much easier than it sounds, and simply relies on us not eating anything after dinner, leaving plenty of time for the MMC to do it’s work until breakfast. In this way, we can provide periods of around 14 hours for the MMC to get to work in flushing out what it needs to.
3. Poor Diet
One of the most common and avoidable risk factors of SIBO development is a diet consisting of excessive sugar and carbohydrate intake. In the modern world, many of our meals are based primarily on carbohydrates, and it is at times too easy to eat sugary snacks. Indeed, refined grains, starchy vegetables, and added sugars account for 42 percent of the average American’s daily calories. [19]
Chocolates, cakes, biscuits, pastries, doughnuts, and other sweet treats are easily obtainable and their tempting nature has led to them becoming commonplace in the modern diet. This is especially the case for those who are overworked and tired, as picking up a quick sugar-boosting food is a quick and easy way to fight back hunger.
As delicious as these types of foods can be, unfortunately, there are certain intestinal bacteria strains that love to eat these foods. As we eat, our intestinal flora also eat, and what we eat, they also eat. Eliminating junk food from the diet can help in promoting a healthy microbiome, and serve to reduce the likelihood of SIBO developing.
Alcohol is also something that should be avoided when considering SIBO, as alcohol has also been shown to disrupt the microbiome. [20] [21] ‘Clinical and preclinical data suggest that alcohol-related disorders are associated with quantitative and qualitative dysbiotic changes in the intestinal microbiota and may be associated with increased gastrointestinal tract inflammation and intestinal hyperpermeability’. These changes in the gut can lead to endotoxemia, systemic inflammation, and tissue damage.
Avoiding alcohol consumption can help to promote healthy intestinal microbiota and reduce the adverse effects it has on the digestive system.
Conclusion
Each of these risk factors presents a potential piece of the jigsaw for SIBO developing. When all three factors are combined, it can set the stage for the overgrowth of many pathogenic strains of bacteria in the gastrointestinal tract.
Following these steps is not a guarantee that SIBO will not develop, but by avoiding these common causes, you will greatly reduce your chances of allowing it to get started. For those that have recovered from SIBO in the past, these steps become even more imperative.
By avoiding or limit the use of prescription medications that are known to disrupt or damage the intestinal microbiota, eat the right foods at the right times, you will make it much more likely that you will develop a healthy intestinal microbiome. Alcohol is very disruptive to the intestines and microbiome, and is best avoided entirely.
